U.S. patent application number 15/121492 was filed with the patent office on 2016-12-22 for all-liquid electrorheological effect.
The applicant listed for this patent is THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY. Invention is credited to Shuyu CHEN, Xiaolin LI, Ping SHENG, Weijia WEN, Bing ZHANG.
Application Number | 20160369202 15/121492 |
Document ID | / |
Family ID | 54239398 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160369202 |
Kind Code |
A1 |
SHENG; Ping ; et
al. |
December 22, 2016 |
ALL-LIQUID ELECTRORHEOLOGICAL EFFECT
Abstract
An apparatus for generating a giant electrorheological (ER)
effect includes an upper high voltage electrode and a lower high
voltage electrode, the upper high voltage electrode and the lower
high voltage electrode each covered with a water-absorbing material
and have water absorbed thereon. The apparatus also includes a
fluid channel formed by layers and positioned in a gap between the
upper high voltage electrode and the lower high voltage electrode;
a pressure sensor positioned at one of the high voltage electrodes;
a pump to flow silicon oil through the fluid channel; and a high
voltage source configured to apply a voltage to the upper high
voltage electrode. A method for generating a ER utilizes the
apparatus.
Inventors: |
SHENG; Ping; (Hong Kong,
CN) ; ZHANG; Bing; (Hong Kong, CN) ; LI;
Xiaolin; (Hong Kong, CN) ; CHEN; Shuyu; (Hong
Kong, CN) ; WEN; Weijia; (Hong Kong, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY |
Kowloon, Hong Kong |
|
CN |
|
|
Family ID: |
54239398 |
Appl. No.: |
15/121492 |
Filed: |
March 31, 2015 |
PCT Filed: |
March 31, 2015 |
PCT NO: |
PCT/CN2015/075497 |
371 Date: |
August 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61967969 |
Mar 31, 2014 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10M 173/02 20130101;
F16D 2037/001 20130101; C10M 2201/02 20130101; C10M 171/001
20130101; C10N 2070/00 20130101; C10M 2229/025 20130101; C10M
2227/003 20130101 |
International
Class: |
C10M 171/00 20060101
C10M171/00; C10M 173/02 20060101 C10M173/02 |
Claims
1. An apparatus for generating an electrorheological (ER) effect
comprising: an upper voltage electrode and a lower voltage
electrode, the upper voltage electrode and the lower voltage
electrode each covered with a water-absorbing material and have
water absorbed thereon; a fluid channel formed by layers and
positioned in a gap between the upper voltage electrode and the
lower voltage electrode; a pressure sensor positioned at one of the
voltage electrodes; a pump to flow silicon oil through the fluid
channel; and a voltage source configured to apply a voltage to the
upper voltage electrode.
2. The apparatus according to claim 1, wherein the gap between the
upper voltage electrode and the lower voltage electrode is selected
from 1 mm, 0.75 mm and 0.5 mm.
3. The apparatus according to claim 1, wherein the pump is a
syringe pump.
4. The apparatus according to claim 1, wherein the water absorbing
material is a polyester-based water absorbing membrane.
5. The apparatus according to claim 1, wherein the voltage applied
to the electrodes is between 1 kV and 6 kV, inclusive.
6. The apparatus according to claim 1, further comprising a
function generator configured to send a control signal to the
voltage source.
7. The apparatus according to claim 6, wherein the control signal
is rectangular wave, duration of the signal is 40 seconds, and duty
cycle is 0.5.
8. A method for generating an electrorheological (ER) effect
comprising: providing an apparatus, the apparatus comprising: an
upper voltage electrode and a lower voltage electrode, the upper
voltage electrode and the lower voltage electrode each covered with
a water-absorbing material and have water absorbed thereon; a fluid
channel formed by layers and positioned in a gap between the upper
voltage electrode and the lower voltage electrode; a pressure
sensor positioned at one of the voltage electrodes; a pump; and a
voltage source configured to apply a voltage to the upper voltage
electrode and the lower voltage electrode; flowing silicone oil
through the fluid channel using the pump; and applying voltage to
the upper voltage electrode, thereby creating an electric field and
generating the ER effect.
9. The method according to claim 8, wherein the gap between the
upper voltage electrode and the lower voltage electrode is selected
from 1 mm, 0.75 mm and 0.5 mm.
10. The method according to claim 8, wherein the pump is a syringe
pump.
11. The method according to claim 8, wherein the water absorbing
material is a polyester-based water absorbing membrane.
12. The method according to claim 8, wherein the voltage applied to
the electrodes is between 1 kV and 6 kV, inclusive.
13. The method according to claim 8, further comprising a function
generator configured to send a control signal to the voltage
source.
14. The method according to claim 8, wherein the control signal is
rectangular wave, duration of the signal is 40 seconds, and duty
cycle is 0.5.
15. An all-liquid electrorheological (ER) fluid comprising: a
mixture of about 85-95 wt % silicon oil and about 5-15 wt % water,
wherein the silicon oil and water are uniformly mixed; and the
mixture exhibits electrorheological effects when an outside voltage
is applied to the mixture.
16. The all-liquid ER fluid of claim 15, wherein the amount of
silicon oil present is 90 wt % and the amount of water present is
90 wt %.
Description
BACKGROUND
[0001] Electric dipole, i.e. a positive charge and a negative
charge separated by small distance, is probably the most common
form of electrical entity in the world. Electric dipole moment is
the measure of the separation of the positive and negative charges
in a system or a measure of the charge system's overall polarity.
Molecules with permanent molecular dipoles are denoted as polar
molecules. For example, water molecules have a dipole moment of 2.7
D and urea molecules have a larger dipole moment of 4.6 D.
[0002] Molecular dipoles are typically randomly orientated or
oppositely paired with the result that no net long range electric
field is produced. However, molecular dipoles can be made to
perform differently, and research into the ordering structures and
thermodynamic properties of water molecules in the presence of
different nano-confinements is varied and extensive. For example,
molecular filaments have been observed in water-carbon nanotube
(CNT) systems, and bilayer ice has been formed at 300K when water
molecules are confined between nanoscale hydrophobic plates.
Likewise, external application of an electric field can drive polar
(hydrophilic) molecules into the non-polar (hydrophobic) phase. Due
to the confinement exerted by the non-polar phase, the invading
polar molecules tend to form some ordered structures, leading to a
dramatic change in the rheological properties of the system.
[0003] Molecular dipoles can be made to align at contact regions of
purpose fabricated nanoparticles under a moderate electric field,
which results in large adhesion forces between the nanoparticles.
This phenomenon, e.g. molecular dipole filament formation, was
identified as the microscopic mechanism of, and is generally known
as, the giant electrorheological (GER) effect. GER effect has been
demonstrated in the formation of aligned molecular dipole filaments
under the confinement effect of silicone oil chains.
In the context of the GER effect, urea molecules can penetrate a
silicone oil layer with a thickness of several nanometers to form
filament structures. However, the large energy barrier .sigma. that
must be overcome, results in urea filaments of a limited length.
Urea coated BaTi(C.sub.2O.sub.4).sub.2 nanoparticles in silicone
oil suspension exhibit a GER effect with the yield stress one order
of magnitude larger than that of traditional ER fluids. Moreover,
yield stress of GER fluids depends linearly on the electric field,
which is quite different from the quadratic dependence shown by the
ER fluids of the present disclosure and the tradition ER fluids.
These characteristic yield stresses are accounted for by the urea
dipole filaments formed in the contact region between two
neighboring nanoparticles. Molecular dynamic (MD) simulation
reveals that under the application of the electric field, urea
molecular filaments are formed by penetrating the silicone oil
layer from two sides, with the molecular dipoles predominantly
aligned along the direction of the applied field. This ordered
structure maximizes the number of hydrogen bonds formed between the
invading urea molecules and minimizes the dipole field interaction
energy to overcome the unfavorable energy barrier .sigma.. The
confinement effect on the urea filaments is offered by the silicone
oil chains through the repulsive interaction between the silicone
oil methyl groups and certain atoms in the urea molecules. Two
sides of the gap are bridged by the filaments and a large
attractive interaction arises leading to the GER effect. MD
simulations using various gap sizes were conducted to determine the
possibility of finding a urea molecule at the center of the gaps
with different gap sizes. At 9 nm the possibility decreased to
nearly zero. Thus, a physical, molecular bridge should be observed
only at a smaller gap size. BRIEF
SUMMARY
[0004] The instant subject matter is directed to an apparatus for
generating an electrorheological (ER) effect comprising an upper
voltage electrode and a lower voltage electrode, the upper voltage
electrode and the lower voltage electrode each covered with a
water-absorbing material and have water absorbed thereon; a fluid
channel formed by layers and positioned in a gap between the upper
voltage electrode and the lower voltage electrode; a pressure
sensor positioned at one of the voltage electrodes; a pump to flow
silicon oil through the fluid channel; and a voltage source
configured to apply a voltage to the upper high voltage
electrode.
[0005] In another embodiment, the instant subject matter is direct
to methods for generating an electrorheological (ER) effect
comprising: providing an apparatus, the apparatus comprising: an
upper voltage electrode and a lower voltage electrode, the upper
voltage electrode and the lower voltage electrode each covered with
a water-absorbing material and have water absorbed thereon; a fluid
channel formed by layers and positioned in a gap between the upper
voltage electrode and the lower voltage electrode; a pressure
sensor positioned at one of the voltage electrodes; a pump; and a
voltage source configured to apply a voltage to the upper voltage
electrode and the lower voltage electrode; flowing silicone oil
through the fluid channel using the pump; and applying voltage to
the upper voltage electrode, thereby creating an electric field and
generating the ER effect.
[0006] In yet another embodiment, the instant subject matter is
directed to an all-liquid electrorheological (ER) fluid comprising:
a mixture of about 85-95 wt % silicon oil and about 5-15 wt %
water, wherein the silicon oil and water are uniformly mixed; and
the mixture exhibits electrorheological effects when an outside
voltage is applied to the mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 depicts a photograph of finished sample including
high voltage electrodes and a fluid channel.
[0008] FIG. 2 depicts the structure of polymethylmethacrylate
(PMMA) layers for laser engraving.
[0009] FIG. 3 illustrates an experiment setup system.
[0010] FIG. 4 depicts the pressure measurement before the
application of high voltage.
[0011] FIG. 5 depicts the pressure measurement after the
application of high voltage.
[0012] FIG. 6 depicts the introduction of an effective surface
charge density.
[0013] FIG. 7 depicts the measured increment in pressure difference
of water-silicone oil systems with a 0.5 mm gap.
[0014] FIG. 8 depicts the measured increment in pressure difference
of water-silicone oil systems with a 0.75 mm gap.
[0015] FIG. 9 depicts the measured increment in pressure difference
of water-silicone oil systems with a 1 mm gap
[0016] FIG. 10 depicts the measured increment in pressure
difference of water-decane system with a 1 mm gap.
[0017] FIG. 11 depicts the measured .DELTA.P'' as a function of the
voltage applied with the quadratic fittings represented by the
solid line.
[0018] FIG. 12 depicts the pressure difference plotted as the
function of E.sup.2.
[0019] FIG. 13 illustrates the experimental setup used for
measuring GER effect.
[0020] FIG. 14 depicts the measured shear stress as a function of
time (red curve), with the voltage pattern (black curve) plotted on
the same graph.
[0021] FIG. 15 depicts the theoretical relationship between yield
stress and strain.
[0022] FIG. 16 depicts a MD snapshot showing the initial
configuration of the simulation in Example 8.
[0023] FIG. 17 MD snapshot showing the giant water molecular
filaments with the presence of the electric field.
[0024] FIG. 18 depicts a sample of 5 .mu.m gap was made of two
water-penetrable AAO membranes sandwiched by two metal mesh
electrodes.
[0025] FIG. 19 depicts the schematic structure of sample with gap
size .about.5 .mu.m.
[0026] FIG. 20 Measured .DELTA.P'' as a function of the voltage
applied for small gap size (5.15 .mu.m) sample.
DETAILED DESCRIPTION
[0027] In the context of the instant subject matter, it has been
found that the above shortcomings of known filament formation
systems, namely finite filament length, can be overcome. For
example, water can form macroscopic molecular filaments or files in
silicone oil phase under an externally applied electric field. To
this end, a microfluidic method for measuring the
electrorheological (ER) effect originated from the field induced
dipolar filament formation has been developed. The broad model
includes a flow channel, two parallel plate electrodes coated with
water-absorbing material(s), a syringe pump, a pressure sensor, and
a high voltage source, e.g. electrodes. The amount of absorbed
water on the electrodes and the volume rate of the carrier flow
through the channel are carefully controlled, while the pressure
difference across the channel is monitored. This method is more
sensitive, accurate, and reliable than the known rotational ER
meter, thereby expanding new possibilities in new material design
and industrial applications.
[0028] Furthermore, recognition of molecular dipole filament
formation as the microscopic mechanism of the giant
electrorheological (GER) effect implies the possibility of the
formation of macroscopic molecular dipole filaments inside a
hydrophobic phase along the direction of the externally applied
electric field. The electrorheological (ER) effect resulting from
such structures can be defined as the molecular ER effect, which
has been recently realized experimentally in water-silicone oil
systems by using the microfluidic method.
[0029] The energy barrier for one urea molecule penetrating into
silicone oil as a molecular filament can be larger than k.sub.BT
(k.sub.B represents the Boltzmann Constant and T represents
temperature). However, the dipole field interaction can only
compensate for one k.sub.BT per polar molecule, as the magnitude of
the field goes to infinity. From Boltzmann statistics, it is
possible to calculate the average fluctuating filament length
N.sub..sigma. by
N .sigma. = 1 / ( exp ( .sigma. - .DELTA. p E k B T ) - 1 ) , ( 1 )
##EQU00001##
where T denotes room temperature, N is the number of urea molecules
in the filament, .DELTA.p is the difference of the dipole moment
per molecule along the field direction between the filament state
and bulk states, and E is the electric free energy in the field.
The filaments are formed between the two substrates when the
separation distances are on the order of 2N.sub.94 l or slightly
larger. l denotes the size of the dipolar molecules. Since
-.DELTA.p .fwdarw.-k.sub.BT is the limit of |E|.fwdarw..infin.,
and, in the case of urea/silicone oil, a .sigma.>k.sub.BT,
determines the maximum saturation gap/saturation behavior of urea
filaments. In relation to Equation (1), the critical investigation
is whether any type of dipolar molecules exist having a
.sigma..about.k.sub.BT or even a .sigma.<k.sub.BT so that the
critical electric field at which .sigma.-.DELTA.p =0 exists can be
employed to produce macroscopic length filaments of these
particular dipolar molecules.
[0030] Accordingly, a microfluidic method for measuring the
electrorheological effect originating from the field induced
dipolar filament formation that can be further defined as molecular
ER effect is demonstrated using a channel between two parallel
plate electrodes coated with water absorbing layers of material. In
the model of the present subject matter, the volume rate of the
carrier flow through the channel can be precisely controlled by a
pump, in particular a syringe pump. However, other pumping
mechanisms are also contemplated within the present apparatus and
method. The pressure difference across the channel is monitored by
a high sensitivity pressure sensor. An increment in the monitored
pressure difference .DELTA.P'' can be recorded if the field-induced
molecular dipole filaments are formed. For water molecules, it is
possible to form giant molecular filaments across gaps as large as
.about.1 mm (macromolecular) in silicone oil phase. .DELTA.P''
demonstrated quadratic dependence on the applied electric field in
the presence of sufficient water supply. However, this gradually
shifted to a linear dependency on the applied electrical field as
the water supply was exhausted.
[0031] Using the apparatus and method of the present subject
matter, the largest pressure increment measured at .about.5 kV/mm
was 120 Pa. Interestingly, it is noted that this effect disappears
when silicone oil is substituted by decane. Also, quadratic field
dependence implies .DELTA.P'' can reach the order of MPa when the
gap size decreases to several microns. This is in sharp contrast to
the linear effects observed when using urea molecules in silicon
oil at distances of only a few nanometers.
[0032] Quadratic field dependence can also be modeled
theoretically, thus verifying that the yield stress can reach the
order of MPa when the gap size decreases to several microns. This
corresponds to an electric energy density higher than that of any
prior art GER materials. The method can be applied in may
microfluidic-based devices, such as micro-clutches, micro-valves
and micro-dampers, and facilitate the control of the fluidic logic
systems. The mechanism can be applied to design functional
materials, such as new GER materials, and biomaterials.
EXAMPLES
Example 1
Fabrication of Microfluidic Measurement Apparatus
[0033] The apparatus is made of two major features: a pair of
electrodes coated with water absorbing material(s) and a fluid
channel (FIG. 1.). Voltage is applied directly on the electrodes
and fluid flows through the channel between the electrodes. The
pressure sensor is put near the electrodes to measure the pressure
difference. Polymethylmethacrylate (PMMA) film is used as the walls
of channel. The upper electrode is inserted into the PMMA wall. The
lower electrode is made of a copper film and bonded with a spacer.
The spacer is also made of PMMA film and the gap size (electrodes
distance) is determined by the thickness of the spacer. In one
aspect, the gap size is selected from 1 mm, 0.75 mm or 0.5 mm. It
is noted that these gap sizes are much larger than the nanometer
gaps found in the prior art systems.
[0034] PMMA 2-mm film was fabricated by the laser engraving machine
(Universal Laser System) to form an electrode groove (FIG. 2). The
six 3-mm diameter holes near the boundary facilitate mechanical
sealing. The rectangular part (28 mm.times.10 mm) in layer 1 was
cut away. The corresponding area in layer 2 was engraved to a depth
around 200 .mu.m. The square part in layer 2, the two 1 mm diameter
small holes near the groove, and the bigger hole on the right of
the groove were also cut through. The PMMA film in layer 3 served
as the spacer to be put in the middle of the electrodes and control
the channel height (0.5 mm, 0.75 mm or 1 mm). Layer 1 and layer 2
were bonded together with an acrylic solvent, with the gaps sealed,
including the six holes for the screws and two small holes.
[0035] A 2 mm thick copper block (28 mm.times.10 mm) was machined,
and another part of the electrode was made of copper film at a 1 mm
thickness. The film corresponded in size to layer 3 (FIG. 2). Six
holes were machined into the block to facilitate mechanical
sealing. The PMMA spacer was attached to the copper film with 502
strong adhesive with pre-alignment. The copper block was inserted
into the groove formed by layer 1 and layer 2 (FIG. 2) and affixed
with epoxy.
[0036] Wire was connected to the electrodes through a square groove
of the copper block and on the copper sides of the spacer layer
part using tin solder, after the electrodes and the PMMA were
bonded. The epoxy was then covered on the tin solder joint to fix
the wire. A 0.9 mm stainless steel tube was inserted into the two
small holes in the bonded PMMA as an inlet and connector for a
pressure sensor. Plasticene was used to block the hole on the inner
side. Epoxy was covered near the tube for sealing. Plastic hose was
used to be the outlet. The finished upper and lower electrodes were
combined thereby forming a fluid channel. Polydimethylsiloxane
(PDMS) thin film was applied as a mechanical sealant. The PDMS thin
film was fabricated with spin coater with a thickness of .about.50
.mu.m.
Example 2
Measurement Protocol
[0037] The measurement experiment protocol requires the above
measurement apparatus of Example 1, syringe pump, pressure sensor,
multimeter, high voltage source, function generator and computer
interface (FIG. 3). Polyester-based water-absorbing membrane
(MEMBRA-CEL MC18.times.100 CLR) was immersed into deionized water
for around 10 min. Then the membrane was cut and attached on the
electrodes. A Philips PM5134 function generator triggered the DC
high voltage supply with different generated signal (using a
SPELLMAN SL300) which was connected with the upper electrode. High
voltage signal was rectangular wave; duration was 40 s; and the
duty cycle was 0.5. The signal was applied until breakdown
occurred. The lower electrode was grounded. The pressure was
measured with ultra-low pressure sensor (EdgeLight ELPR-5). LabVIEW
acted as interface to collect the data. The silicone oil was pumped
into the channel with a Harvard syringe pump. The outlet of the
channel was open to the air and fixed at certain position.
Example 3
Pressure Measurement
[0038] The origin of the measured quantity
.DELTA.P''=.DELTA.P'-.DELTA.P is depicted in FIG. 4 and FIG. 5.
Formation of dipolar molecular filaments provided resistance to the
flow and additional energy was required to maintain the flow rate.
This is reflected by the increment in the pressure difference which
is nothing more than the increment of the input energy density.
This additional part of energy density was used to (partially)
break the dipolar filaments, and therefore should be equal to or
smaller than the electric energy density of the filament
structure.
Example 4
Estimate Model
[0039] Based on the physical picture established in Example 3, the
following model estimates the effect. Free energy density equals
the filaments' dipole-field interaction and dipole-dipole repulsive
interaction. Minimizing free energy with respect to the number
density of the filaments provides an equilibrium configuration and
the corresponding energy density W that equals the measured
increase in pressure difference .DELTA.P'' based on
constant-flow-rate measurement, wherein .DELTA.P'' is the
additional energy density required for breaking the filaments when
the field is applied.
[0040] FIG. 6 shows the effective surface charge density at the two
water oil interfaces separated at the gap distance. The charge
density may be directly related to the number density of filament
dipoles. To calculate energy density, using Gauss's law the
displacement outside the oil layer will always be 0, which means
that the presence of the electrodes and the dielectric constant of
the water membrane have no effect on energy, and only the
dielectric constant of oil counts.
[0041] The electric free energy at a field of E can be written as a
function of the surface charge density .sigma.:
f ( .sigma. ) = 1 2 0 .sigma. 2 - .sigma. E ( 1 ) ##EQU00002##
with a minimum at:
.sigma.=.epsilon..epsilon..sub.0E (2)
[0042] And the resulting volume density of the free energy is:
- 1 2 0 E 2 ( 3 ) ##EQU00003##
[0043] The measured change in pressure as a function of the applied
electric field E can then be expressed as .DELTA.P''=8.8E.sup.2,
and the coefficient can be obtained directly from experiment for
comparison.
Example 5
Measurement and Observations
[0044] Samples with gap width of 0.5 mm, 0.75 mm and 1 mm were
measured for water-silicone oil systems. FIGS. 6-9 show that, once
high voltage is applied, the pressure difference increases
immediately, and then falls back when the voltage was removed.
Measurement continued until breakdown occurs (6 kV for 1 mm gap in
water-silicone oil system). Without the water-absorbing membrane or
with water-absorbing membrane but no water inside, no change in the
pressure difference was observed. For water-decane system with 1 mm
gap (FIG. 10) no change in pressure difference is observed, which
implies no water molecular filament forms, because decane is more
hydrophobic than silicon oil. The electric field can provide a
finite driving energy which is smaller than the energy barrier for
a water molecule to penetrate into decane, and thus the filament
cannot be formed. However, in the case of silicon oil, this energy
barrier is small and the filament can therefore be induced by the
applied electric field. .DELTA.P'' is measured as a function of the
voltage applied. FIG. 11 shows the average of the results under
high voltage. .DELTA.P'' shows a quadratic voltage dependence at
low voltage range. Under the same applied voltage, .DELTA.P''
decreases as the gap size becomes larger. When the applied voltage
is higher, .DELTA.P'' gradually adopts linear voltage dependence
possibly because quadratic dependence is a direct consequence of
the free energy minimization, based on the assumption sufficient
water molecules are used to form new filaments as required. As
absorbed water gradually exhausts with voltage increases, the
number of the filaments saturates. Therefore, the electric energy
density of the filaments becomes linearly dependent on the voltage,
leading to the linear dependence of .DELTA.P''.
Example 6
Pressure Difference Plotted as the Function of E.sup.2 and
Observations
[0045] For all three samples of the water-silicone oil system, the
voltage is normalized with the gap size, and average results
measured in Example 5 are re-plotted as a function of E.sup.2 (FIG.
12). All three curves collapse at low field range, indicating
.DELTA.P'' mainly depends on the applied electric field and has
little relationship with the gap size. The change in pressure
difference is proportional to E.sup.2. From linear fitting, the
coefficient is around 6, which corresponds to the value calculated
from the previous electric energy, around 8.8. The measured
coefficient is smaller than the calculated value, as expected.
[0046] The origin of .DELTA.P'' cannot be due to the generation of
a water layer between the silicone oil and the electrodes since
that would introduce a slip boundary for the carrier flow and hence
reduce the pressure difference. With the presence of a normal
electric field, there can also be instability at the water-oil
interface, owing to the dielectric constant contrast between the
two media. However, the instability would allow water droplets to
penetrate into silicone oil, decreasing the pressure difference
since water has a lower viscosity than that of silicone oil. The
comparative Experiments confirmed water must be responsible for the
measured electrorheological effect resulting from dipolar molecular
filaments.
Example 7
Rheometer Measurement
[0047] The effect observed in Example 6 is confirmed by rheometer
measurement. Haake RS18 mm diameter circular rotating rheometer
measures the molecular ER effect in the water-silicone oil system
(FIG. 13). The voltage is applied through the two electrodes (the
upper one rotates whereas the lower one is fixed). The gap is set
to be 1 mm and filled with silicone oil. The electrode is covered
with water-absorbed polyester-based membrane. 1 kV rectangular wave
was applied. Once the electric field is applied, the shear stress
increases quickly and can reach 80 Pa before falling back when the
electric field is removed (FIG. 14).
[0048] In the context of the relationship between yield stress and
strain, the consistency with the rheometer measurement is verified.
Measured yield stress .tau..sub.0 is proportional to the electric
energy density W. .tau.=a.epsilon. for a linear strain-stress
relation, where a is the constant and .epsilon. is the strain. It
follows that
W = 1 2 a 2 ##EQU00004##
and .tau.=2W/.epsilon.. The yield stress is the stress where the
yield point .epsilon..sub.0 is reached, and therefore .tau..sub.0
=2W/.epsilon..sub.0 (FIG. 15). A yield stress of .about.88 Pa with
a 1 kV/mm applied field is predicted, which is coincides with the
preliminary measurement.
[0049] It will be understood that many additional changes in the
details, materials, steps and arrangement of parts, which have been
herein described and illustrated to explain the nature of the
subject matter, may be made by those skilled in the art within the
principle and scope of the instant subject matter as expressed in
the appended claims.
Example 8
Molecular Dynamics Simulation
[0050] MD simulation was performed for a system composed of silicon
oil (90 wt %) and water (10 wt %) uniformly mixed. See, FIG. 16 aMD
snapshot showing the initial configuration of the simulation.
Relatively uniform distribution of water molecules was realized by
randomly inserting water molecules into the intervals of the
silicone oil chains (omitted from the Figure to obtain a clear
view). While the simulation was performed for a system composed of
90 wt % silicon oil and 10 wt % water, it is also contemplated that
the amount of silicon oil can range from 85 wt % to 95 wt %;
likewise the amount of water can range from 5 wt % to 15 wt %.
[0051] An electric field was applied along the direction shown by
the arrow in FIG. 17. Through simulations, the dipoles of the water
molecules in the filaments are mostly aligned along the electric
field direction, and these filaments represent giant dipoles
bridging the gap. This particular structure gives rise to the ER
effect as observed in each of the examples.
[0052] This uniform water-oil mixture with low water fraction is a
new type of all-liquid ER fluid because of the absence of a solid
(particle) phase which is the key component in conventional ER and
GER fluids. It should be noted that the system is capable of
functioning with various fractions. Moreover, the device to realize
the all-liquid ER effect can become extremely simple with two
electrically insulated electrodes and two side walls as the
channel. In this case, no water reservoirs would be needed.
Example 9
Fabrication of Microfluidic Measurement
[0053] Samples with small gap size of .about.5 .mu.m were also
examined using the apparatus described below. It was found
.DELTA.P'' increased to 2.2 kPa at an applied voltage of 1.6 kV.
The sample of 5 .mu.m gap was made of two water-penetrable AAO
membranes sandwiched by two metal mesh electrodes, as shown in FIG.
18.
[0054] The apparatus s made of three major parts: metallic mesh
electrodes with mesh size of 90 .mu.m, AAO membrane and fluid
channel. See FIGS. 18 and 19. The high voltage was applied directly
on the metallic mesh electrodes. The fluid channel was formed by
two AAO membranes (64 .mu.m thickness), separated by spacers that
were made by PS (polystyrene) microspheres and the gap size was
determined by the size of the spacer. PS microspheres with diameter
of 5.15 .mu.m were used. A pressure sensor is put near the
electrodes to measure the pressure difference. Epoxy sealing is
used as the side walls of channel. Uniform pores with diameter of
100 nm on the AAO membrane were used for water supply. Ceramic
(Resbond 920) was put inside the hole of PMMA film to serve as
water reservoir. PMMA film (24 mm.times.10 mm) with thickness of 1
mm was fabricated by the laser engraving machine (Universal Laser
System).
[0055] The upper PMMA film has three holes. The large hole with
diameter of 6 mm was used to hold the ceramic and two small holes
with diameter of 0.9 mm were used for connection of stainless steel
tubes. The bottom PMMA film just had one large hole for water
supply. Firstly, metal mesh and AAO were attached to the PMMA films
with epoxy. Then two stainless steel tubes with diameter of 0.9 mm
were inserted into the two small holes in the PMMA to be the fluid
inlet and outlet. Epoxy was covered near the tube for sealing. PS
microspheres with diameter 5.15 .mu.m were used as spacer to
separate two AAO membranes. At last two PMMA films were stick
together by epoxy and ceramic was put inside the large hole to
store water.
Example 10
Measurement Protocol
[0056] Measurement of this sample of Example 9 was performed
similarly to that set forth in Example 2, except that the pressure
difference was measured using the digital pressure meter (CWY50).
In order to put forward the application of the all liquid ER effect
into real application, parallel-plate channels with small gap sizes
.about.5 .mu.m to achieve a larger electric field induced pressure
difference were used. As expected, an increment in the pressure
difference was observed which is one order of magnitude larger than
those for the large samples. The results, FIG. 20,(measured
.DELTA.P'' as a function of the voltage applied for small gap
size(5.15 .mu.m) sample). indicate a trend of quadratic dependence
on the applied electric field in small field region, and a linear
dependence as the applied voltage increases. Saturation behavior in
the pressure difference was observed in large field region. Similar
to previous cases, this observed pressure difference arises from
the yield stress of the water dipolar filaments. The largest
pressure increment measured is .about.2.2 kPa. Such effect is gone
when silicone oil is substituted by decane. It has to be noted that
the distance between the two electrodes is still large due to the
sandwiched AAO membranes, compared with the channel size. The
quadratic field dependence can imply that the yield stress can
reach the order of MPa when the distance between the two electrodes
decreases. This corresponds to an electric energy density higher
than that of any GER materials.
* * * * *