U.S. patent application number 13/647242 was filed with the patent office on 2013-04-11 for continuous flow synthesis of nanomaterials using ionic liquids in microfluidic reactors.
This patent application is currently assigned to UNIVERSITY OF SOUTHERN CALIFORNIA. The applicant listed for this patent is University of Southern California. Invention is credited to Richard Brutchey, Steven Chu, Laura Lazarus, Noah Malmstadt, Brandon Marin, Carson Riche, Astro S.-J. Yang.
Application Number | 20130087020 13/647242 |
Document ID | / |
Family ID | 48041203 |
Filed Date | 2013-04-11 |
United States Patent
Application |
20130087020 |
Kind Code |
A1 |
Brutchey; Richard ; et
al. |
April 11, 2013 |
CONTINUOUS FLOW SYNTHESIS OF NANOMATERIALS USING IONIC LIQUIDS IN
MICROFLUIDIC REACTORS
Abstract
A method for manufacturing metal nanoparticles includes the use
of a microfluidic device. The microfluidic device has a first
channel having a first inlet; a second channel having a second
inlet; a third channel having a third inlet; and a main channel
having a main inlet and an outlet. The first channel, second
channel, and third channel all lead into the main channel. The
method involves injecting a solution of a metal/ligand into the
first inlet, injecting a solution of a reducing agent into the
second inlet, injecting a solvent comprised of an ionic liquid into
the third inlet, and injecting an inert carrier into the main
inlet. The solution of the metal/ligand, the solution of the
reducing agent, the solvent and the inert carrier are combined
together in the main channel, and the metal/ligand and the reducing
agent are reacted for a time sufficient to form a metal
nanoparticle.
Inventors: |
Brutchey; Richard; (Los
Angeles, CA) ; Malmstadt; Noah; (Altadena, CA)
; Lazarus; Laura; (Long Beach, CA) ; Yang; Astro
S.-J.; (Los Angeles, CA) ; Riche; Carson;
(Zionsville, PA) ; Chu; Steven; (Honolulu, HI)
; Marin; Brandon; (West Covina, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Southern California; |
Los Angeles |
CA |
US |
|
|
Assignee: |
UNIVERSITY OF SOUTHERN
CALIFORNIA
Los Angeles
CA
|
Family ID: |
48041203 |
Appl. No.: |
13/647242 |
Filed: |
October 8, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61544447 |
Oct 7, 2011 |
|
|
|
Current U.S.
Class: |
75/370 |
Current CPC
Class: |
B22F 1/0018 20130101;
B22F 3/003 20130101; B22F 9/24 20130101 |
Class at
Publication: |
75/370 |
International
Class: |
B22F 9/18 20060101
B22F009/18 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with Government support under Grant
No. CMMI-0926969, awarded by the National Science Foundation. The
Government has certain rights in the invention.
Claims
1. A method for manufacturing metal nanoparticles by the use of a
microfluidic device, the microfluidic device comprising: a first
channel having a first inlet; a second channel having a second
inlet; a third channel having a third inlet; and a main channel
having a main inlet and an outlet, wherein the first channel,
second channel, and third channel all lead into the main channel,
the method comprising the steps of: injecting a solution of a
metal/ligand into the first inlet, injecting a solution of a
reducing agent into the second inlet, injecting a solvent comprised
of an ionic liquid into the third inlet, and injecting an inert
carrier into the main inlet, combining the solution of the
metal/ligand, the solution of the reducing agent, the solvent and
the inert carrier together in the main channel, and reacting the
metal/ligand and the reducing agent for a time sufficient to form a
metal nanoparticle.
2. The method of claim 1, wherein the microfluidic device is
comprised of a polymeric material.
3. The method of claim 2, wherein the polymeric material comprises
silicon.
4. The method of claim 3, wherein the polymeric material is
poly(dimethylsiloxane).
5. The method of claim 1, wherein the first channel, the second
channel, the third channel, and the main channel each have a width
in a range of from about 100 .mu.m to about 2000 .mu.m.
6. The method of claim 1, wherein the first channel, the second
channel, the third channel, and the main channel each have a depth
in a range of from about 20 .mu.m to about 200 .mu.m.
7. The method of claim 1, wherein the first channel, the second
channel, the third channel, and the main channel have a hydrophobic
coating.
8. The method of claim 7, wherein the coating comprises a
fluoropolymer.
9. The method of claim 1, wherein the metal/ligand solution is
comprised of a mixture of a metal and a ligand capable of
stabilizing the metal.
10. The method of claim 9, wherein the metal is at least one
selected from the group consisting of gold, silver, cobalt, copper,
platinum, and palladium.
11. The method of claim 9, wherein the ligand is comprised of an
ionic liquid.
12. The method of claim 11, wherein the ionic liquid is an
imidazolium based compound.
13. The method of claim 1, wherein the reducing agent is an
imidazolium based borohydride.
14. The method of claim 1, wherein inert carrier comprises a
hydrophobic liquid.
15. The method of claim 14, wherein the hydrophobic liquid
comprises a fluorocarbon.
16. The method of claim 1, wherein a ratio of the rate of injection
of the inert carrier compared to the rate of injection of the
solution of the metal/ligand, the solution of the reducing agent
and the solvent is from about 2:1 to about 20:1.
17. The method of claim 16, wherein a flow rate of the inert
carrier is about 1 mL/hour to about 10 mL/hour.
18. The method of claim 1, wherein a flow rate of the inert carrier
is such that when the solution of the metal/ligand, the solution of
the reducing agent and the solvent are combined with the inert
carrier in the main channel, a droplet comprised of metal/ligand,
the reducing agent and the solvent is formed.
19. The method of claim 1, wherein a ratio of the rate of injection
of the solution of the metal/ligand to the solvent is from about
1:1 to about 3:1.
20. The method of claim 1, wherein a ratio of the rate of injection
of the solution of the reducing agent to the solvent is from about
1:1 to about 3:1.
21. The method of claim 1, wherein a ratio of the rate of injection
of the solution of the metal/ligand to the solution of the reducing
agent is from about 0.5:1 to about 2:1.
22. The method of claim 1, wherein the metal nanoparticle formed
has a diameter of from about 3 nm to about 6 nm.
23. The method of claim 1, wherein the metal nanoparticle formed
has a spherical shape.
24. The method of claim 1, wherein the time of the reaction of
metal/ligand and the reducing agent is from about 5 to about 60
seconds.
25. The method of claim 1, wherein after reacting the metal/ligand
and the reducing agent, the nanoparticle formed is deposited
through the outlet of the main channel.
Description
CROSS REFERENCE TO PROVISIONAL APPLICATION
[0001] The present application is based upon and claims the benefit
of priority from Provisional U.S. Patent Application No. 61/544,447
(Attorney docket No. 28080-679) filed on Oct. 7, 2011, the entire
contents of which are incorporated by reference herein.
BACKGROUND
[0003] There is a rapidly growing demand for metal nanoparticles.
Nanoparticles are used in a wide variety of industries, such as
pharmaceuticals, renewable energy, textiles, and cosmetics. The
global market was projected to be $220 billion in 2010, with 61%
attributable to fabrication. There is a critical need for
innovative nanomanufacturing approaches that minimize energy use,
emissions, waste, all while maximizing the quality of the
product.
[0004] However, nanoparticle manufacturing is still commonly
performed on a batch-by-batch, lab-scale process. Control over
these variables is difficult in large-scale batch reactors because
of limitations in heat and mass transport. As such, the scalability
of this method is limited and mitigation of these limitations
translates to higher costs. Nanoparticles may also be produced in
small volume batch reactions although difficulties controlling and
reproducing size, size distribution, and morphology are typical. As
novel applications for nanoparticles continue to emerge, there is
an increasing need for approaches to nanomanufacture these
materials using inexpensive, rapid, and reproducible methods that
have minimal impact on the environment.
[0005] Reactor miniaturization via microfluidic technology has
enabled the continuous flow synthesis of a large number of
molecules and nanomaterials. Microfluidic reactors offer several
advantages over traditional batch scale syntheses; namely,
continuous throughput, superior reaction control, and minimal
solvent waste and byproduct generation. Such control is made
possible by improved heat and mass transport within the
microfluidic channels that result from high surface area-to-volume
ratios, in addition to fast reagent mixing. Moreover, microfluidic
devices allow for reduction of environmental risks associated with
nanofabrication by allowing small-volume, on-demand syntheses that
also result in higher yields and less by-product generation.
SUMMARY
[0006] The present disclosure is directed toward a method to
fabricate monodisperse metal nanoparticles using a simple
continuous flow microfluidic device in tandem with
imidazolium-based ionic liquids.
[0007] In one example of the present disclosure, a method for
manufacturing metal nanoparticles by the use of a microfluidic
device is described. The microfluidic device comprises a first
channel having a first inlet; a second channel having a second
inlet; a third channel having a third inlet; and a main channel
having a main inlet and an outlet. The first channel, second
channel, and third channel all lead into the main channel. The
method comprises the steps of injecting a solution of a
metal/ligand into the first inlet, injecting a solution of a
reducing agent into the second inlet, injecting a solvent comprised
of an ionic liquid into the third inlet, and injecting an inert
carrier into the main inlet. The solution of the metal/ligand, the
solution of the reducing agent, the solvent and the inert carrier
is combined together in the main channel, and the metal/ligand and
the reducing agent are reacted for a time sufficient to form a
metal nanoparticle.
[0008] Additional advantages and other features of the present
disclosure will be set forth in part in the description which
follows and in part will become apparent to those having ordinary
skill in the art upon examination of the following or may be
learned from the practice of the disclosure. The advantages of the
disclosure may be realized and obtained as particularly pointed out
in the appended claims.
[0009] As will be realized, the present disclosure is capable of
other and different examples, and its several details are capable
of modifications in various obvious respects, all without departing
from the disclosure. Accordingly, the drawings and description are
to be regarded as illustrative in nature, and not as
restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a representation of a microfluidic device used to
synthesize nanoparticles according to one example of the present
disclosure.
[0011] FIG. 2 is a representation of a portion of a microfluidic
device used to synthesize nanoparticles according to another
example of the present disclosure.
[0012] FIGS. 3a-b are a TEM micrograph and UV-Vis spectrum of
nanoparticles synthesized according to one example of the present
disclosure.
[0013] FIG. 4 is an XRD pattern and SAED pattern of nanoparticles
synthesized according to one example of the present disclosure.
DETAILED DESCRIPTION
[0014] Illustrative examples are now discussed and illustrated.
Other examples may be used in addition or instead. Details which
may be apparent or unnecessary may be omitted to save space or for
a more effective presentation. Conversely, some examples may be
practiced without all of the details which are disclosed.
[0015] FIG. 1 shows a diagram of a microfluidic device used for the
synthesis of monodisperse nanoparticles according to an example of
the present disclosure.
[0016] The microfluidic device 100 shown in FIG. 1 includes a first
channel 10 having a first inlet 11, a second channel 20 having a
second inlet 21, a third channel 30 having a third inlet 31, and a
main channel 40 having a main inlet 41 and an outlet 42. The first
channel 10, second channel 20, and third channel 30 all lead into
the main channel 40.
[0017] The microfluidic device 100 may be any suitable material for
use in synthesis of nanoparticles. In some examples, the
microfluidic device 100 is comprised of a polymeric material. The
polymeric material may include silicon, for example,
poly(dimethylsiloxane) (PDMS).
[0018] The microfluidic device 100 may be fabricated through a
standard photolithography process. In some examples, the
photolithography process consists of a cast PDMS layer bonded to a
bare PDMS substrate. The PDMS stamp is cast onto the mold and cured
at 65.degree. C. for at least 2 hours to recover PDMS surface
hydrophobicity.
[0019] In some examples, the first channel 10, the second channel
20, the third channel 30, and the main channel 40 have a
hydrophobic coating. The hydrophobic coating may be any coating
suitable for use in the microfluidic device may include a
fluoropolymer or a silicon containing compound. For example, before
use, the device may be silanized with
trichloro(1H,1H,2H,2H-per-fluorooctyl)silane (97%, Sigma-Aldrich)
for 20 min to make the first, second, third and main channel
surfaces hydrophobic and prevent device fouling by AuNP adsorption
on the channel walls. In other examples, the microfluidic device
may be comprised of glass, silicon and polycarbonate.
[0020] The device may be any size suitable to allow for the
formation of monodisperse nanoparticles. In some examples, the
first channel 10, the second channel 20, the third channel 30, and
the main channel 40 each have a width in a range of from about 100
.mu.m to about 2000 .mu.m, and have a depth in a range of from
about 20 .mu.m to about 200 .mu.m. For example, the microfluidic
device 100 of the present disclosure as shown in FIG. 1 measures
3.times.5 cm overall and the channel widths and depths are 600 and
95 .mu.m, respectively, with a total channel volume of 7.6
.mu.L.
[0021] The method forming the nanoparticles may comprise the steps
of injecting a solution of a metal/ligand into the first inlet,
injecting a solution of a reducing agent into the second inlet,
injecting a solvent comprised of an ionic liquid into the third
inlet, and injecting an inert carrier into the main inlet.
[0022] The metal/ligand solution may include a mixture of a metal
and a ligand capable of stabilizing the metal. The metal may
include any metal capable of forming monodisperse nanoparticles. In
some examples, the metal may be at least one selected from gold,
silver, cobalt, copper, platinum, palladium and ruthenium.
[0023] The ligand capable of stabilizing the metal may include an
ionic liquid (IL). In certain examples, the IL may be an
imidazolium based compound. Imidazolium based ILs act as a
dual-function solvent system and stabilizing ligand for metal
nanoparticles. ILs may be used as solvents for synthetic reactions
in poly(dimethylsiloxane) (PDMS) microfluidic devices since they do
not suffer from the PDMS incompatibility that limits the use of
traditional organic solvents. Moreover, ILs are nonflammable and
possess negligible vapor pressures, in addition to having the
ability to stabilize metal nanoparticles because of their high
ionic charge, high dielectric constant, and ability to form
supramolecular hydrogen-bonded networks in the condensed phase,
which may serve as structure directing networks for nanoparticle
growth.
[0024] In some examples, 1-butyl-3-methylimidazolium
tetrafluoroborate (BMIM-BF4) may be used as the ligand. In other
examples, 1-butyl-3-methylimidazolium
bis-(trifluoromethylsulfonyl)imide (BMIM-Tf2N) may be used as the
ligand, since BMIM-Tf2N exhibits greater stability of the
bistriflimide anion compared to tetrafluoroborate. Further, the
hydrophobicity of BMIM-Tf2N, makes it easier to obtain in purer
form.
[0025] In the second channel 20, the reducing agent added may be
any suitable reducing agent capable of reacting with the
metal/ligand to produce a nanoparticle. For example, a borohydride,
such as sodium borohydride (NaBH4) is an acceptable reducing agent.
In other examples, the reducing agent is an imidazolium based
borohydride, such as 1-butyl-3-methylimidazolium borohydride
(BMIM-BH4). Substituting BMIM-BH4 for NaBH4 may provide improved
reducing agent solubility in the ionic liquid without the
possibility of forming sodium-containing byproducts.
[0026] In the third channel 30, a solvent may be injected via the
third input 31. The solvent should be one capable of solubilizing
the metal/ligand and reducing agent, and allow for the reaction to
produce nanoparticles to proceed. In some examples, the solvent may
be used to insure that reagent mixing occurs only by interdiffusion
between laminar streams, and not before the mixture of the
metal/ligand and reducing agent reaches the main channel 40. In
some examples, the solvent is 1-butyl-3-methylimidazolium
tetrafluoroborate (BMIM-BF4; 98+%, Alfa Aesar).
[0027] The inert carrier is used to carry the reactants, e.g., the
metal/ligand and reducing agent, along the main channel 40 and out
the outlet 42 where the products may be collected. The rates of
injection of the metal/ligand, reducing agent, and solvent compared
to the flow rate of the inert carrier may have an influence on the
formation of the nanoparticles. Although more controlled than
mixing in a macroscale batch reactor, flow focused laminar mixing
within microchannels is diffusion limited, and concentration
gradients can lead to polydispersity in nanoparticle syntheses. One
solution to this problem is the use of droplet flows. Droplet flow
microfluidic reactors allow for the generation of discrete droplets
that are separated from one another by the inert carrier. The inert
carrier may be immiscible with the metal/ligand, reductant and
solvent.
[0028] In this configuration, mixing within the droplet is rapid
and can be precisely controlled, unlike in conventional macroscale
batch reactors where mixing is almost always turbulent and not
well-defined. Droplet flows can eliminate concentration dispersion
and maintain a constant ratio of reagents in all droplets.
Convective mixing within these droplets has been shown to decrease
the mixing time by 2 orders of magnitude as compared to diffusive
mixing between coflowing laminar streams. The rate of mixing and
type of mixing in discrete droplets separated by an immiscible
carrier phase can be systematically tuned through varying the flow
rates of the different phases.
[0029] In the present disclosure, the ratio of mixing of the ratio
of the rate of injection of the inert carrier compared to the rate
of injection of the solution of the metal/ligand, the solution of
the reducing agent and the solvent is from about 2:1 to about 20:1.
The ratio of the rate of injection of the solution of the
metal/ligand to the solvent, the reductant to solvent, or the
metal/ligand to reductant is from about 1:1 to about 3:1. In other
examples, the ratio of the rate of injection of the metal/ligand to
the solution of the reducing agent is from about 0.5:1 to about
2:1. These injection rates may allow for the formation of droplets
as discussed above. For example, in the microfluidic device 200 as
is shown in FIG. 2, the metal/ligand is injected into the first
inlet 11 and passes through the first channel to combine with the
reductant and solvent, which were passed through the second and
third channels, respectively. The combination is then passed into
the main channel 40 where the inert carrier, which was injected via
the main inlet 41, is located. Due to the differences in viscosity
and solubility, the combination forms a droplet 50, which comprises
the combination of metal/ligand, reductant and solvent. In this
droplet, the metal/ligand and the reducing agent are reacted for a
time sufficient to form a metal nanoparticle. After formation of
the nanoparticle, the nanoparticle is deposited through the outlet
of the main channel 40 and out the outlet 42 (see FIG. 1).
[0030] The reaction time for formation of the nanoparticles is
short. In some examples, the time of the reaction of metal/ligand
and the reducing agent is from about 5 to about 60 seconds. The
faster the reaction time, the more nanoparticles that may be
formed.
[0031] The size of the metal nanoparticles formed has a narrow
range. In some examples, the metal nanoparticle formed has a
diameter of from about 3 nm to about 6 nm. The shape of the metal
nanoparticle formed may be spherical.
EXAMPLES
[0032] As stated above, microfluidic-based syntheses of the present
disclosure are a means to efficiently and reliably fabricate
nanoparticles. The examples below are.
Example 1
[0033] A microfluidic device according to one example was
fabricated through a standard photolithography process and consists
of a cast PDMS layer bonded to a bare PDMS substrate. The device
measures 3.times.5 cm overall and the channel widths and depths are
600 and 95 .mu.m, respectively, with a total channel volume of 7.6
.mu.L. Before use, the device was silanized with
trichloro(1H,1H,2H,2H-per-fluorooctyl)silane (97%, Sigma-Aldrich)
for 20 min to make the channel surface hydrophobic and prevent
device fouling by gold nanoparticles (AuNP) adsorption on the
channel walls. A stream of pure BMIM-BF4 was injected between the
two reagent streams (HAuCl4/1-methylimidazole and NaBH4 in
BMIM-BF4) to insure that reagent mixing occurred only by
interdiffusion between laminar streams. This pure BMIM-BF4 stream
and the two reagent streams were injected by syringe pump at a flow
rate ratio of 5:9:9 via inlets I, II, and III, respectively. An
inert polychlorotrifluoroethylene oil (Halocarbon 6.3 oil; River
Edge, N.J.) was introduced via the main inlet 41 (see FIG. 1) at a
flow rate of either 2070 .mu.L/h or 7000 .mu.L/h. These inert
carrier oil flow rates defined two flow regimes--at the lower flow
rate, the central IL stream remained continuous through the device
while at the higher flow rate it broke up into droplets (the
transition between flow regimes occurred at an inert oil flow rate
of about 3000 .mu.L/h). The reaction products were collected
continuously from outlet 42 and quenched/precipitated into a
reservoir containing ethanol.
[0034] The AuNPs were isolated by centrifugation (6000 rpm, 5 min)
followed by washing twice with fresh ethanol to remove excess
BMIM-BF.sub.4. The isolated AuNPs were redispersed in hexanes and
1-dodecanethiol (5-10 .mu.L/mL hexanes) by sonication, which gave
red suspensions that were stable for months. The resulting AuNPs
were analyzed by powder X-ray diffraction (XRD), selected area
electron diffraction (SAED) and UV-Vis spectroscopy. The size,
morphology, and size distribution of the resulting AuNPs were
characterized by transmission electron microscopy (TEM).
[0035] Comparatively, the gold nanoparticles that we have obtained
are monodisperse with a mean diameter of 4.38.+-.0.53 nm
(.sigma./.mu..sub.d=12.1%) and form 20 arrays as determined by
transmission electron microscopy (TEM) (see FIG. 3a). These
particles were overwhelmingly spherical with only 15.0% having a
roundness, defined as (4.times.particle area)/[.pi..times.(major
axis length).sup.2], less than 0.85. UV-Vis spectra of the deep red
AuNP suspensions gave relatively narrow surface plasmon bands
centered at d=518.5 nm, typical of AuNPs that are largely
non-agglomerated (see FIG. 4). The XRD pattern of the AuNPs can be
assigned to the face centered cubic (fcc) structure of gold (JCPDS
no. 04-0784), with a lattice parameter of a=4.07 A.about.that
matches literature values. The crystallinity of the AuNPs was
further confirmed by SAED analysis. The diffuse diffraction rings
produced by an ensemble of nanoparticles were indexed to the
characteristic {111}, {200}, {220}, and {311} diffraction planes of
fcc gold (inset, FIG. 4), and the lattice parameter corroborates
that calculated by powder XRD. Energy dispersive X-ray
spectroscopic analysis suggests that the majority of the
1-methylimidazole and BMIM-BF.sub.4 is displaced from the AuNP
surface upon work-up with thiol, with the analyses for nitrogen and
fluorine giving baseline integrated signal relative to that of
sulfur.
[0036] Flow focusing by inert carrier oil has a dramatic effect on
the size and morphological fidelity of the AuNPs. When the flow
rate of the inert oil is decreased such that the IL stream no
longer forms droplets, particles are larger (5.65 f 1.03 nm) and
more polydisperse (v/.mu.d=18.2%). The particles were also less
spherical, with 23.4% having a roundness less than 0.85. In either
flow-focused device geometry, the inert oil forces the two reagent
streams, and the center BMIM-BF.sub.4 stream separating them, down
to narrower widths. As a result, the diffusion lengths needed for
the two reagents to mix in the center BMIM-BF.sub.4 stream are
reduced. To illustrate the importance of flow focusing, an
analogous microfluidic device was constructed without the
additional carrier oil inlet (i.e., inlet 41 in FIG. 1). The three
streams of BMIM-BF.sub.4, HAuCl.sub.4/1-methylimidazole, and
NaBH.sub.4 were introduced via syringe pump at flow rates of 500,
900, and 900 .mu.L h-1 1 through inlets 11, 21, and 31,
respectively. Laminar flow is observed under these conditions, with
AuNP formation discernible further down channel as the center
stream turns purple in color. Using this laminar flow device
configuration, the AuNPs are more polydisperse and have a larger
mean diameter (6.25 f 1.29 nm; .sigma./.mu.d=20.6%), in addition to
being more spheroidal in shape with 28.2% having a roundness less
than 0.85. Thus, it is likely that the decreased interdiffusion
distance between reagent streams in the fast inert carrier
flow-focused geometry leads to faster mixing, which in turn
constrains the nucleation burst, resulting in less polydisperse
particles.
Example 2
[0037] Formation of Microfluidic Device:
[0038] A stable droplet formation of the viscous BMIM-Tf.sub.2N
ionic liquid within a continuous fluorocarbon oil phase,
poly(chlorotrifluoroethylene)(PCTFE), was achieved by modifying the
interior surfaces of preassembled PDMS devices with a fluoropolymer
coating via a previously reported initiated chemical vapor
deposition (iCVD) method. Briefly, the
poly(1H,1H,2H,2H-perfluorodecyl acrylate-co-ethylene glycol
diacrylate) coating is deposited in a vapor phase polymerization
process where monomer molecules and initiator radicals polymerize
via a free-radical chain mechanism on the interior surfaces of the
preassembled channels. Coated devices performed with no signs of
degradation or delamination for at least 24 h.
[0039] Microfluidic Synthesis of Au Nanoparticles.
[0040] Solutions of HAuCl.sub.4 (10 mM), 1-methylimidazole (5 M),
and BMIM-BH.sub.4 (0.1 M) were prepared in BMIM-Tf.sub.2N with
stirring at 25.degree. C. Equal volumes of HAuCl.sub.4 and
1-methylimidazole solutions were thoroughly mixed before being
introduced on device via syringe pump. Syringes and outlet tubing
interfaced with the microfluidic device via PEEK tubing (I.D.=0.762
mm) and exited the device via silicon tubing (I.D.=1.02 mm).
Reagent solutions of HAuCl.sub.4/1-methylimidazole and
BMIM-BH.sub.4 were injected through inlets 11 and 21, respectively.
A pure BMIM-Tf.sub.2N buffer stream was injected between the two
reagent streams via inlet 31. All dispersed phase reagents had a
flow rate of 0.5 mL h.sup.-1. The immiscible carrier oil,
poly(chlorotrifluoroethylene) (PCTFE) was injected into the main
channel 40 with a flow rate of 10 mL h.sup.-1 via inlet 41. The
samples exited the microfluidic device and were collected for 30
min in an empty collection tube (residence time=60 s) where they
separated into two distinct phases and the oil phase was removed
prior to workup. The AuNPs were precipitated by centrifugation
after the addition of ethanol (4 mL). The colorless supernatant was
replaced with fresh ethanol and the mixture was sonicated for 2 min
using a probe sonicator fitted with a microtip at 50% duty cycle
(Sonifier S-450A analog ultrasonic processor, Branson). The AuNPs
were again isolated by centrifugation and finally redispersed in
hexanes and 1-dodecanethiol (10-20 .mu.L mL.sup.-1 hexanes) with
probe sonication for 1 min.
[0041] Microfluidic Synthesis of Ag Nanoparticles.
[0042] Solutions of AgBF.sub.4 (40 mM), 1-methylimidazole (1.2 M),
and BMIM-BH.sub.4 (200 mM) were prepared in BMIM-Tf.sub.2N with
stirring at 25.degree. C. Equal volumes of AgBF.sub.4 and
1-methylimidazole solutions were thoroughly mixed before being
introduced on device via syringe pump. Reagent solutions of
AgBF.sub.4/1-methylimidazole and BMIM-BH.sub.4 were injected
through inlets 11 and 31, respectively (see FIG. 2). Solutions
containing the AgBF.sub.4 were protected from light until before
the reaction. A pure BMIM-Tf.sub.2N buffer stream was injected
between the two reagent streams via inlet 21. All dispersed phase
inlets had a flow rate of 0.5 mL h.sup.-1. The immiscible carrier
oil was injected into the main channel with a flow rate of 10 mL
h.sup.-1 viainlet 1. The AgNPs were isolated by phase transfer
whereby the AgNP dispersion in BMIM-Tf.sub.2N was collected into an
organic phase containing hexanes (2 mL), ethanol (2 mL), 1-
dodecanethiol (50 .mu.L), and trioctylamine (25 .mu.L). The samples
were collected for 30 min (residence time=2 min 45 s) and the
colored organic layer containing AgNPs was transferred to a new
centrifuge tube. The AgNPs were precipitated by centrifugation
after the addition of methanol (3 mL). The colorless supernatant
was replaced with ethanol and the mixture was sonicated for 2 min
using a probe sonicator fitted with a microtip at 50% duty cycle.
The AgNPs were again isolated by centrifugation and finally
redispersed in hexanes (1-2 mL) with probe sonication for 1
min.
[0043] Batch Synthesis of Au and Ag Nanoparticles.
[0044] Solutions of HAuCl.sub.4 (10 mM), 1-methylimidazole (5 M),
and BMIM-BH.sub.4 (0.1 M) were prepared in BMIM-Tf.sub.2N with
stirring at 25.degree. C. Solutions of HAuCl.sub.4 (0.25 mL) and
1-methylimidazole (0.25 mL) were thoroughly mixed. Thereafter, 0.5
mL of the BMIM-BH.sub.4 solution was rapidly injected resulting in
an immediate color change. After stirring for 1 min the AuNPs were
precipitated by centrifugation with the addition of ethanol (4 mL).
The colorless supernatant was replaced with fresh ethanol and the
mixture was sonicated for 2 min using a probe sonicator fitted with
a microtip at 50% duty cycle. The AuNPs were again isolated by
centrifugation and finally redispersed in hexanes and
1-dodecanethiol (10-20 .mu.L mL.sup.-1 hexanes) with probe
sonication for 1 min.
[0045] For the synthesis of AgNPs, solutions of AgBF4 (40 mM),
1-methylimidazole (1.2 M) and BMIM-BH4 (200 mM) were prepared in
BMIM-Tf2N with stirring at 25.degree. C. Solutions of AgBF4 (0.25
mL) and 1-methylimidazole (0.25 mL) in BMIM-Tf2N were thoroughly
mixed in the absence of light. Thereafter, a solution of BMIM-BH4
in BMIMTf2N (0.5 mL) was rapidly injected resulting in a color
change after ca. 10 s. The AgNPs were isolated by phase transfer
whereby the AgNP dispersion in BMIM-Tf2N was collected into an
organic phase containing hexanes (2 mL), ethanol (2 mL),
1-dodecanethiol (50 .mu.L), and trioctylamine (25 .mu.L). The
colored organic phase containing AgNPs was separated and the AgNPs
precipitated by centrifugation with the addition of methanol (3
mL). The colorless supernatant was replaced with ethanol and the
mixture was sonicated for 2 min using a probe sonicator fitted with
a microtip at 50% duty cycle. The AgNPs were again isolated by
centrifugation and finally redispersed in hexanes (1-2 mL) with
probe sonication for 1 min.
[0046] Characterization.
[0047] TEM was performed on a JEOL JEM-2100 electron microscope at
an operating voltage of 200 kV, equipped with a Gatan Orius CCD
camera. UV-Vis absorption spectra were collected on a Shimadzu
UV-1800 spectrophotometer in dual beam mode using quartz cuvettes
with 1-cm path lengths from nanoparticle dispersions in hexanes.
NMR spectra were collected on a Varian VNMRS-500 2-Channel NMR
spectrometer at 25.degree. C. Viscosity was measured using a
Cannon-Ubbelohde viscometer at room temperature. The /liquid
mixture was composed of the reagent solutions for AuNP synthesis
with the HAuCl.sub.4 solution replaced by pure BMIM-Tf.sub.2N to
prevent gold nanoparticle formation.
[0048] The AuNPs synthesized on device under optimal droplet flow
conditions were spherical and monodisperse with a mean diameter of
4.28.+-.0.84 nm (n=54684), with average major and minor axis
lengths of 4.78 and 4.13 nm, respectively.
[0049] The nanoparticles exhibited an ellipticity of 1.16, defined
as the major axis length/minor axis length. The AuNPs produced in
an analogous batch reaction were larger with a mean diameter of
5.52.+-.0.98 nm (n=57 732) and average major and minor axis lengths
of 6.09 and 5.18 nm, respectively. The AuNPs produced in the batch
reaction possessed an ellipticity of 1.18.
[0050] The end-result AgNPs synthesized on device had a mean
diameter of 3.73.+-.0.77 nm (n=30 249) with major and minor axis
lengths of 4.65 and 3.68 nm, respectively. Striking differences
were observed for AgNPs synthesized in batch. Whereas well-defined
spherical AgNPs were produced on device, the same conditions in
batch produced large coral-like assemblies of very small AgNPs
(<2 nm in diameter).
[0051] The present disclosure can be practiced by employing
conventional materials, methodology and equipment. Accordingly, the
details of such materials, equipment and methodology are not set
forth herein in detail. In the previous descriptions, numerous
specific details are set forth, such as specific materials,
structures, chemicals, processes, etc., in order to provide a
thorough understanding of the disclosure. However, it should be
recognized that the present disclosure can be practiced without
resorting to the details specifically set forth. In other
instances, well known processing structures have not been described
in detail, in order not to unnecessarily obscure the present
disclosure.
[0052] Only a few examples of the present disclosure are shown and
described herein. It is to be understood that the disclosure is
capable of use in various other combinations and environments and
is capable of changes or modifications within the scope of the
inventive concepts as expressed herein.
[0053] The components, steps, features, objects, benefits and
advantages which have been discussed are merely illustrative. None
of them, nor the discussions relating to them, are intended to
limit the scope of protection in any way. Numerous other examples
are also contemplated. These include examples which have fewer,
additional, and/or different components, steps, features, objects,
benefits and advantages. These also include examples in which the
components and/or steps are arranged and/or ordered
differently.
[0054] Unless otherwise stated, all measurements, values, ratings,
positions, magnitudes, sizes, and other specifications which are
set forth in this specification are approximate, not exact. They
are intended to have a reasonable range which is consistent with
the functions to which they relate and with what is customary in
the art to which they pertain.
* * * * *