U.S. patent application number 11/887440 was filed with the patent office on 2009-05-28 for electroosmosis pump and liquid feeding device.
This patent application is currently assigned to Nano Fusion Technologies Inc.. Invention is credited to Masana Nishikawa, Ichiro Yanagisawa.
Application Number | 20090136362 11/887440 |
Document ID | / |
Family ID | 37073439 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090136362 |
Kind Code |
A1 |
Yanagisawa; Ichiro ; et
al. |
May 28, 2009 |
Electroosmosis Pump and Liquid Feeding Device
Abstract
In an electroosmosis pump, a bubble separation member is
provided at an exit side chamber so as to be separated from an exit
side electrode, a gas vent member is provided at that side section
of a pump container which is near the exit side electrode, and a
gas vent member is provided at that side section of the pump
container which is near an entrance side electrode. A self-filling
mechanism is placed in an entrance side chamber, and the
self-filling mechanism is composed of a liquid drawing member in
contact with an electroosmosis material via the entrance side
electrode, and of an air vent path formed between a member
surrounding a side section of the liquid drawing member and the
inner wall of the pump container.
Inventors: |
Yanagisawa; Ichiro; (
Saitama-ken, JP) ; Nishikawa; Masana; (Tokyo,
JP) |
Correspondence
Address: |
STEPTOE & JOHNSON LLP
1330 CONNECTICUT AVENUE, N.W.
WASHINGTON
DC
20036
US
|
Assignee: |
Nano Fusion Technologies
Inc.
Tokyo
JP
|
Family ID: |
37073439 |
Appl. No.: |
11/887440 |
Filed: |
March 30, 2006 |
PCT Filed: |
March 30, 2006 |
PCT NO: |
PCT/JP2006/306757 |
371 Date: |
September 28, 2007 |
Current U.S.
Class: |
417/48 ;
417/379 |
Current CPC
Class: |
F04B 17/00 20130101;
B01L 3/5027 20130101 |
Class at
Publication: |
417/48 ;
417/379 |
International
Class: |
F04F 99/00 20090101
F04F099/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2005 |
JP |
2005 099555 |
Claims
1. An electroosmotic pump including a first electrode and a second
electrode disposed upstream and downstream, respectively, from an
electroosmotic member disposed in a fluid passage, wherein, when a
voltage is applied to said first electrode and said second
electrode, a drive liquid is caused to flow in said fluid passage
through said electroosmotic member, characterized in that a
downstream liquid passing member, for preventing gas produced in
the vicinity of said second electrode when said voltage is applied
from passing downstream, and for passing the drive liquid
therethrough, is disposed downstream from said second electrode on
a downstream side of said fluid passage.
2. An electroosmotic pump according to claim 1, characterized in
that a downstream gas vent, for discharging said gas out of said
fluid passage to outside, is disposed between said electroosmotic
member and said downstream liquid passing member.
3. An electroosmotic pump according to claim 1, characterized in
that an upstream liquid passing member, for preventing foreign
matter from flowing into said electroosmotic member and passing
said drive liquid therethrough when said voltage is applied, is
disposed upstream from said electroosmotic member on an upstream
side of said fluid passage.
4. An electroosmotic pump according to claim 3, characterized in
that an upstream gas vent, for discharging gas produced in the
vicinity of said first electrode, to outside, when said voltage is
applied, is disposed between said electroosmotic member and said
upstream liquid passing member.
5. An electroosmotic pump according to claim 1, characterized in
that an upstream liquid self-priming mechanisms, for self-priming
said drive liquid, is disposed on an upstream side of said fluid
passage in contact with one of said electroosmotic member and said
first electrode.
6. An electroosmotic pump according to claim 1, characterized in
that a downstream liquid self-priming mechanism, for self-priming
said drive liquid, is disposed on a downstream side of said fluid
passage in contact with one of said electroosmotic member and said
second electrode.
7. An electroosmotic pump including a first electrode and a second
electrode disposed upstream and downstream, respectively, from an
electroosmotic member disposed in a fluid passage, wherein, when a
voltage is applied to said first electrode and said second
electrode, a drive liquid is caused to flow in said fluid passage
through said electroosmotic member, characterized in that an
upstream liquid self-priming mechanism, for self-priming said drive
liquid, is disposed on an upstream side of said fluid passage in
contact with one of said electroosmotic member and said first
electrode.
8. An electroosmotic pump according to claim 7, characterized in
that an upstream liquid passing member, for preventing foreign
matter from flowing into said electroosmotic member and passing
said drive liquid therethrough when said voltage is applied, is
disposed upstream from said electroosmotic member on an upstream
side of said fluid passage.
9. An electroosmotic pump according to claim 8, characterized in
that an upstream gas vent, for discharging gas produced in the
vicinity of said first electrode to outside when said voltage is
applied, is disposed between said electroosmotic member and said
upstream liquid passing member.
10. An electroosmotic pump according to claim 7, characterized in
that a downstream liquid self-priming mechanism, for self-priming
said drive liquid, is disposed on a downstream side of said fluid
passage in contact with one of said electroosmotic member and said
second electrodes.
11. An electroosmotic pump according to claim 7, characterized in
that a downstream liquid passing member, for preventing said gas
from passing downstream and passing said drive liquid therethrough,
is disposed downstream from said second electrode on a downstream
side of said fluid passage.
12. An electroosmotic pump according to claim 11, characterized in
that a downstream gas vent, for discharging gas produced in the
vicinity of said second electrode to outside when said voltage is
applied, is disposed between said electroosmotic member and said
downstream liquid passing member.
13. An electroosmotic pump according to claim 12, characterized in
that said liquid passing member is made of a hydrophilic material;
a gas pressure required for gas to pass through said liquid passing
member is 1 [kPa] or higher; and said liquid passing member has a
thickness of 3 [mm] or less along a direction of said fluid
passage.
14. An electroosmotic pump according to claim 12, characterized in
that said gas vent is made of a hydrophobic material disposed on a
side wall of said fluid passage; a pressure under which said drive
liquid passes over said gas vent is larger than a maximum pressure
of said drive liquid when said electroosmotic pump is in operation;
and said gas vent has a thickness of 3 [mm] or less along the
direction in which said gas passes.
15. An electroosmotic pump according to claim 7, characterized in
that said liquid self-priming mechanism comprises a self-priming
member disposed in the vicinity of said electroosmotic member along
said fluid passage, and an air vent disposed alongside said
self-priming member and having an impregnation pressure that is
different from the impregnation pressure of said self-priming
member; and said self-priming member is self-primed with said drive
liquid and supplies said drive liquid to said electroosmotic
member, and said air vent discharges air remaining upstream from
said electroosmotic member, to outside, based on an impregnation
pressure difference between said self-priming member and said air
vent.
16. An electroosmotic pump according to claim 15, characterized in
that said self-priming member is made of a hydrophilic material and
said air vent is made of a hydrophobic material.
17. An electroosmotic pump according to claim 11, characterized in
that said electroosmotic member or said first electrode and said
upstream liquid passing member are spaced from each other by an
interval of 3 [mm] or less along the direction of said fluid
passage, and/or said electroosmotic member or said second electrode
and said downstream liquid passing member are spaced from each
other by an interval of 3 [mm] or less along the direction of said
fluid passage.
18. An electroosmotic pump according to claim 7, characterized in
that a drive liquid absorbing member made of a hydrophilic
material, which closely contacts with said upstream liquid
self-priming mechanism and said electroosmotic member or said first
electrode, is disposed between said upstream liquid self-priming
mechanism and said electroosmotic member or said first electrode,
and/or a drive liquid absorbing member made of a hydrophilic
material, which closely contacts with said downstream liquid
self-priming mechanism and said electroosmotic member or said
second electrode, is disposed between said downstream liquid
self-priming mechanism and said electroosmotic member or said
second electrode.
19. An electroosmotic pump according to claim 7, characterized in
that said fluid passage is defined in a pump casing accommodating
therein said electroosmotic member, said first electrode, and said
second electrode; and said fluid passage has an upstream inlet and
a downstream outlet defined in one surface of said pump casing.
20. A liquid feeding device comprising: an electroosmotic pump
according to claim 7; and a liquid container filled with a liquid,
wherein said liquid in said liquid container is supplied to outside
by said electroosmotic pump.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electroosmotic pump
(electroosmosis pump) suitable for use in controlling movement of a
liquid in a microfluid chip for use in biotechnology, analytical
chemistry, or the like, or for controlling movement of a fluid in a
mobile electronic device, as well as to a liquid feeding device
incorporating such an electroosmotic pump therein.
BACKGROUND ART
[0002] Electroosmotic pumps are pumps for transporting a fluid
based on an electroosmotic phenomenon, and are used as fluid moving
means in capillaries and microfluid chips, for example.
[0003] Based on the fact that an electroosmotic phenomenon
manifests itself within a very narrow fluid passage having a width
of several hundreds [.mu.m] or less, the capillary diameter is set
to several hundreds [.mu.m] or less, or the width of the fluid
passage within a microfluid chip is set to several tens [.mu.m],
for example, and two electrodes (positive and negative electrodes)
are disposed in the capillary or the fluid passage, thereby turning
the capillary or the fluid passage into a pump.
[0004] FIG. 38 shows an electroosmotic pump 200 including
reservoirs 202, 204, each containing an electrolytic solution,
which are connected to each other by a capillary 206 filled with
the electrolytic solution. When a DC power supply 208 applies a DC
voltage between electrodes 210, 212 disposed respectively in the
reservoirs 202, 204, the electrolytic solution is transported from
the reservoir 202 to the reservoir 204 through the capillary
206.
[0005] The electroosmotic pump 200 is advantageous in that (1) the
electroosmostic pump can flow electrolytic solution without
pulsations, (2) the electroosmotic pump 200 is easy to use since
the electrolytic solution can be displaced simply by inserting the
electrodes 210, 212 into the reservoirs 202, 204 and applying a DC
voltage therebetween, and (3) the electroosmotic pump 200 has no
mechanically movable parts and is simple in structure. Therefore,
use of the electroosmotic pump in macroscopic applications of about
several [mm], which are constructed of only narrow fluid passages,
has been considered.
[0006] FIG. 39 shows an electroosmotic pump 214, which is a smaller
version of the electroosmotic pump 200 (see FIG. 38). The
electroosmotic pump 214 comprises an electroosmotic member 220 of
an electroosmotic material (hereinafter referred to as an EO
material) disposed in a fluid passage 218 defined in a pump case
216, and electrodes 222, 224 disposed on upstream and downstream
sides, respectively, of the electroosmotic member 220 and having a
plurality of pores defined therein along the direction of the fluid
passage. The electrodes are not limited to the illustrated
structure, but may also be in the form of wires.
[0007] If porous material or a filled structure of minute particles
or fibers, or the like, which exhibit electroosmosis, are used as
the EO material, then it is possible to transport an electrolytic
solution at a flow rate within a range of from [.mu.L/min] to
[mL/min] or higher without the need for a capillary 206 (see FIG.
38) and/or a fluid passage within the microfluid chip (see
non-patent Documents 1 through 3).
[0008] Concerning the DC voltage applied to the electrodes 210,
212, 222, 224 from the DC power supply 208, while the
electroosmotic pump 200 (see FIG. 38) needs to have a DC voltage of
several tens [kV], the electroosmotic pump 214 allows the
electrolytic solution to be moved under a DC voltage of only about
several [V].
[0009] If the electrolytic solution can be transported under a low
voltage at a large flow rate under a desired drive pressure, then
electroosmotic pumps are free of the limitations imposed by using
the small-diameter capillary 206 and the fluid passage in the
microfluid chip, and hence the electroosmotic pump 214 can be used
in an increased range of applications.
[0010] FIG. 40 shows an electroosmotic pump 230 devised by the
present applicant. The electroosmotic pump 230 includes a reservoir
232 disposed in an upper portion thereof and containing an
electrolytic solution. The electroosmotic pump 230 has a lower
portion connected to a fluid passage 236 of a microfluid chip 234.
When a DC voltage in the range from several [V] to 30 [V] is
applied between electrodes 222, 224, the electrolytic solution is
supplied from the reservoir 232 to the fluid passage 236, at a
maximum rate of about several tens [.mu.L/min] and under a maximum
pressure of 100 [kPa] or higher.
[0011] Non-patent Document 1: U.S. Published Application No.
2003/0068229
[0012] Non-patent Document 2: U.S. Pat. No. 3,923,426
[0013] Non-patent Document 3: U.S. Published Application No.
2004/0234378
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0014] Since electroosmosis is an electrochemical phenomenon, when
the DC voltage is applied between the electrodes 222, 224 by the DC
power supply 208, gas is produced in the vicinity of the electrodes
222, 224. Any gas which has not been dissolved into the
electrolytic solution floats as bubbles in the electrolytic
solution, wherein such floating bubbles tend to cause the flow
within the fluid passage 236 to become unstable, thus causing an
operational failure of the electroosmotic pump 214, and greatly
affecting various measurements, such as chemical reactions and
chemical analyses that take place downstream from the fluid passage
236.
[0015] More specifically, the electroosmotic pump 214 is generally
a system wherein ionic electrical conduction in the electrolytic
solution and electronic conduction at the electrodes 222, 224 exist
together. At the electrodes 222, 224, a gas is produced upon charge
exchange therebetween.
[0016] For example, in FIG. 39, if the drive liquid is an aqueous
solution, wherein the zeta potential of the electroosmotic member
220 has a negative potential, the upstream electrode 222 is a
positive electrode, and the downstream electrode 224 is a negative
electrode, then when a DC voltage is applied between the electrodes
222, 224 by the DC power supply 208, an electrochemical reaction
brings about the following reaction in the vicinity of the
electrodes 222, 224:
2H.sub.2O.fwdarw.2H.sub.2+O.sub.2 (1)
[0017] As a result, hydrogen gas is produced at the electrode 224
(negative) and oxygen gas is produced at the electrode 222
(positive). If the amount of hydrogen produced near the electrode
224 is in excess of the solubility of the electrolytic solution,
bubbles are generated by the hydrogen gas and flow into the system
downstream from the electroosmotic pump 214.
[0018] When the electroosmotic pump 214 is used to control
displacement of a minute fluid in a microfluid chip that is
connected downstream from the electroosmotic pump 214, bubbles
flowing into the channel of the microfluid chip make it difficult
to perform accurate positional control over the minute fluid.
[0019] Bubbles also tend to significantly affect a sensor and an
actuator in the system. For example, when a thermal flow rate
sensor is used to control the flow rate of a minute fluid, bubbles
make it difficult for the thermal flow rate sensor to measure the
flow rate accurately, with the result that a feedback control
cannot be performed with the thermal flow rate sensor.
[0020] Through holes defined in the electroosmotic member 220 have
a diameter on the order of [.mu.m] or less. Consequently, oxygen
gas produced in the vicinity of the electrode 222 does not pass
through the electroosmotic member 220, but covers the surface of
the electrode 222 or the electroosmotic member 220. As a result,
the area of contact between the electrode 222 or the electroosmotic
member 220 and the aqueous solution is reduced, thereby distorting
the electric field distribution within the electroosmotic member
220, and obstructing the flow of the electrolytic solution through
the electroosmotic member 220. Therefore, the performance of the
pump is lowered due to flow rate reduction, flow shutdown, or the
like.
[0021] If the electric field intensity between the electrodes 222,
224 is increased for the purpose of increasing the pump flow rate,
then the increased electric field intensity causes more bubbles to
be generated.
[0022] The electroosmotic pump 214 often employs an electrolytic
solution (buffer solution or the like) having a high electric
conductivity as a drive liquid for the purpose of stabilizing
electroosmosis. The electric current that flows between the
electrodes 222, 224 increases by necessity when the DC voltage is
applied to the electrodes 222, 224, thus promoting the generation
of gas.
[0023] When the electroosmotic pump 214 is applied to biology,
medical treatments, and microelectronics-related devices,
therefore, the above gas generation problem needs to be solved in
order to stabilize pump performance and increase pump
efficiency.
[0024] Some countermeasures have heretofore been considered with
respect to the generation of gas. According to a first
countermeasure, the electrodes are made of an ion-conductive
material, wherein the ion-conductive material is electrically
connected to an electron conductor outside of the electroosmotic
pump 214, so that gas is generated outside of the electroosmotic
pump 214. Although the problem of gas generation within the
electroosmotic pump 214 can be avoided, the entire system tends to
be complex, since there is a need to convert ionic conduction into
electron conduction outside of the electroosmotic pumps 200, 214,
230.
[0025] According to the second countermeasure, the fluid passage of
the electroosmotic pump 214 is constructed as a closed-loop fluid
passage, wherein oxygen gas and hydrogen gas that are produced are
converted into water, by means of a recombiner employing a
catalyst. However, since the size of the electroosmotic pump 214 to
which the present invention relates is in a range of from several
[mm] to several [cm], so that the pump can be housed within a small
mobile device and installed on a microfluid chip, use of a
recombiner increases the size of the pump and makes the pump
complex in structure.
[0026] A tank or a cartridge is connected to the upstream side of
the electroosmotic pump 214 for supplying an electrolytic solution
to the electroosmotic member 220. If the electroosmotic pump 214 is
used as a general-purpose device over a wide range of applications,
then it is necessary to supply the electroosmotic member 220
reliably with the electrolytic solution as well as to reliably
discharge the electrolytic solution from the electroosmotic member
220 to devices downstream from the electroosmotic pump 214. The
electroosmotic member 220 is made of an impregnation material
having a so-called self-priming capability for absorbing the
electrolytic solution and discharging it downstream when the
electrolytic solution to be driven reaches the upstream surface of
the electroosmotic member 220.
[0027] With the electroosmotic pump 214, however, when drive liquid
flows from the upstream side, if the fluid passage 218 upstream
from the electroosmotic member 220 is narrow (several [mm] or
less), then the drive liquid finds it hard to expel gas in the
vicinity of the electrode 222 while fully filling the upstream
region of the electroosmotic member 220, and hence gas is confined
in the upstream region of the electroosmotic member 220.
Consequently, the drive liquid does not reach the surface of the
electrode 222 on the electroosmotic member 220, and the
electroosmotic pump 214 may fail to operate or have its pumping
capability lowered.
[0028] The present invention has been made in view of the above
problems. It is an object of the present invention to provide an
electroosmotic pump, which is capable of preventing a gas generated
near an electrode from flowing downstream.
[0029] Another object of the present invention is to provide an
electroosmotic pump, which is capable of reliably supplying the
electroosmotic member with a drive liquid.
[0030] Still another object of the present invention is to provide
an electroosmotic pump having a simple structure, which is capable
of supplying a liquid filling a liquid container to an external
device.
Means for Solving the Problems
[0031] An electroosmotic pump according to the present invention
includes a first electrode and a second electrode disposed upstream
and downstream, respectively, of an electroosmotic member disposed
in a fluid passage, wherein when a voltage is applied to the first
electrode and the second electrode, a drive liquid is caused to
flow in the fluid passage through the electroosmotic member,
characterized in that a downstream liquid passing member, for
preventing gas produced in the vicinity of the second electrode
when voltage is applied thereto from passing downstream while
permitting passage of the drive liquid therethrough, is disposed
downstream from the second electrode on a downstream side of the
fluid passage.
[0032] With the above arrangement, even when gas is produced near
the second electrode by application of the voltage, the downstream
liquid passing member disposed downstream from the electroosmotic
member allows the drive liquid to pass, while preventing gas from
passing therethrough. Accordingly, gas is prevented from being
introduced into any of various fluid devices, such as a microfluid
chip or the like, connected to the downstream side of the fluid
passage, and the electroosmotic pump can accurately control the
position of the liquid that passes through the fluid device, for
example.
[0033] A downstream gas vent for discharging gas outside of the
fluid passage should preferably be disposed between the
electroosmotic member and the downstream liquid passing member. In
this case, since gas produced in the vicinity of the second
electrode is discharged outside through the downstream gas vent,
when the electroosmotic pump is operated over a long period of
time, the performance of the pump is prevented from being lowered
due to bubbles that would otherwise stick to the second electrode
and the electroosmotic member. Even if a portion of the gas
produced in the vicinity of the first electrode passes through the
electroosmotic member, it can still be discharged through the
downstream gas vent.
[0034] An upstream liquid passing member, for preventing foreign
matter from flowing into the electroosmotic member and for passing
the drive liquid therethrough when voltage is applied, should
preferably be disposed upstream from the electroosmotic member on
an upstream side of the fluid passage. Therefore, foreign matter
and bubbles are prevented from adhering to the surface of the
electroosmotic member, so that the performance of the
electroosmotic pump is maintained.
[0035] An upstream gas vent, for discharging gas produced in the
vicinity of the first electrode when voltage is applied thereto,
should preferably be disposed between the electroosmotic member and
the upstream liquid passing member. Therefore, gas is prevented
from sticking upstream from the electroosmotic member, so that the
performance of the electroosmotic pump is prevented from being
lowered.
[0036] An upstream liquid self-priming mechanism, for self-priming
the drive liquid, should preferably be disposed on an upstream side
of the fluid passage in contact with the electroosmotic member or
the first electrode. Therefore, the electroosmotic member can
reliably be supplied with drive liquid.
[0037] A downstream liquid self-priming mechanism, for self-priming
the drive liquid, should preferably be disposed on a downstream
side of the fluid passage in contact with the electroosmotic member
or the second electrode. Therefore, drive liquid, which has been
discharged from the electroosmotic member, can reliably be supplied
to any of various fluid devices that are connected to the
downstream side of the fluid passage.
[0038] The upstream liquid self-priming mechanism may be disposed
in contact with the electroosmotic member and the first electrode
for obtaining the same advantages as described above. The
downstream liquid self-priming mechanism may also be disposed in
contact with the electroosmotic member and the second electrode for
obtaining the same advantages as described above.
[0039] An electroosmotic pump according to the present invention
includes a first electrode and a second electrode, disposed
upstream and downstream, respectively, of an electroosmotic member
disposed inside a fluid passage, wherein when a voltage is applied
to the first electrode and the second electrode, drive liquid is
caused to flow in the fluid passage and through the electroosmotic
member, characterized in that an upstream liquid self-priming
mechanism for self-priming the drive liquid is disposed on an
upstream side of the fluid passage, in contact with the
electroosmotic member or the first electrode.
[0040] With the above arrangement, since the upstream liquid
self-priming mechanism and the electroosmotic member are held in
contact with each other, when the upstream liquid self-priming
mechanism is filled from the outside with the drive liquid, the
filled liquid quickly permeates the electroosmotic member from the
upstream liquid self-priming mechanism. Then, when a voltage is
applied to the electrodes, the drive liquid can reliably be
discharged from the electroosmotic member to a downstream side of
the fluid passage. As a result, the self-priming capability of the
electroosmotic pump is maintained, even if gas is present in the
vicinity of the first electrode.
[0041] An upstream liquid passing member for preventing foreign
matter from flowing into the electroosmotic member and for passing
the drive liquid therethrough when the voltage is applied, should
preferably be disposed upstream from the electroosmotic member on
an upstream side of the fluid passage. Therefore, foreign matter
and bubbles are prevented from adhering to the surface of the
electroosmotic member, so that the performance of the
electroosmotic pump is maintained.
[0042] An upstream gas vent, for discharging gas produced in the
vicinity of the first electrode when voltage is applied thereto,
should preferably be disposed between the electroosmotic member and
the upstream liquid passing member. Therefore, gas is prevented
from sticking upstream from the electroosmotic member, so that the
performance of the electroosmotic pump is prevented from being
lowered.
[0043] A downstream liquid self-priming mechanism for self-priming
the drive liquid should preferably be disposed on a downstream side
of the fluid passage, in contact with the electroosmotic member or
the second electrode. Therefore, the drive liquid that has been
discharged from the electroosmotic member can reliably be supplied
through the downstream liquid self-priming mechanism to any of
various fluid devices connected downstream from the electroosmotic
pump. Since self-priming mechanisms are disposed respectively at
upstream and downstream regions, the drive liquid is discharged
efficiently from the upstream region to the downstream region, and
further can be drawn efficiently from the downstream region toward
the upstream region.
[0044] The upstream liquid self-priming mechanism may be disposed
in contact with the electroosmotic member and the first electrode,
for obtaining the same advantages as described above. Further, the
downstream liquid self-priming mechanism may be disposed in contact
with the electroosmotic member and the second electrode, for
obtaining the same advantages as described above.
[0045] A downstream liquid passing member, for preventing gas from
passing downstream and passing the drive liquid therethrough,
should preferably be disposed downstream from the second electrode,
on a downstream side of the fluid passage. Consequently, even when
gas is produced near the second electrode by application of
voltage, the downstream liquid passing member disposed downstream
from the electroosmotic member allows the drive liquid to pass,
while preventing gas from passing therethrough. Accordingly, gas is
prevented from being introduced into any of various fluid devices,
such as a microfluid chip or the like, connected to the downstream
side of the fluid passage, and further, the electroosmotic pump can
accurately control the position of liquid that passes through the
fluid device, for example.
[0046] A downstream gas vent, for discharging gas produced in the
vicinity of the second electrode when voltage is applied thereto,
should preferably be disposed between the electroosmotic member and
the downstream liquid passing member. In this case, since gas
produced in the vicinity of the second electrode is discharged
through the downstream gas vent, when the electroosmotic pump is
operated over a prolonged period of time, performance of the pump
is prevented from being lowered by bubbles that would stick to the
second electrode and the electroosmotic member. Even if a portion
of the gas produced in the vicinity of the first electrode passes
through the electroosmotic member, it can be discharged through the
downstream gas vent.
[0047] Preferably, the liquid passing member is made of a
hydrophilic material, the gas pressure required for gas to pass
through the liquid passing member is 1 [kPa] or higher, and the
liquid passing member has a thickness of 3 [mm] or less along the
direction of the fluid passage.
[0048] Preferably, the gas vent is made of a hydrophobic material
disposed on a side wall of the fluid passage, a pressure under
which the drive liquid passes through the gas vent is smaller than
a maximum pressure of the drive liquid when the electroosmotic pump
is in operation, and the gas vent has a thickness of 3 [mm] or less
along the direction in which the gas passes.
[0049] Preferably, the liquid self-priming mechanism comprises a
self-priming member disposed in the vicinity of the electroosmotic
member along the fluid passage, and an air vent disposed alongside
of the self-priming member and having an impregnation pressure
different from that of the self-priming member, wherein the
self-priming member is self-primed with the drive liquid, and
supplies the drive liquid to the electroosmotic member. Further,
the air vent discharges air remaining upstream from the
electroosmotic member based on an impregnation pressure difference
between the self-priming member and the air vent.
[0050] The self-priming member should preferably be made of a
hydrophilic material, whereas the air vent should preferably be
made of a hydrophobic material.
[0051] Preferably, the electroosmotic member or the first electrode
and the upstream liquid passing member are spaced from each other
by an interval of 3 [mm] or less along the direction of the fluid
passage, and/or the electroosmotic member or the second electrode
and the downstream liquid passing member are spaced from each other
by an interval of 3 [mm] or less along the direction of the fluid
passage. Specifically, the interval between the electroosmotic
member or the first electrode and the upstream liquid passing
member, and/or the interval between the electroosmotic member or
the second electrode and the downstream liquid passing member, are
important parameters that affect the characteristics of the
electroosmotic pump. The interval at a time when surface tension is
more dominant than gravitation is about 3 [mm], and the interval at
a time when the resistance posed by the fluid passage is very large
is less than 1 [.mu.m]. Therefore, it is preferable for each of the
intervals to be set to an appropriate value, lying within a range
from an upper value of 3 [mm] to a lower value of 1 [.mu.m] (1
[.mu.m] to 3 [mm]), in terms of the characteristics of the
electroosmotic pump.
[0052] Particularly, if the upstream liquid passing member and the
upstream gas vent are disposed in confronting relation to the
electroosmotic member and the first electrode, then the interval
between the electroosmotic member or the first electrode and the
upstream liquid passing member, as well as the interval between the
electroosmotic member or the first electrode and the upstream
liquid passing member, should preferably be set to a value within
the above range. Similarly, if the downstream liquid passing member
and the downstream gas vent are disposed in confronting relation to
the electroosmotic member and the second electrode, the interval
between the electroosmotic member or the second electrode and the
downstream liquid passing member, as well as the interval between
the electroosmotic member or the second electrode and the
downstream liquid passing member, should preferably be set to a
value within the above range.
[0053] A drive liquid absorbing member, which can closely contact
with the upstream liquid self-priming mechanism and the
electroosmotic member or the first electrode, and which is made of
a hydrophilic material, should preferably be disposed between the
upstream liquid self-priming mechanism and the electroosmotic
member or the first electrode. In addition, or alternatively, a
drive liquid absorbing member, which can closely contact with the
downstream liquid self-priming mechanism and the electroosmotic
member or the second electrode, and which is made of a hydrophilic
material, should preferably be disposed between the downstream
liquid self-priming mechanism and the electroosmotic member or the
second electrode.
[0054] If the upstream liquid self-priming mechanism is made of a
rigid material, then since the drive liquid absorbing member
closely contacts with the surface of the upstream liquid
self-priming mechanism and to the surface of the electroosmotic
member or the first electrode, the drive liquid that has been
introduced into the upstream liquid self-priming mechanism by way
of self-priming can efficiently be absorbed by the drive liquid
absorbing member, and be supplied quickly to the electroosmotic
member. The drive liquid absorbing member should desirably be made
of a pliable, water-retentive, water-absorbing material, which is
sandwiched between the upstream liquid self-priming mechanism and
the electroosmotic member or the first electrode, in order to
increase contact of the drive liquid absorbing member. Furthermore,
since the drive liquid absorbing member also functions as a cushion
between the upstream liquid self-priming mechanism and the
electroosmotic member or the first electrode, the components can be
assembled efficiently.
[0055] If a drive liquid absorbing member is disposed between the
downstream liquid self-priming mechanism and the electroosmotic
member or the second electrode, wherein the downstream liquid
self-priming mechanism is made of a rigid material, then since the
drive liquid absorbing member closely contacts with the surface of
the downstream liquid self-priming mechanism, as well as to the
surface of the electroosmotic member or the second electrode, the
drive liquid that has been introduced into the downstream liquid
self-priming mechanism by way of self-priming can efficiently be
absorbed by the drive liquid absorbing member and be supplied
quickly to the electroosmotic member. In this case, the drive
liquid absorbing member should desirably be made of a pliable,
water-retentive, water-absorbing material, which is sandwiched
between the downstream liquid self-priming mechanism and the
electroosmotic member or the second electrode, in order to increase
contact of the drive liquid absorbing member. Furthermore, since
the drive liquid absorbing member also functions as a cushion
between the downstream liquid self-priming mechanism and the
electroosmotic member or the second electrode, the components can
be assembled efficiently.
[0056] In each of the inventions described above, the fluid passage
should preferably be defined inside a pump casing, which
accommodates therein the electroosmotic member, the first
electrode, and the second electrode. The fluid passage should
preferably have an upstream inlet and a downstream outlet, which
are defined in one surface of the pump casing. Therefore, the
electroosmotic pump can be easily installed on an installation
surface such as a board or the like, and can be reduced in overall
height. Since the inlet and the outlet are defined in one surface,
gas vents can be disposed on the opposite surface. Consequently,
the electroosmotic pump according to the present invention is
suitable for use as a small-size surface-mounted pump, installed
within electronic devices, for example.
[0057] A liquid feeding device according to the present invention
comprises the above electroosmotic pump, and a liquid container
filled with a liquid, wherein liquid stored in the liquid container
is discharged by means of the electroosmotic pump. When a voltage
is applied to the first and second electrodes of the electroosmotic
pump, liquid stored in the liquid container can be supplied from
the liquid container by operation of the electroosmotic pump. The
liquid can thus be supplied by means of a simple structure. When
voltage is applied to the first and second electrodes, while the
liquid is introduced by way of self-priming utilizing the upstream
liquid self-priming mechanism, the liquid can be supplied from the
liquid container through the electroosmotic member as well as from
the upstream liquid self-priming mechanism. As a consequence,
liquid can be supplied efficiently. If the liquid in the liquid
feeding device is methanol or methanol water, i.e., methanol
diluted with water, then the liquid feeding device may be used
suitably as a liquid fuel supply cartridge, for supplying methanol
or methanol water to a fuel cell system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] FIG. 1 is a cross-sectional view of an electroosmotic pump
according to a first embodiment of the present invention;
[0059] FIG. 2 is a partial cross-sectional view, illustrating a
self-priming function performed by a first self-priming
mechanism;
[0060] FIG. 3 is a cross-sectional view of an electroosmotic pump
according to a second embodiment of the present invention;
[0061] FIG. 4 is an enlarged partial cross-sectional view, showing
a combined interfitting of a large-diameter portion and a
small-diameter portion, as illustrated in FIG. 3;
[0062] FIG. 5 is an enlarged partial cross-sectional view showing a
bonded combination of a large-diameter portion and a small-diameter
portion, as illustrated in FIG. 3;
[0063] FIG. 6 is a cross-sectional view of an electroosmotic pump
according to a third embodiment of the present invention;
[0064] FIG. 7 is a cross-sectional view of an electroosmotic pump
according to a fourth embodiment of the present invention;
[0065] FIG. 8 is a partial cross-sectional view showing a structure
of a gas vent illustrated in FIG. 7;
[0066] FIG. 9 is a vertical cross-sectional view taken along line
IX-IX of FIG. 8;
[0067] FIG. 10 is a vertical cross-sectional view taken along line
X-X of FIG. 8;
[0068] FIG. 11 is a partial cross-sectional view showing another
structure of the gas vent illustrated in FIG. 7;
[0069] FIG. 12 is a partial cross-sectional view showing still
another structure of the gas vent illustrated in FIG. 7;
[0070] FIG. 13 is a partial cross-sectional view showing a
structure of a bubble isolator illustrated in FIG. 7;
[0071] FIG. 14 is a partial cross-sectional view showing another
structure of the bubble isolator illustrated in FIG. 7;
[0072] FIG. 15 is a cross-sectional view of an electroosmotic pump
according to a fifth embodiment of the present invention;
[0073] FIG. 16 is a cross-sectional view of an electroosmotic pump
according to a sixth embodiment of the present invention;
[0074] FIG. 17 is a cross-sectional view of an electroosmotic pump
according to a seventh embodiment of the present invention;
[0075] FIG. 18 is a partial cross-sectional view showing another
structure of a self-priming mechanism illustrated in FIG. 17;
[0076] FIG. 19 is a partial cross-sectional view showing still
another structure of the self-priming mechanism illustrated in FIG.
17;
[0077] FIG. 20 is a partial cross-sectional view showing yet
another structure of the self-priming mechanism illustrated in FIG.
17;
[0078] FIG. 21 is a vertical cross-sectional view taken along line
XXI-XXI of FIG. 20;
[0079] FIG. 22 is a cross-sectional view of an electroosmotic pump
according to an eighth embodiment of the present invention;
[0080] FIG. 23 is a cross-sectional view showing another structure
of the electroosmotic pump illustrated in FIG. 22;
[0081] FIG. 24 is a cross-sectional view of an electroosmotic pump
according to a ninth embodiment of the present invention;
[0082] FIG. 25 is a cross-sectional view of an electroosmotic pump
according to a tenth embodiment of the present invention;
[0083] FIG. 26 is a cross-sectional view of an electroosmotic pump
according to an eleventh embodiment of the present invention;
[0084] FIG. 27 is a cross-sectional view of an electroosmotic pump
according to a twelfth embodiment of the present invention;
[0085] FIG. 28 is a cross-sectional view showing another structure
of the electroosmotic pump illustrated in FIG. 27;
[0086] FIG. 29 is a cross-sectional view of an electroosmotic pump
according to a thirteenth embodiment of the present invention;
[0087] FIG. 30 is a cross-sectional view showing another structure
of the electroosmotic pump illustrated in FIG. 28;
[0088] FIG. 31 is a cross-sectional view of an electroosmotic pump
according to a fourteenth embodiment of the present invention;
[0089] FIG. 32 is a cross-sectional view showing another structure
of the electroosmotic pump illustrated in FIG. 31;
[0090] FIG. 33 is a cross-sectional view showing still another
structure of the electroosmotic pump illustrated in FIG. 31;
[0091] FIG. 34 is a cross-sectional view showing yet another
structure of the electroosmotic pump illustrated in FIG. 31;
[0092] FIG. 35 is a cross-sectional view of an electroosmotic pump
according to a fifteenth embodiment of the present invention;
[0093] FIG. 36 is a cross-sectional view of an electroosmotic pump
according to a sixteenth embodiment of the present invention;
[0094] FIG. 37 is a cross-sectional view of a liquid feeding
device, which incorporates the electroosmotic pump according to the
fifteenth embodiment;
[0095] FIG. 38 is a partial cross-sectional view showing a
conventional electroosmotic pump;
[0096] FIG. 39 is a partial cross-sectional view showing another
conventional electroosmotic pump; and
[0097] FIG. 40 is a partial cross-sectional view showing an
electroosmotic pump devised by the present applicant.
BEST MODE FOR CARRYING OUT THE INVENTION
[0098] An electroosmotic pump 10A according to a first embodiment
is a small-sized pump, having a size ranging from several [mm] to
several [cm], so that it can be installed on a microfluid chip or
in a small-size electronics device, for use in biotechnology and
analytic chemistry. As shown in FIG. 1, the electroosmotic pump 10A
basically comprises a pump casing 12, an electroosmotic member 16
disposed in a fluid passage 14 defined in the pump casing 12, an
inlet electrode (first electrode) 18, and an outlet electrode
(second electrode) 20.
[0099] The pump casing 12 is made of a plastic material that is
resistant to a drive liquid, such as an electrolytic solution or
the like, which passes through the fluid passage 14. The pump
casing 12 may also be made of ceramics, glass, or a metal material
having an electrically insulated surface. The pump casing 12
includes a large-diameter portion 22 in which the electroosmotic
member 16, the inlet electrode 18, and the outlet electrode 20 are
disposed, and a small-diameter portion 24, which can be connected
to a fluid device such as a microfluid chip or the like, not shown.
The electrolytic solution passes through the fluid passage 14 from
the right (the large-diameter portion 22) and toward the left (the
small-diameter portion 24) in FIG. 1.
[0100] The electroosmotic member 16 is disposed so as to divide the
fluid passage 14 into a region upstream (right in FIG. 1) from the
electroosmotic member 16, thus forming an inlet chamber 26, and a
region downstream from the electroosmotic member 16, serving as an
outlet chamber 28. The electroosmotic member 16 is made of porous
ceramics or glass fibers. The electroosmotic member 16 has a
hydrophilic nature, such that when the inlet chamber 26 is supplied
with drive liquid, the electroosmotic member 16 absorbs and is
impregnated with the liquid, and then discharges the drive liquid
into the outlet chamber 28.
[0101] The inlet electrode 18 is disposed in the inlet chamber 26
in contact with a surface of the electroosmotic member 16, and has
a plurality of pores 30 defined therein along the axial direction
of the fluid passage 14. The outlet electrode 20 is disposed in the
outlet chamber 28 in contact with a surface of the electroosmotic
member 16, and has a plurality of pores 30 defined therein along
the axial direction of the fluid passage 14. The inlet electrode 18
and the outlet electrode 20 are electrically connected to a DC
power supply 34.
[0102] In FIG. 1, the inlet electrode 18 serves as a positive
electrode and the outlet electrode 20 as a negative electrode, on
the assumption that the electroosmotic member 16 is negatively
charged. However, if the electroosmotic member 16 is positively
charged, then the inlet electrode 18 may serve as a negative
electrode while the outlet electrode 20 serves as a positive
electrode. In FIG. 1, the electrodes 18, 20 are disposed on
surfaces of the electroosmotic member 16. However, the electrodes
18, 20 are not limited to such a layout, and may be disposed near
the electroosmotic member 16, out of contact therewith. In FIG. 1,
the DC power supply 34 is electrically connected to the inlet
electrode 18 and the outlet electrode 20, and applies a DC voltage
to the electrodes 18, 20. However, the voltage applied to the
electrodes 18, 20 is not limited to being a DC voltage. Instead, a
pulsed power supply, not shown, may be employed in place of the DC
power supply 34, for applying a pulsed voltage to the electrodes
18, 20.
[0103] In the electroosmotic pump 10A, drive liquid is supplied to
the inlet chamber 26 and permeates through the pores 30 of the
electroosmotic member 16. When the DC power supply 34 applies a DC
voltage to the electrodes 18, 20, the drive liquid through the
electroosmotic member 16 moves in a direction from the inlet
electrode 18 toward the outlet electrode 20, and is discharged
through the pores 32 into the outlet chamber 28.
[0104] The electroosmotic pump 10A also has a bubble isolator
(downstream liquid passing member) 40 disposed in the outlet
chamber 28 downstream from the outlet electrode 20, a gas vent
(downstream gas vent) 42 disposed in a side wall of the pump casing
12 in the vicinity of the outlet electrode 20, and a gas vent
(upstream gas vent) 44 disposed in a side wall of the pump casing
12 in the vicinity of the inlet electrode 18.
[0105] The bubble isolator 40 comprises a hydrophilic membrane made
of glass fibers, or a polyamide-based synthetic polymeric material
such as hydrophilic Nylon (registered trademark). The bubble
isolator 40 passes the drive liquid, which has been discharged
downstream through the pores 32 from the electroosmotic member 16,
while preventing gas and foreign matter in the outlet chamber 28
from passing therethrough. The gas vent 42 comprises a hydrophobic
gas-permeable membrane or sheet made of polytetrafluoroethylene
(PTFE) or the like, wherein gas in the outlet chamber 28 is
discharged through the gas vent 42 out of the pump casing 12. The
gas vent 44 comprises a hydrophobic gas-permeable membrane, similar
to the gas vent 42, wherein gas in the inlet chamber 26 is
discharged through the gas vent 44 out of the pump casing 12.
[0106] In the electroosmotic pump 10A, the drive liquid, such as an
electrolytic solution (aqueous solution) or the like, permeates the
electroosmotic member 16. When the DC power supply 34 applies a DC
voltage to the electrodes 18, 20, hydrogen gas is produced in the
vicinity of the outlet electrode 20 whereas oxygen gas is produced
in the vicinity of the inlet electrode 18, as a result of an
electrochemical reaction that occurs in the drive liquid near the
electrodes 18, 20. If the current flowing between the electrodes
18, 20 is 1 [mA], for example, then hydrogen gas is produced at a
rate of 7.86 [.mu.L/min], whereas oxygen gas is produced at a rate
of 3.93 [.mu.L/min].
[0107] The solubility of the oxygen gas is 0.031, whereas the
solubility of the hydrogen gas is 0.018, when the aqueous solution
(or water) has a temperature of 20 [.degree. C.]. Even if the
solubility of the oxygen and hydrogen gases in the aqueous solution
is nil at the time the electroosmotic pump 10A is actuated, when
the ratio of the amount of gas produced (volume at one atmospheric
pressure) to the flow rate of the aqueous solution exceeds 3.1 [%]
(oxygen) and 1.8 [%] (hydrogen), the gas concentration in the
aqueous solution exceeds the solubility, thereby causing oxygen gas
bubbles to be produced in the inlet chamber 26 near the electrode
18, and also causing hydrogen gas bubbles to be produced in the
outlet chamber 28 near the electrode 20. More specific numerical
values shall be indicated below. If the pump flow rate is 100
[.mu.L/min], then oxygen gas bubbles are produced at the inlet
electrode 18 at a current of 790 [.mu.A] or greater, and hydrogen
gas bubbles are produced at the outlet electrode 20 at a current of
229 [.mu.A] or greater.
[0108] When such bubbles stick to the surfaces of the electrodes
18, 20 and the electroosmotic member 16, the bubbles tend to
prevent the aqueous solution from being supplied to and discharged
from the electroosmotic member 16. Furthermore, the electric field
distribution around the electroosmotic member 16 becomes distorted,
resulting in a reduction in performance of the electroosmotic pump
10A. When the bubbles flow downstream within the fluid passage 14,
the bubbles also are introduced into a fluid pressure device, such
as a microfluid chip or the like, connected downstream from the
electroosmotic pump 10A. Thus, the electroosmotic pump 10A fails to
appropriately control the displacement of the minute fluid within
the fluid pressure device, or various sensors connected downstream
from the electroosmotic pump 10A may be adversely affected during
operation.
[0109] In the electroosmotic pump 10A, a minimum bubble point of
the bubble isolator 40 and a minimum water breakthrough point of
the gas vents 42, 44 are set to sufficiently large levels, compared
with the pressure at which the aqueous solution is driven. The
minimum bubble point refers to the minimum pressure value required
for bubbles (hydrogen gas or oxygen gas) to pass through the bubble
isolator 40, which has been wetted by the aqueous solution. The
bubbles also may comprise gas different from the hydrogen gas and
the oxygen gas, depending on the type of drive liquid. The minimum
water breakthrough point refers to the minimum pressure value
required for the aqueous solution to leak out of the chambers 26,
28 through the gas vents 42, 44.
[0110] While the pump is in operation, the pressure in the outlet
chamber 28 has a difference (positive pressure) ranging from
several [kPa] to several hundreds [kPa] from the external pressure.
Therefore, bubbles that accumulate in the outlet chamber 28 are
discharged out of the electroosmotic pump 10A through the gas vent
42. When the aqueous solution passes through the bubble isolator
40, it develops a certain pressure loss. Pressure loss can be
reduced by selecting an appropriate fluid passage resistance for
the bubble isolator 40.
[0111] Therefore, bubbles can be discharged out of the
electroosmotic pump 10A through the gas vents 42, 44 rather than
passing downstream from the electroosmotic pump 10A.
[0112] The bubble isolator 40 is designed to satisfy two conditions
with respect to the outlet pressure, the minimum bubble point, and
the fluid passage resistance, at a time when the pump is in
operation, such that (1) the minimum bubble point should be greater
than the maximum pressure (the maximum pressure on the outlet side
of the electroosmotic pump 10A) of the aqueous solution discharged
from the electroosmotic member 16 (minimum bubble point>maximum
pressure of the aqueous solution), and (2) the pressure loss across
the bubble isolator 40 at the maximum flow rate of the aqueous
solution should be sufficiently smaller than the maximum pressure
of the aqueous solution discharged from the electroosmotic member
16.
[0113] A specific structural example shall be described below.
[0114] The bubble isolator 40 comprises a membrane made of
hydrophilic Nylon (registered trademark) (pore diameter: 0.2
[.mu.m], membrane thickness: 127 [.mu.m]). The minimum bubble point
of the bubble isolator 40 is 340 [kPa], and the rate at which the
aqueous solution passes through the bubble isolator 40 is 170
[.mu.l/(mincm.sup.2kPa)]. The gas vents 42, 44 comprise a membrane
of PTFE (pore diameter: 0.2 [.mu.m], membrane thickness: 139
[.mu.m]). The water breakthrough point of the gas vents 42, 44 is
280 [kPa], and the rate at which gas passes through the gas vents
42, 44 is 28 [ml/(mincm.sup.2kPa)].
[0115] The pressure loss developed in the aqueous solution across
the bubble isolator 40, and the cross-sectional area of the gas
vent 42 required to discharge hydrogen gas, shall be described
below in specific detail.
[0116] If it is assumed that the diameter of the electroosmotic
member 16 is 7 [mm], the flow rate of the aqueous solution is 200
[.mu.L/min], the rate at which hydrogen gas is produced is 100
[.mu.L/min], and the pressure in the outlet chamber 28 is 50 [kPa].
Further, the pressure loss developed in the aqueous solution across
the bubble isolator 40 is 3 [kPa], and the cross-sectional area of
the gas vent 42 is 0.007 [mm.sup.2]
[0117] As described above, the pressure loss developed in the
aqueous solution across the bubble isolator 40 is about several
[kPa], which is a problem-free numerical value from the standpoint
of general pump characteristics of the electroosmotic pump.
[0118] The gas vent 42 is capable of discharging hydrogen gas from
the electroosmotic pump through a cross-sectional area of about
0.007 [mm.sup.2]. If the cross-sectional area is small, then the
aqueous solution is prevented from losses caused by evaporation
within the electroosmotic pump 10A. In the above specific example,
since the thicknesses of the bubble isolator 40 and the gas vent 42
are smaller than 150 [.mu.m], the size of the electroosmotic pump
10A remains essentially unchanged, even when these components are
added.
[0119] If the diameter of the space (outlet chamber 28) defined by
the bubble isolator 40, the electroosmotic member 16, and the inner
wall of the pump casing 12 is 2 to 3 [mm] or less, then surface
tension is more dominant on the aqueous solution than gravitation.
Therefore, the electroosmotic pump 10A is orientation-free, and is
not susceptible to gravitational forces no matter what attitude the
electroosmotic pump 10A is placed in.
[0120] The bubble isolator 40 also is effective to prevent air from
flowing from outside back into the inlet chamber 26 and the outlet
chamber 28 through the gas vents 42, 44, and to prevent foreign
matter which has entered the electroosmotic pump 10A from being
discharged downstream, when the pressure of the aqueous solution
drops downstream from the system including the electroosmotic pump
10A and the microfluid chip.
[0121] As described above, the electroosmotic pump 10A is a
small-sized pump, which can be installed on a microfluid chip or a
small-sized electronics device, not shown. The inlet chamber 26 has
an inside diameter of about several [mm] or less. Therefore, large
forces due to surface tension act on the electrolytic solution
flowing through the fluid passage 14. When a supply line for the
electrolytic solution, or a cartridge or tank filled with the
electrolytic solution, is simply connected to the inlet side (on
the right in FIG. 1) of the electroosmotic pump 10A, air remains
trapped within the inlet chamber 26 when the electrolytic solution
is supplied, thus possibly preventing the electroosmotic pump 10A
from being activated normally.
[0122] Accordingly, the electroosmotic pump 10A includes a
self-priming mechanism 50 disposed in the inlet chamber 26. The
self-priming mechanism 50 comprises a liquid suction member
(self-priming member) 52, having a tip end thereof held in contact
with the electroosmotic member 16 through the inlet electrode 18,
and an air-bleeding path (air bleeder) 56 defined between a
surrounding member 54 that surrounds the sides of the liquid
suction member 52 and the inner wall of the pump casing 12.
[0123] The liquid suction member 52 is made of a hydrophilic
material, such as porous ceramics or glass fibers, which are highly
permeable to the electrolytic solution. If the liquid suction
member 52 is made of glass fibers, then a surrounding member 54,
which is made of the same material as the pump casing 12, serves as
a side wall, preventing the glass fibers from being deformed in
shape. The surrounding member 54 may be dispensable if the liquid
suction member 52 is made of a material, such as a porous ceramic,
which is not deformed in shape when placed in the pump casing
12.
[0124] The air-bleeding path 56 is constructed as a passage that
has a lower impregnation pressure with respect to the electrolytic
solution than the liquid suction member 52. The air-bleeding path
56 may simply be a gas-bleeding passage, or it may be filled with a
less-impregnation hydrophilic material, or with a hydrophobic
material.
[0125] When the electroosmotic pump 10A is activated, the liquid
suction member 52 is supplied with the drive liquid from outside of
the electroosmotic pump 10A. The supplied liquid permeates the
liquid suction member 52 and wets the surface of the electroosmotic
member 16, which is held in contact with the liquid suction member
52. As a result, the drive liquid seeps spontaneously into the
electroosmotic member 16 due to capillary action, until the liquid
reaches the surface of the outlet electrode 20 on the side of the
outlet chamber 28. The electroosmotic pump 10A is now readied for
activation.
[0126] The self-priming mechanism 50 must satisfy three conditions,
such that (1) it should be capable of wetting the surface of the
electroosmotic member 16 with the drive liquid, (2) it should be
able to discharge air in the inlet chamber 26 out of the inlet
chamber 26, and (3) the time required for (1) and (2) should be
equal to or shorter than the activation time required by the
electroosmotic pump 10A.
[0127] FIG. 2 is a schematic cross-sectional view illustrating
principles of a process for supplying the drive liquid from the
self-priming mechanism 50 to the electroosmotic member 16. In FIG.
2, the pump casing 12, the inlet electrode 18, the outlet electrode
20, and the surrounding member 46 are omitted from illustration.
The liquid suction member 52 and the air-bleeding path 56 have
respective ends immersed within an electrolytic solution 60, which
forms the drive liquid and is contained in a casing 62.
[0128] The impregnation characteristics of the electrolytic
solution 60 in the porous medium of the liquid suction member 52
and in the air-bleeding path 56 are determined by the surface
energy .gamma..sub.SO of the porous medium, the surface energy
.gamma..sub.SL of the interface between the porous medium and the
electrolytic solution 60, the surface energy .gamma. of the
electrolytic solution 60, and the internal surface area of the
porous medium. If pores (having a diameter D) in the porous medium
are provided in a uniform density along the direction from the
surface of the electrolytic solution 60 toward the electroosmotic
member 16, then the impregnation pressure P of the electrolytic
solution 60 in the liquid suction member 52 is determined by a
reduction in the surface energy per unit length, and is given by
the following equation (2):
P=4.gamma..times.(.gamma..sub.SL-.gamma..sub.SO)/D=4.gamma. cos
.theta./D (2)
where cos .theta.=(.gamma..sub.SL-.gamma..sub.SO).
[0129] If the surface tension of water (electrolytic solution) is
.gamma.=73 [mN/m], D=10 [.mu.m], and .theta.=0, then the
impregnation pressure P is about 28 [kPa]. If D=100 .mu.m, then P=3
[kPa].
[0130] In FIG. 2, the liquid suction member 52 disposed in the
inlet chamber 26 (see FIG. 1) is constructed as a porous body,
having pores with a diameter D=10 [.mu.m], and the air-bleeding
path 56 is constructed as a porous body, having pores with a
diameter D=100 [.mu.m]. The porous bodies are placed in the casing
62 containing the electrolytic solution 60.
[0131] The electrolytic solution 60 seeps upwardly into the liquid
suction member 52 and the air-bleeding path 56, developing a
pressure buildup in the liquid suction member 52 and the
air-bleeding path 56. Due to the difference between the
impregnation pressure (28 [kPa]) in the liquid suction member 52
and the impregnation pressure (3 [kPa]) in the air-bleeding path
56, the electrolytic solution 60 that permeates the liquid suction
member 52 pushes the electrolytic solution 60 that permeates the
air-bleeding path 56 through air, and reaches the surface of the
electroosmotic member 16 earlier than the electrolytic solution 60
that permeates the air-bleeding path 56. As a result, air in the
vicinity of the surface of the electroosmotic member 16 flows into
the air-bleeding path 56, developing a positive pressure of about 3
kPa in the air-bleeding path 56.
[0132] Therefore, the self-priming mechanism 50 satisfies three
conditions, from the standpoints of its self-priming capability and
discharging of air, such that (1) the liquid suction member 52 with
the higher impregnation pressure P should allow the electrolytic
solution 60 to reach the surface of the electroosmotic member 16 on
the side of the inlet chamber 26, (2) air present in the inlet
chamber 26 should be discharged out of the inlet chamber 26 from
the air-bleeding path 56 with the lower impregnation pressure P (3
[kPa]), and (3) a positive pressure determined by the lower
impregnation pressure P (3 [kPa]) should be developed in the
air-bleeding path 56.
[0133] According to condition (1), the electroosmotic member 16 can
be supplied with the electrolytic solution 60, such that the
surface of the electroosmotic member 16 is continuously supplied
with the electrolytic solution 60 at the time the electroosmotic
pump 10A starts operating. According to the condition (2), the
surface of the electroosmotic member 16 can be wetted by the
electrolytic solution 60, while permeation of the electrolytic
solution 60 is not obstructed by air in the inlet chamber 26.
According to the condition (3), the self-priming mechanism 50 can
generate a pressure required to discharge gas generated in the
inlet chamber 26 (including oxygen gas generated in the vicinity of
the electrode 18) out of the pump casing 12, so that the pressure
required to discharge oxygen gas generated at the electrode 18 from
the gas vent 44 can be generated at the time that the
electroosmotic pump 10A is self-primed.
[0134] The speed of operation of the self-priming mechanism 50 at
the time the electroosmotic pump 10A is activated shall be
described below. The time required until the surface of the
electroosmotic member 16 on the side of the inlet chamber 26 is
wetted by the electrolytic solution 60 serves as a rough indication
of the operating speed of the self-priming mechanism 50.
[0135] The motion of the electrolytic solution 60 within the liquid
suction member 52, which acts as a capillary tube, is determined by
the drive force F due to surface tension (F=2.pi.R.gamma. cos
.theta., R: the diameter of the liquid suction member 52), and the
pressure determined by the viscous friction and the gravitational
force within the capillary tube. If the pressure term due to
gravitational force is sufficiently smaller than the drive force
due to surface tension (i.e., if the impregnation pressure is
sufficiently low), such as when the distance that the solution
permeates through the capillary tube is small or when the capillary
tube is placed horizontally, then since the gravitational term can
be ignored, the relationship between the distance Z over which the
electrolytic solution 60 moves, and the time t that it takes the
electrolytic solution 60 to move in the liquid suction member 52,
is given by the following equation (3):
Z.sup.2=.gamma.R cos .theta..times.t/(2.eta.) (3)
where t represents the time in which the electrolytic solution 60
moves in the liquid suction member 52, and .eta. the viscous
modulus of the liquid suction member 52.
[0136] If Z=20 [mm] (the distance from an upstream connection port
of the electroosmotic pump 10A to the surface of the electroosmotic
member 16), .gamma.=73 [mN/m], R=10 [.mu.m], .theta.=0, and
.eta.=0.001 [Pas] in equation (3), then t.apprxeq.1 [s]. Since t
becomes longer as R becomes smaller, a tradeoff is required between
the speed of operation of the self-priming mechanism 50 and the
impregnation pressure within liquid suction member 52.
[0137] The electroosmotic pump 10A according to the first
embodiment is constructed as described above. Operations and
advantages of the electroosmotic pump 10A shall now be described
below with reference to FIGS. 1 and 2.
[0138] The upstream side of the electroosmotic pump 10A and a tank
or cartridge, not shown, are connected to each other, wherein the
self-priming mechanism 50 is supplied with the electrolytic
solution from the tank or cartridge. Since the liquid suction
member 52 has an upstream end projecting from the pump casing 12,
when the tank or cartridge and the upstream side of the
electroosmotic pump 10A are connected to each other, the upstream
end of the liquid suction member 52 is immersed within the
electrolytic solution 60 in the tank or cartridge.
[0139] The electrolytic solution 60 permeates the liquid suction
member 52, travels downstream in the liquid suction member 52, and
also enters into the air-bleeding path 56. When the electrolytic
solution 60 in the liquid suction member 52 reaches the surface of
the electrode 18 earlier than the electrolytic solution 60
traveling through the air-bleeding path 56, the electrolytic
solution 60 in the liquid suction member 52 permeates the
electroosmotic member 16 through the pores 30 in the electrode 18.
At the same time, the electrolytic solution 60 develops a pressure
buildup in the inlet chamber 26. Inasmuch as the impregnation
pressure in the liquid suction member 52 is higher than the
impregnation pressure in the air-bleeding path 56, air near the
electrode 28 enters the air-bleeding path 56 and is discharged
while pushing the electrolytic solution 60 in the air-bleeding path
56, or is discharged through the air-bleeding path 56.
[0140] The electrolytic solution 60 that has permeated the
electroosmotic member 16 quickly seeps from the inlet electrode 18
toward the outlet electrode 20, thereby filling the electroosmotic
member 16.
[0141] When the DC power supply 34 applies a DC voltage to the
electrodes 18, 20, the electrolytic solution 60 in the
electroosmotic member 16 moves toward the outlet electrode 20,
based on the electric field generated between the electrodes 18,
20, and is discharged through the pores 32 of the electrode 20 into
the outlet chamber 28.
[0142] The electrolytic solution 60 that has been discharged into
the outlet chamber 28 is supplied through the bubble isolator 40 to
a fluid device such as a microfluid chip, not shown, connected to
the downstream side of the fluid passage 14.
[0143] Oxygen gas bubbles produced near the electrode 18 by an
electrochemical reaction when the DC voltage is applied are
discharged through the gas vent 44, and hydrogen gas bubbles
produced near the electrode 20 are discharged through the gas vent
42.
[0144] In FIG. 1, the upstream end of the liquid suction member 52
projects from the pump casing 12. However, the liquid suction
member 52 can be supplied with electrolytic solution 60 from the
tank or cartridge regardless of whether the upstream ends of the
liquid suction member 52 and the pump casing 12 are aligned in
position with each other, or whether the upstream end of the liquid
suction member 52 is located within the pump casing 12.
[0145] With the electroosmotic pump 10A according to the first
embodiment, therefore, even when hydrogen gas is produced near the
outlet electrode 20 by application of the DC voltage, the bubble
isolator 40 disposed downstream from the electroosmotic member 16
allows the drive liquid and the electrolytic solution 60 to pass
therethrough, while preventing hydrogen gas from passing.
Accordingly, hydrogen gas is prevented from being introduced into
the fluid device such as a microfluid chip, not shown, connected to
the downstream side of the fluid passage 14. Further, the
electroosmotic pump 10A can accurately control the position of the
liquid that passes through the fluid device.
[0146] Since hydrogen gas produced in the vicinity of the outlet
electrode 20 is discharged through the gas vent 42, when the
electroosmotic pump 10A is operated over a long period of time, the
pump performance is prevented from being lowered by bubbles that
would otherwise stick to the outlet electrode 20 and to the
electroosmotic member 16. Even if a portion of the oxygen gas
produced in the vicinity of the inlet electrode 18 passes through
the electroosmotic member 16, it can be discharged through the gas
vent 42.
[0147] The gas vent 44 is effective at preventing oxygen gas from
sticking upstream from the electroosmotic member 16 and the inlet
electrode 18, so that performance of the electroosmotic pump 10A is
prevented from being lowered.
[0148] Since the liquid suction member 52 of the self-priming
mechanism 50 and the electroosmotic member 16 are held in contact
with each other, when the liquid suction member 52 is filled with
electrolytic solution 60 from the outside, the filled electrolytic
solution 60 quickly permeates the electroosmotic member 16 through
the liquid suction member 52. When the DC voltage is then applied
to the electrodes 18, 20, the drive liquid and the electrolytic
solution 60 can reliably be discharged from the electroosmotic
member 16 toward the downstream side of the fluid passage 14. As a
result, a self-priming capability of the electroosmotic pump 10A is
maintained, even if air is present in the vicinity of the inlet
electrode 18.
[0149] In the above description, it is desirable for the liquid
suction member 52 to be held in contact with the electroosmotic
member 16, from the standpoint of self-priming the drive liquid
(the electrolytic solution 60). If the wettability between the
inlet electrode 18 and the electrolytic solution is good, then the
electroosmotic member 16 and the liquid suction member 52 can be
held in contact with the inlet electrode 18 interposed
therebetween, i.e., the liquid suction member 52 and the inlet
electrode 18 can be held in contact with each other. Furthermore,
both the electroosmotic member 16 and the inlet electrode 18 can be
held in contact with the liquid suction member 52.
[0150] Assuming that the bubble isolator 40 is made of a
hydrophilic material, the gas pressure required for gas to pass
through the bubble isolator 40 (the minimum bubble point) is 1
[kPa] or higher, and the thickness of the bubble isolator 40 along
the axial direction of the fluid passage 14 is 3 [mm] or less, then
hydrogen gas produced in the vicinity of the electrode 20 is
prevented from flowing downstream along the fluid passage 14,
according to the actual pump characteristics (dimensions and
pressure characteristics) which the present embodiment is concerned
with.
[0151] If the gas vent 42 is made of a hydrophobic material, the
pressure under which the drive liquid passes through the gas vent
42 is set at a level lower than the maximum pressure of the drive
liquid when the pump is in operation, and the thickness of the gas
vent 42 along the direction in which the gas passes in the fluid
passage 14 is 3 [mm] or less, then hydrogen gas produced in the
vicinity of the electrode 20 can be discharged efficiently.
[0152] In the electroosmotic pump 10A according to the first
embodiment, an electrolytic solution 60 has been described
primarily as the drive liquid. However, other liquids may be used
as the drive liquid. In this case, when a DC voltage is applied to
the electrodes 18, 20, gas bubbles of a component peculiar to the
other liquid are produced in the vicinity of the electrodes 18,
20.
[0153] In the electroosmotic pump 10A, the electrodes 18, 20 are
shaped as electrodes having pores 30, 32 defined therein. However,
wire-shaped electrodes, or electrodes in the form of a porous body
whose surface is evaporated with a metal, may also be employed. The
electrodes 18, 20 should preferably be made of an electrically
conductive material, such as platinum, carbon, silver or the
like.
[0154] The inlet electrode 18 serves as a positive electrode and
the outlet electrode 20 serves as a negative electrode, on the
assumption that the electroosmotic member 16 is negatively charged.
However, if the electroosmotic member 16 is positively charged,
then the inlet electrode 18 may serve as a negative electrode while
the outlet electrode 20 serves as a positive electrode, wherein the
above operations and advantages can also be achieved.
[0155] Although the DC voltage is applied to the electrodes 18, 20,
a pulsed voltage may also be applied to the electrodes 18, 20.
[0156] In the electroosmotic pump 10A, the pump casing 12 includes
the large-diameter portion 22 and the small-diameter portion 24,
which are arranged in succession from the upstream side. However,
the pump casing 12 is not limited to the above configuration. The
pump casing 12 may have a straight shape as a whole, or may include
a small-diameter portion and a large-diameter portion, which are
arranged in succession from the upstream side.
[0157] An electroosmotic pump 10B according to a second embodiment
shall be described below with reference to FIGS. 3 through 5.
Components of the electroosmotic pump 10B that are identical to
those of the electroosmotic pump 10A according to the first
embodiment shall be denoted by identical reference characters. This
also holds true for other embodiments.
[0158] As shown in FIG. 3, the electroosmotic pump 10B according to
the second embodiment includes a bubble isolator 40 disposed in the
outlet chamber 28, and differs from the electroosmotic pump 10A
according to the first embodiment (see FIGS. 1 and 2) in that the
gas vents 42, 44 and the self-priming mechanism 50 are not provided
therein.
[0159] The electroosmotic pump 10B is used in applications where
the inlet chamber 26 incorporates a countermeasure therein for the
generation of gas and has a large upstream inlet diameter (e.g., 5
mm or greater), and wherein no significant hydrogen gas is produced
in the output chamber 28 when the electroosmotic pump 10B is
operated for a short period of time.
[0160] The bubble isolator 40 disposed in the outlet chamber 28 is
effective to prevent bubbles from flowing into various fluid
devices connected to the downstream side of the fluid passage 14.
Although bubbles accumulate in the outlet chamber 28, this gas will
not largely affect pump operations, insofar as the operating time
of the electroosmotic pump 10B is relatively short and the amount
of produced gas is small. The bubble isolator 40 is also effective
at preventing foreign matter other than bubbles from flowing into
the various fluid devices. Since the electroosmotic pump 10B is
constructed of fewer components, and is capable of preventing
bubbles and foreign matter from flowing downstream, the
electroosmotic pump 10B can be manufactured less costly.
[0161] The electroosmotic pump 10B can be operated reliably by
ensuring that the volume of the outlet chamber 28 is large compared
with the expected amount of the produced gas. The electroosmotic
pump 10B may employ a drive liquid, which is supplied to the fluid
passage 14, wherein the liquid has a low electric conductivity,
thereby producing no significant gas in the vicinity of the
electrodes 18, 20 when a DC voltage is applied to the electrodes
18, 20. The drive liquid may be an alcohol or an organic
solvent.
[0162] As shown in FIG. 4, the electroosmotic pump 10B includes a
large-diameter portion 22 and a small-diameter portion 24, which
are separated from each other and combined in an interfitting
relation to each other, with the bubble isolator 40 being
sandwiched between the large-diameter portion 22 and the
small-diameter portion 24. If a hydrophobic packing, a seat, or an
O-ring, not shown, is inserted between the interfitting region of
the large-diameter portion 22 and the small-diameter portion 24,
then the electrolytic solution can be prevented from leaking out
through the interfitting region.
[0163] As shown in FIG. 5, the electroosmotic pump 10B may include
a large-diameter portion 22 and a small-diameter portion 24, which
are separated from each other and fused or bonded to each other,
with the bubble isolator 40 being fixed to the small-diameter
portion 24.
[0164] In the electroosmotic pump 10B, the pump casing 12 includes
a small-diameter portion 70, a large-diameter portion 22, and a
small-diameter portion 24, which are arranged successively from the
upstream side. However, the pump casing 12 is not limited to the
above configuration.
[0165] An electroosmotic pump 10C according to a third embodiment
shall be described below with reference to FIG. 6.
[0166] The electroosmotic pump 10C according to the third
embodiment differs from the electroosmotic pump 10B according to
the second embodiment (see FIG. 3) in that the large-diameter
portion 22 of the inlet chamber 26 and the small-diameter portion
70 thereof are divided and separated from each other by a bubble
isolator (upstream liquid passing member) 72.
[0167] The bubble isolator 72 is substantially identical in
structure to the bubble isolator 40, and is used in applications
where no significant gas is produced in the vicinity of the inlet
electrode 18, and no significant gas is produced in the vicinity of
the outlet electrode 20, and further wherein the electroosmotic
pump 10C is operated for only a short period of time.
[0168] The electroosmotic pump 10C operates in the same manner and
offers the same advantages as the electroosmotic pump 10B according
to the second embodiment (see FIG. 3). In addition, even if foreign
matter and bubbles flow into the electroosmotic pump 10C from an
upstream side of the fluid passage 14, the bubble isolator 72
prevents such foreign matter and bubbles from flowing into the
inlet chamber 26. As a result, performance of the electroosmotic
pump 10C is maintained.
[0169] An electroosmotic pump 10D according to a fourth embodiment
shall be described below with reference to FIGS. 7 through 14.
[0170] The electroosmotic pump 10D according to the fourth
embodiment differs from the electroosmotic pump 10B according to
the second embodiment (see FIG. 3) in that the gas vent 42 is
disposed in a side wall of the pump casing 12, in the vicinity of
the outlet electrode 20.
[0171] The electroosmotic pump 10D is used in applications where
generation of gas in the inlet chamber 26 causes no significant
problems, and even if gas is produced, the gas bubbles can be
discharged from the inlet chamber 26 by gravity. A reservoir for
supplying the drive liquid to the fluid passage 14 can be connected
to an upstream side of the electroosmotic pump 10D.
[0172] With the electroosmotic pump 10D, even if a large amount of
gas is produced in the vicinity of the electrode 20, the gas can be
discharged through the gas vent 42. Therefore, bubbles are
prevented from being discharged downstream along the fluid passage
14, and the electroosmotic pump 10D can be continuously operated
over a long period of time.
[0173] As shown in FIG. 8, the electroosmotic pump 10D may include
a plurality of holes 74 defined in the side wall of the pump casing
12 around the outlet chamber 28, which are in fluid communication
with the exterior. Further, a gas vent 42 may be disposed on the
pump casing 12 in closing relation to the holes 74.
[0174] As shown in FIGS. 9 and 10, the holes 74 are defined at
equal intervals along the circumferential direction of the pump
casing 12 so as to discharge the gas in the outlet chamber 28
through the holes 74 and the gas vent 42, regardless of the
attitude the electroosmotic pump 10D may be placed in. FIG. 9 shows
four holes 74 defined in a side wall of the pump casing 12 at
90[.degree.] intervals, whereas FIG. 10 shows six holes 74 defined
in the side wall of the pump casing 12 at 60[.degree.]
intervals.
[0175] The gas vent 42 may comprise a plurality of gas vents 42
closing the respective holes 74, or the gas vent 42 may be wound
around the side wall of the pump casing 12 in order to close the
holes 74.
[0176] In FIGS. 7 and 8, the gas vent 42 is made of a hydrophobic
gas-permeable plastic material (e.g., a gas-permeable
heat-shrinkable tube of PTFE). As shown in FIG. 11, the gas vent 42
may also comprise a block of porous ceramics having greater
mechanical strength. The block of porous ceramics is fused or
bonded into the side wall of the pump casing 12 after it has been
made hydrophobic, thereby providing a sufficiently high minimum
water breakthrough point for the drive liquid.
[0177] If the gas vent 42 is not required to be rigid, then the
block of porous ceramics shown in FIG. 11 may be replaced with a
porous sheet or a membrane as shown in FIG. 12. If the sheet or
membrane is disposed in the pump casing 12, then the bonding
strength of the sheet or membrane with respect to the pump casing
12 is maintained.
[0178] As shown in FIGS. 13 and 14, if the bubble isolator 40 is
held in contact with the outlet electrode 20, then a space defined
by the bubble isolator 40, the large-diameter portion 22, and the
electrode 20 serves as a gas vent fluid passage, for discharging
gas generated in the vicinity of the electrode 20 through the gas
vent 42. Therefore, gas can quickly be discharged through the gas
vent 42. Since the outlet electrode 20 and the bubble isolator 40
are held in contact with each other, the drive liquid, which is
discharged from the electroosmotic member 16 through the pores 32,
can directly permeate into the bubble isolator 40 and supplied
therethrough to various fluid devices connected to the downstream
side of the fluid passage 14.
[0179] An electroosmotic pump 10E according to a fifth embodiment
shall be described below with reference to FIG. 15.
[0180] The electroosmotic pump 10E according to the fifth
embodiment differs from the electroosmotic pump 10D according to
the fourth embodiment (see FIG. 7) in that the bubble isolator 72
is disposed in the inlet chamber 26.
[0181] The electroosmotic pump 10E operates in the same manner and
offers the same advantages as the electroosmotic pumps 10C, 10D
according to the third and fourth embodiments (see FIGS. 6 and 7).
The electroosmotic pump 10E may be used in applications where
generation of gas within the inlet chamber 26 causes no problems,
wherein foreign matter and bubbles are prevented by the bubble
isolator 72 from flowing inward from the upstream side of the fluid
passage 14.
[0182] An electroosmotic pump 10F according to a sixth embodiment
shall be described below with reference to FIG. 16.
[0183] The electroosmotic pump 10F according to the sixth
embodiment differs from the electroosmotic pump 10E according to
the fifth embodiment (see FIG. 15) in that the gas vent 44 is
disposed in the side wall of the pump casing 12 in the vicinity of
the inlet chamber 26.
[0184] The electroosmotic pump 10F operates in the same manner and
offers the same advantages as the electroosmotic pumps 10A, 10E
according to the first and fifth embodiments (see FIGS. 1 and 15).
The electroosmotic pump 10F is used in applications where
generation of gas from the inlet electrode 18, as well as
generation of gas from the outlet electrode 20, are significant. If
the pressure in the inlet chamber 26 is higher than the external
pressure around the electroosmotic pump 10E (i.e., the internal
pressure of the electroosmotic pump 10>the external pressure),
then gas can be discharged through the gas vent 44 as a result of
the pressure difference.
[0185] An electroosmotic pump 10G according to a seventh embodiment
shall be described below with reference to FIGS. 17 through 21.
[0186] The electroosmotic pump 10G according to the seventh
embodiment differs from the electroosmotic pump 10F according to
the sixth embodiment (see FIG. 16) in that the self-priming
mechanism 50 is disposed in the inlet chamber 26 instead of the
bubble isolator 72. In the electroosmotic pump 10, the self-priming
mechanism 50 comprises a liquid suction member 52 and an
air-bleeding path 56.
[0187] The electroosmotic pump 10G operates in the same manner and
offers the same advantages as the electroosmotic pumps 10A, 10F
according to the first and sixth embodiments (see FIGS. 1 and 16).
The electroosmotic pump 10G is used in applications where
generation of gas in the vicinity of the inlet electrode 18 as well
as generation of gas in the vicinity of the outlet electrode 20 are
significant, and hence a self-priming function is required for
priming the electroosmotic member 16.
[0188] The liquid suction member 52 having a higher impregnation
pressure and the air-bleeding path 56 having a lower impregnation
pressure are combined with each other so as to control the pressure
in the inlet chamber 26 under these impregnation pressures.
Accordingly, pressurization of the inlet chamber 26 from outside of
the electroosmotic pump 10G is not required, and air within the
inlet chamber 26 as well as gas produced in the vicinity of the
electrode 18 can be discharged efficiently.
[0189] In FIG. 17, the air-bleeding path 56 comprises a simple air
gap. However, as shown in FIG. 18, the air-bleeding path 56 may be
made of a porous material (e.g., glass fibers) having a lower
impregnation pressure than the liquid suction member 52. Since the
impregnation force for the drive liquid in the liquid suction
member 52 is greater than the impregnation force in the
air-bleeding path 56, when the liquid suction member 52 is supplied
with the drive liquid, the liquid quickly permeates the liquid
suction member 52, and then quickly permeates the electroosmotic
member 16 through the pores 30 of the electrode 18. The porous
material may be either hydrophobic or hydrophilic.
[0190] The air-bleeding path 56 may be made of a hydrophobic
gas-permeable material (e.g., a plastic fiber material), rather
than a material having a lower impregnation pressure as shown in
FIG. 18. In this case, when the liquid suction member 52 is filled
with the drive liquid, pressure in the inlet chamber 26 increases,
thereby discharging the air in the inlet chamber 26 through the
air-bleeding path 56.
[0191] As shown in FIGS. 20 and 21, the liquid suction member 52
may be disposed in contact with the inner wall of the
small-diameter portion 70, and may have a plurality of air-bleeding
paths 56 disposed therein along the axial direction of the fluid
passage 14. The air-bleeding paths 56 are made of a hydrophobic
gas-permeable material. If the liquid suction member 52 has dried
inner portions therein when the electroosmotic pump 10G is
reactivated, air within the dried inner portions can be discharged
through the air-bleeding paths 56.
[0192] An electroosmotic pump 10H according to an eighth embodiment
shall be described below with reference to FIGS. 22 and 23.
[0193] The electroosmotic pump 10H according to the eighth
embodiment differs from the electroosmotic pump 10G according to
the seventh embodiment (see FIG. 17) in that the liquid suction
member 52 includes a protrusion 76, which divides and separates the
upstream side of the fluid passage 14 and the inlet chamber 26 from
each other.
[0194] In FIG. 22, the protrusion 76 projects radially outward from
a side wall of the liquid suction member 52, thereby dividing and
separating the large-diameter portion 22 and the small-diameter
portion 70 from each other in the vicinity of the inlet chamber 26.
In FIG. 23, the protrusion 76 projects and abuts against the inner
wall of the small-diameter portion 70.
[0195] The liquid suction member 52 and the protrusion 76 are made
of a hydrophilic material to generate a higher impregnation
pressure with the drive liquid, while also functioning as a bubble
isolator 72 (FIGS. 6 and 15). Stated otherwise, the liquid suction
member 52 and the protrusion 76 function as an upstream liquid
self-priming mechanism, as well as an upstream liquid passing
member. Therefore, the liquid suction member 52 and the protrusion
76 are capable of preventing foreign matter and bubbles from
flowing into the electroosmotic pump 10H, while also preventing air
from flowing upstream from the inlet chamber 26 as a result of
depressurization upstream from the self-priming mechanism 50.
[0196] An electroosmotic pump 10I according to a ninth embodiment
shall be described below with reference to FIG. 24.
[0197] The electroosmotic pump 10I according to the ninth
embodiment differs from the electroosmotic pump 10H according to
the eighth embodiment (see FIGS. 22 and 23) in that a self-priming
mechanism (downstream liquid self-priming mechanism) 80, which is
identical to the self-priming mechanism 50, is disposed in a
downstream region of the fluid passage 14.
[0198] The self-priming mechanism 80 includes a liquid suction
member 82 held in contact with the outlet electrode 20. The liquid
suction member 82 includes a protrusion 84 projecting from a side
wall thereof and defining an outlet chamber 28. As with the liquid
suction member 52, the liquid suction member 82 is made of a
hydrophilic material to generate a high impregnation pressure with
the drive liquid. The protrusion 84 also functions as a bubble
isolator 40 (see FIGS. 1, 3, 6, 7, 15 through 17, 22, and 23).
Stated otherwise, the liquid suction member 82 and the protrusion
84 function as a downstream liquid self-priming mechanism as well
as a downstream liquid passing member. Therefore, the liquid
suction member 82 and the protrusion 84 are capable of preventing
foreign matter and bubbles from flowing downstream along the fluid
passage 14. Gas in the inlet chamber 26 is discharged through the
gas vent 44, and gas in the outlet chamber 26 is discharged through
the gas vent 42. Since the self-priming mechanisms 50, 80 are
disposed respectively in upstream and downstream regions, the drive
liquid can efficiently be discharged from the upstream region
toward the downstream region, and can efficiently be drawn from the
downstream region toward the upstream region. It is preferable for
the liquid suction member 82 to be held in contact with the
electroosmotic member 16, from the standpoint of self-priming the
drive liquid. If the wettability of the outlet electrode 20 with
the electrolytic solution is good, then the electroosmotic member
16 and the liquid suction member 82 can be held in contact with
each other through the outlet electrode 20, i.e., the liquid
suction member 82 and the outlet electrode 20 can be held in
contact with each other. Furthermore, the electroosmotic member 16
and the outlet electrode 20 can also be held in contact with the
liquid suction member 52.
[0199] An electroosmotic pump 10J according to a tenth embodiment
shall be described below with reference to FIG. 25.
[0200] The electroosmotic pump 10J according to the tenth
embodiment differs from the electroosmotic pump 10I according to
the ninth embodiment (see FIG. 24) in that the liquid suction
members 52, 82 do not have the protrusions 76, 84.
[0201] In the electroosmotic pump 10J, the drive liquid can
efficiently be discharged from the upstream region toward the
downstream region, and can efficiently be drawn from the downstream
region toward the upstream region.
[0202] An electroosmotic pump 10K according to an eleventh
embodiment shall be described below with reference to FIG. 26.
[0203] The electroosmotic pump 10K according to the eleventh
embodiment differs from the electroosmotic pump 10D according to
the fourth embodiment (see FIG. 7) in that a liquid suction member
52 is disposed in the inlet chamber 26.
[0204] The electroosmotic pump 10K operates in the same manner, and
offers the same advantages, as the electroosmotic pumps 10D, 10G
according to the fourth and seventh embodiments (see FIGS. 7 and
17), and is capable of discharging gas generated in the vicinity of
the inlet electrode 18 through the air-bleeding path 56. Therefore,
the structure of the pump inlet region is simplified. Specifically,
when conventional pumps are reduced in size, then the reservoir for
the drive liquid also is reduced in size, making it difficult to
fill the electroosmotic member with the drive liquid from outside
of the pump. According to the present embodiment, the liquid
suction member 52, which is effectively permeable to the drive
liquid, is provided, thereby allowing the electroosmotic member to
be filled easily with the drive liquid, so that the reservoir can
be reduced in size.
[0205] An electroosmotic pump 10L according to a twelfth embodiment
shall be described below with reference to FIGS. 27 and 28.
[0206] The electroosmotic pump 10L according to the twelfth
embodiment differs from the electroosmotic pump 10K according to
the eleventh embodiment (see FIG. 26) in that it does not have the
gas vent 42.
[0207] The electroosmotic pump 10L operates in the same manner, and
offers the same advantages, as the electroosmotic pump 10K
according to the eleventh embodiment (see FIG. 26), and may be used
in applications where no gas bleeding is required.
[0208] If the liquid suction member 52 has the protrusion 76, then
the liquid suction member 52 can reliably prevent foreign matter
and bubbles from flowing into the inlet chamber 26, similar to the
electroosmotic pump 10H according to the eighth embodiment (see
FIG. 22).
[0209] An electroosmotic pump 10M according to a thirteenth
embodiment shall be described below with reference to FIGS. 29 and
30.
[0210] The electroosmotic pump 10M according to the thirteenth
embodiment differs from the electroosmotic pump 10L according to
the twelfth embodiment (see FIGS. 27 and 28) in that it does not
include the bubble isolator 40.
[0211] The electroosmotic pump 10M according to the thirteenth
embodiment (see FIG. 29) is used in applications where gas vent is
not required, similar to the electroosmotic pump 10L according to
the twelfth embodiment (see FIGS. 27 and 28). Further, if the
liquid suction member 52 has the protrusion 76 (see FIG. 30), then
the liquid suction member 52 can reliably prevent foreign matter
and bubbles from flowing into the inlet chamber 26, similar to the
electroosmotic pump 10H according to the eighth embodiment (see
FIG. 22).
[0212] An electroosmotic pump 10N according to a fourteenth
embodiment shall be described below with reference to FIGS. 31
through 34.
[0213] The electroosmotic pump 10N according to the fourteenth
embodiment differs from the electroosmotic pump 10M according to
the thirteenth embodiment (see FIGS. 29 and 30) in that a
self-priming mechanism 80 also is disposed in the outlet chamber
28.
[0214] The electroosmotic pump 10N shown in FIG. 31 is used in
applications where gas bleeding is not required, similar to the
electroosmotic pumps 10L and 10M according to the twelfth and
thirteenth embodiments (see FIGS. 27 through 30). Further, if the
liquid suction member 52 has the protrusion 76 (see FIG. 32), then
the liquid suction member 52 can reliably prevent foreign matter
and bubbles from flowing into the inlet chamber 26, similar to the
electroosmotic pump 10H according to the eighth embodiment (see
FIG. 22). Moreover, if the liquid suction member 82 has the
protrusion 84 (see FIG. 33), then the liquid suction member 82 can
reliably prevent foreign matter and bubbles from flowing downstream
along the fluid passage 14, similar to the electroosmotic pump 10H
according to the ninth embodiment (see FIG. 24).
[0215] Even further, if the liquid suction members 52, 82 include
the protrusions 76, 84 (see FIG. 34), then the liquid suction
members 52, 82 can reliably prevent foreign matter and bubbles from
flowing into the inlet chamber 26, while also reliably preventing
bubbles from flowing outward downstream along the fluid passage
14.
[0216] An electroosmotic pump 10O according to a fifteenth
embodiment shall be described below with reference to FIG. 35.
[0217] The electroosmotic pump 10O according to the fifteenth
embodiment has further structural details more specific than those
of the electroosmotic pump 10K according to the eleventh embodiment
(see FIG. 26).
[0218] The pump casing 12 comprises a first portion 12a including
the large-diameter portion 22 and a second portion 12b including
the small-diameter portion 24. The self-priming mechanism 50, the
inlet electrode 18, the electroosmotic member 16, and the outlet
electrode 20 are successively arranged in this order in the first
portion 12a, from the upstream side toward the second portion 12b
thereof. The bubble isolator 40 and the gas vent 42 are disposed in
the second portion 12b, in confronting relation to the
electroosmotic member 16 and the outlet electrode 20. When the
first portion 12a and the second portion 12b are fitted together, a
closed space forming the outlet chamber 28 is defined by the
electroosmotic member 16 and the outlet electrode 20, the bubble
isolator 40 and the gas vent 42, and the first portion 12a and the
second portion 12b.
[0219] A drive liquid absorbing member 86 is disposed between the
liquid suction member 52 of the self-priming mechanism 50 and the
inlet electrode 18 or the electroosmotic member 16. If the liquid
suction member 52 is made of a rigid material, such as a porous
ceramic (e.g., alumina), then the drive liquid absorbing member 86
is provided in order to quickly supply the drive liquid, which has
been introduced into the liquid suction member 52 by way of
self-priming, to the electroosmotic member 16.
[0220] Specifically, the drive liquid absorbing member 86 is made
of a pliable, water-absorbing, hydrophilic and water-retentive
material, such as a hydrophilic spongy porous body (with pore
diameters ranging from 10 [.mu.m] to 100 [.mu.m]), a sheet of paper
pulp, or a sheet of synthetic fibers, wherein the material closely
contacts with the surface of the electroosmotic member 16 and to
the surface of the liquid suction member 52. For example, the drive
liquid absorbing member 86 comprises a hydrophilic sheet having a
thickness of 1 [mm], which is sandwiched and pressed between the
liquid suction member 52 (a porous ceramic with a pore diameter of
about several tens [.mu.m]) and the electroosmotic member 16 (a
porous ceramic with a pore diameter ranging from several tens [nm]
to several [.mu.m]), for increasing contact thereof to the surface
of the liquid suction member 52 and to the surface of the
electroosmotic member 16, such that the liquid suction member 52
and the electroosmotic member 16 are reliably joined to each other
through the drive liquid absorbing member 86.
[0221] Therefore, the drive liquid, which has been introduced by
the liquid suction member 52 by way of self-priming, can quickly be
supplied to the electroosmotic member 16, thereby improving pump
performance.
[0222] Furthermore, since the drive liquid absorbing member 86 also
functions as a cushion between the liquid suction member 52 and the
electroosmotic member 16 or the inlet electrode 18, these
components can be assembled efficiently.
[0223] If the wettability of the inlet electrode 18 with respect to
the drive liquid is good, then the drive liquid absorbing member 86
can be made of a material which closely contacts with the inlet
electrode 18, whereby the electroosmotic member 16 and the drive
liquid absorbing member 86 are held in contact with the inlet
electrode 18 interposed therebetween, i.e., the drive liquid
absorbing member 86 and the inlet electrode 18 are held in contact
such that the drive liquid absorbing member 86 is sandwiched
between the inlet electrode 18 and the liquid suction member 52. In
this case, the electroosmotic member 16 can be supplied with the
drive liquid from the liquid suction member 52 as well as through
the drive liquid absorbing member 86.
[0224] Furthermore, the drive liquid absorbing member 86 can be
made of a material which closely contacts with the inlet electrode
18 and the liquid suction member 52, wherein the electroosmotic
member 16 and the inlet electrode 18 are held in contact with the
drive liquid absorbing member 86 with the inlet electrode 18 being
interposed therebetween, i.e., the drive liquid absorbing member 86
can be held in contact with the electroosmotic member 16 and the
inlet electrode 18, wherein the drive liquid absorbing member 86 is
sandwiched between the electroosmotic member 16 and/or the inlet
electrode 18 and the liquid suction member 52. In this case, the
electroosmotic member 16 can be supplied with the drive liquid from
the liquid suction member 52 through the drive liquid absorbing
member 86.
[0225] If the inlet electrode 18 is made of a material whose
wettability with respect to the drive liquid is not good, such as
platinum-supported carbon, carbon fibers, stainless steel mesh, or
the like, then it is desirable that the diameter of the pores 30 of
the inlet electrode 18 be increased, and the electroosmotic member
16 and the drive liquid absorbing member 86 be held in direct
contact with each other through the pores 30.
[0226] The second portion 12b includes a surface, which faces the
outlet electrode 20, and which includes a central region where the
fluid passage 14 is defined. The central region is provided as a
convex region 90 projecting toward the outlet electrode 20, wherein
the bubble isolator 40 is mounted on the convex region 90. The
surface of the second portion 12b, which faces the outlet electrode
20, also includes a concave region 88 therein adjacent to the
convex region 90, wherein the gas vent 42 is disposed in the
concave region 88. The second portion 12b includes a plurality of
holes 74 defined therein, which extend from the gas vent 42
downstream (on the left in FIG. 35) with respect to the direction
in which the drive liquid flows.
[0227] In FIG. 35, the surface of the second portion 12b, which
faces the outlet electrode 20, and which was originally a flat
surface, is partially processed into the concave region 88, with a
central region thereof being formed as the convex region 90.
However, an area around the region of the bubble isolator 40 may be
formed as the concave region 88, wherein the gas vent 42 is
disposed in the concave region 88. Stated otherwise, at least the
central region on which the bubble isolator 40 is disposed
preferably should not be processed into the concave region 88.
[0228] If the bubble isolator 40 comprises a hydrophilic
polyethersulfone membrane (having pores with a diameter of 0.2
[.mu.m]), then a minimum bubble point of about 300 [kPa] is
obtained. In this case, the bubble isolator 40 is bonded to the
convex region 90, so as to provide a shield between the outlet
chamber 28 and the portion of the fluid passage 14 within the
small-diameter portion 24 (i.e., the downstream side of the fluid
passage 14).
[0229] If the gas vent 42 comprises a PTFE porous membrane (having
pores with a diameter of 0.1 [.mu.m]), then a minimum water
breakthrough point of 300 [kPa] or higher is obtained. In this
case, the gas vent 42 is bonded to the concave region 88 in order
to provide a shield between the outlet chamber 28 and the holes
74.
[0230] The bubble isolator 40 may be bonded to the convex region
90, and the gas vent 42 may be bonded to the concave region 88, by
means of ultrasonic fusion, thermal fusion, adhesive bonding, laser
beam welding, or the like.
[0231] The holes 74 are of a size that allows gas to be discharged
from the outlet chamber 28 through the gas vent 42 at a
predetermined rate. The holes 74 should preferably be of a circular
shape or in the form of slits (e.g., having a hole diameter ranging
from 0.1 [mm] to 2 [mm]) so that the tensile load applied to the
PTFE membrane (the gas vent 42) under pressure in the outlet
chamber 28 is not excessive. The edges of the holes 74 which are
held against the PTFE membrane (i.e., the upstream edges of the
holes 74) should preferably be beveled to prevent the PTFE membrane
from being damaged.
[0232] The gap provided by the outlet chamber 28 along the
direction of the fluid passage 14, i.e., the gap (interval) between
the electroosmotic member 16 or the outlet electrode 20 and the gas
vent 42, as well as the gap (interval) between the electroosmotic
member 16 or the outlet electrode 20 and the bubble isolator 40,
are important parameters affecting characteristics of the
electroosmotic pump 10O. Such gaps should preferably be within a
range of from 1 [.mu.m] to 3 [mm]. Specifically, the gap when
surface tension is more dominant than gravitation should be about 3
[mm], whereas the gap when resistance posed by the fluid passage 14
is very large should be less than 1 [.mu.m]. Therefore, in terms of
the characteristics of the electroosmotic pump 10O, it is
preferable for each of the gaps to be set at appropriate values
(e.g., about 1 [mm]) within a range from an upper value of 3 [mm]
to a lower value of 1 [.mu.m].
[0233] By setting the above gaps to a certain small value in the
above range, the bubbles produced in the electroosmotic pump 10O
can be limited to a certain size. Therefore, the pump operation is
stabilized, and fluctuations of the pump flow rate are reduced when
the gas is discharged from the outlet chamber 28 through the gas
vent 42 and the holes 74. Furthermore, the dead volume of the
electroosmotic pump 10O can be reduced. Moreover, since the effect
that the gravitational force has on the discharging of gas is
reduced by setting the gaps to a size in the above range, the pump
characteristics remain unchanged no matter what direction the
electroosmotic pump 10O may be oriented, with the result that the
electroosmotic pump 10O is orientation-free. For example, the
downstream side (the small-diameter portion 24) of the
electroosmotic pump 10O may be oriented upwardly.
[0234] If bubbles are present in the outlet chamber 28, flow of the
drive liquid within the fluid passage 14 may be stopped, or the
flow rate of the drive liquid may be varied. However, the gas vent
42 disposed in the concave region 88 is effective to discharge
bubbles, which are more likely to remain within the concave region
88 than on the convex region 90, efficiently from the gas vent 42
and through the holes 74. More specifically, since bubbles cannot
pass through the bubble isolator 40 provided on the convex region
90, the bubbles move into the concave region 88 disposed alongside
the convex region 90, and are discharged from the gas vent 42
through the holes 74, due to the internal pressure in the outlet
chamber 28.
[0235] With the electroosmotic pump 10O according to the fifteenth
embodiment, therefore, drive liquid, which has been introduced into
the liquid suction member 52 by way of self-priming, is efficiently
absorbed by the drive liquid absorbing member 86, and is quickly
supplied to the electroosmotic member 16. When the DC power supply
34 applies a DC voltage to the inlet electrode 18 and the outlet
electrode 20, the drive liquid in the electroosmotic member 16 is
supplied from the outlet chamber 28, through the bubble isolator
40, and outside of the electroosmotic pump 10O. Bubbles in the
outlet chamber 28 are discharged from the gas vent 42 through the
holes 74.
[0236] With respect to the electroosmotic pump 10O according to the
fifteenth embodiment, it has been described that the drive liquid
absorbing member 86 is sandwiched between the liquid suction member
52 and the electroosmotic member 16 and/or the first electrode 18
upstream from the electroosmotic member 16, or between the liquid
suction member 52 and the first electrode 18, in the fluid passage
14. However, instead of this arrangement (or in addition to this
arrangement), the drive liquid absorbing member 86 may be
sandwiched between the liquid suction member 82 (see FIGS. 24, 25,
and 31 through 34) and the electroosmotic member 16 and/or the
second electrode 20 downstream from the electroosmotic member 16,
or between the liquid suction member 82 and the second electrode
20, thus obtaining the same advantages as described above.
[0237] With respect to the electroosmotic pump 10O according to the
fifteenth embodiment, it has been described that the gap between
the electroosmotic member 16 or the outlet electrode 20 and the gas
vent 42, as well as the gap between the electroosmotic member 16 or
the outlet electrode 20 and the bubble isolator 40, are in a range
of from 1 [.mu.m] to 3 [mm] along the direction of the fluid
passage 14. However, instead of this arrangement (or in addition to
this arrangement), the gap between the electroosmotic member 16 or
the inlet electrode 18 and the gas vent 44 (see FIGS. 1, 16, 17,
and 22 through 25), as well as the gap between the electroosmotic
member 16 or the inlet electrode 18 and the bubble isolator 72 (see
FIGS. 6, 15, and 16), may be within a range of from 1 [.mu.m] to 3
[mm], thus obtaining the same advantages as described above.
[0238] An electroosmotic pump 10P according to a sixteenth
embodiment shall be described below with reference to FIG. 36.
[0239] The electroosmotic pump 10P according to the sixteenth
embodiment differs from the electroosmotic pumps 10A through 10O
according to the first through fifteenth embodiments (see FIGS. 1
through 35) in that both an upstream end (inlet 87) and a
downstream end (outlet 89) of the fluid passage 14 are defined in a
surface 91 (on the right in FIG. 36), whereas a gas vent 42 and
holes 74 are defined in an opposite surface 93 (on the left in FIG.
36).
[0240] The electroosmotic pump lop according to the sixteenth
embodiment can be installed on (connected to) an installation
surface such as a board or the like with enhanced ease, and can be
reduced in overall height. Therefore, the electroosmotic pump 10P
is suitable for use as a small-size surface-mounted pump in
electronic devices, for example.
[0241] A liquid feeding device 110 incorporating the electroosmotic
pump 10O according to the fifteenth embodiment (see FIG. 35) shall
be described below with reference to FIG. 37.
[0242] The liquid feeding device 110 includes a tubular liquid
container 92 (e.g., having a depth of 15 [cm]) having a closed
bottom and an open top, wherein the liquid container 92 is filled
with a liquid fuel 94 such as methanol or methanol water diluted
with water. The electroosmotic pump 10O is mounted on top of the
liquid container 92, with the downstream side (the small-diameter
portion 24) thereof being oriented upwardly. The liquid container
92 houses a liquid fuel absorbing member 96 therein, which is
capable of effectively absorbing the liquid fuel 94 and is coupled
to the liquid suction member 52.
[0243] The liquid fuel absorbing member 96 should preferably be
made of a hydrophilic porous material having a large porosity, or a
fibrous material (e.g., a water-retentive material of natural pulp
fibers). However, the liquid fuel absorbing member 96 may be made
of the same material as the liquid suction member 52, or
preferably, may be made of a material having a larger water
retaining capability than the material that forms the liquid
suction member 52.
[0244] The liquid fuel 94 absorbed in the liquid fuel absorbing
member 96 is introduced by way of self-priming into the liquid
suction member 52 through the liquid fuel absorbing member 96. Then
the liquid fuel 94 is supplied to the electroosmotic member 16
through the drive liquid absorbing member 86. When the DC power
supply 34 applies a DC voltage to the inlet electrode 18 and the
outlet electrode 20, the liquid fuel 94 in the electroosmotic
member 16 is supplied from the outlet chamber 28, through the
bubble isolator 40, and outside of the electroosmotic pump 10O,
while the bubbles in the outlet chamber 28 are discharged from the
gas vent 42 through the holes 74.
[0245] A liquid fuel 94, such as methanol or methanol water, is
used as the fuel for a fuel cell system. Therefore, the liquid fuel
94 in the liquid container 92 can be supplied to the fuel cell
system via a simple structure.
[0246] If the liquid fuel 94 comprises 100 [%] methanol, then even
if bubbles are produced in the electroosmotic pump 10O when the
liquid fuel 94 is supplied thereto, all of the bubbles are
dissolved in the methanol because solubility of the bubbles in
methanol is large. Therefore, the above gas vent structure (the gas
vents 42 and the holes 74) may be dispensed with. If the liquid
fuel 94 comprises methanol water, then since the presence of water
increases the pump current and the solubility of the gas is small,
generation of bubbles cannot be avoided. However, since the
electroosmotic pump 10O has a gas vent structure made up of the gas
vents 42 and the holes 74, the produced bubbles can efficiently be
discharged from the electroosmotic pump 10O.
[0247] Inasmuch as the electroosmotic pump 10O is an
orientation-free pump, it can be supplied with liquid fuel 94 no
matter what attitude the electroosmotic pump 10O is placed in.
Thus, the electroosmotic pump 10O is suitable for use in a mobile
device or the like. Since the liquid fuel absorbing member 96 is
disposed in the liquid container 92, the liquid fuel 94 stored
inside the liquid container 92 can be supplied out of the liquid
container 92 in its entirety.
[0248] If the electroosmotic pump 10O and the liquid fuel absorbing
member 96 are removably mounted in the liquid container 92, then
the electroosmotic pump 10O and the liquid fuel absorbing member 96
may be combined with a fuel cell system, wherein only the liquid
container 92 is replaced to enable the liquid fuel 94 to be
replenished easily.
[0249] The electroosmotic pump 10O according to the fifteenth
embodiment (see FIG. 35) has been described above as being
incorporated in the liquid feeding device 110. However, the
electroosmotic pumps 10A through 10N and 10P according to the first
through fourteenth and sixteenth embodiments (see FIGS. 1 through
34 and 36) may also be used to supply the liquid fuel 94 out of the
liquid container 92.
[0250] The electroosmotic pumps and the liquid feeding devices
according to the present invention are not limited to the above
embodiments, but various other arrangements may be employed without
departing from the gist of the present invention.
INDUSTRIAL APPLICABILITY
[0251] With the electroosmotic pump according to the present
invention, even when gas is produced in the vicinity of the second
electrode as a result of application of voltage, the downstream
liquid passing member, which is disposed downstream from the
electroosmotic member, passes the drive liquid while preventing gas
from passing therethrough. Therefore, gas is prevented from flowing
into any of various fluid devices, such as a microfluid chip or the
like, connected downstream from the electroosmotic member. Further,
the electroosmotic pump can accurately control the position of the
liquid that passes through the fluid device.
[0252] Furthermore, with the electroosmotic pump according to the
present invention, since the upstream liquid self-priming mechanism
and the electroosmotic member are held in contact with each other,
when the upstream liquid self-priming mechanism is filled with
drive liquid from outside, the drive liquid quickly permeates the
electroosmotic member from the upstream liquid self-priming
mechanism. When voltage is then applied to the electrodes, it is
possible to reliably discharge the drive liquid from the
electroosmotic member to the downstream side of the fluid passage.
As a result, the self-priming capability of the electroosmotic pump
is maintained, even if there is gas present in the vicinity of the
first electrode.
[0253] With the electroosmotic pump according to the present
invention, moreover, when voltage is applied to the first and
second electrodes of the electroosmotic pump, the liquid stored in
the liquid casing is supplied to the outside from the
electroosmotic pump. Therefore, liquid can be supplied by means of
a simple structure.
* * * * *