U.S. patent application number 12/572726 was filed with the patent office on 2011-04-07 for polymer-encapsulated nanoparticle systems.
Invention is credited to Doris Pik-Yiu Chun, Hou T. Ng.
Application Number | 20110079756 12/572726 |
Document ID | / |
Family ID | 43822491 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110079756 |
Kind Code |
A1 |
Chun; Doris Pik-Yiu ; et
al. |
April 7, 2011 |
POLYMER-ENCAPSULATED NANOPARTICLE SYSTEMS
Abstract
A polymer-encapsulated nanoparticle system includes a
non-aqueous medium; and polymer-encapsulated nanoparticles formed
in situ in the non-aqueous medium. Each polymer-encapsulated
particle has a diameter that is less than 1 micron, and includes a
solid particle core, and a polymer coating established directly on
the solid particle core.
Inventors: |
Chun; Doris Pik-Yiu; (Santa
Clara, CA) ; Ng; Hou T.; (Palo Alto, CA) |
Family ID: |
43822491 |
Appl. No.: |
12/572726 |
Filed: |
October 2, 2009 |
Current U.S.
Class: |
252/572 |
Current CPC
Class: |
C08C 19/22 20130101;
C08C 19/24 20130101; C08C 19/25 20130101; B05D 7/00 20130101; C08F
220/56 20130101; C08C 19/20 20130101 |
Class at
Publication: |
252/572 |
International
Class: |
H01B 3/20 20060101
H01B003/20 |
Claims
1. A polymer-encapsulated nanoparticle system, comprising: a
non-aqueous medium; and polymer-encapsulated nanoparticles formed
in situ in the non-aqueous medium, each polymer-encapsulated
particle having a diameter that is less than 1 micron and
including: a solid particle core; and a polymer coating established
directly on the solid particle core.
2. The polymer-encapsulated nanoparticle system as defined in claim
1 wherein the non-aqueous medium is a dielectric material, and
wherein the polymer coating of the polymer-encapsulated
nanoparticles further includes an ionic species configured to
promote charging of the polymer coating.
3. The polymer-encapsulated nanoparticle system as defined in claim
2 wherein the ionic species is an aliphatic acid salt of a chain
aliphatic derivative containing one of acids and bases, wherein the
chain aliphatic derivative includes at least 5 carbon atoms, and
wherein the acids are selected from oleic, valeric, hexanoic,
heptanoic, caprylic, nonanoic, capric, lauric, myristic, palmitic,
heptadecanoic, stearic, arachidic, behenic, lignoceri, sulfuric,
phosphoric, boronic, sulfonic, sulfamic, nitric, nitrous,
nitrosulfuric, and pyrophosphoric acids, or wherein the bases are
selected from primary, secondary, tertiary, quaternary, and
aromatic amines.
4. The polymer-encapsulated nanoparticle system as defined in claim
1 wherein the non-aqueous medium is a non-oxidative water
immiscible medium.
5. A field responsive system, comprising: a non-aqueous dielectric
medium; polymer-encapsulated nanoparticles formed in situ in and
dispersed in the non-aqueous dielectric medium, each
polymer-encapsulated particle having a diameter that is less than 1
micron and including: a solid particle core; and a polymer coating
established directly on the solid particle core, the polymer
coating including an ionic species which imparts a reversible
charge to each polymer-encapsulated nanoparticle; and a source of
an electric field configured to charge the polymer-encapsulated
nanoparticles in a predetermined manner.
6. A method for forming a system including polymer-encapsulated
nanoparticles, the method comprising: forming an inverse
mini-emulsion including a continuous phase of a non-aqueous medium
and a discontinuous phase of at least: a plurality of nanoparticles
having a polar surface, and at least one of i) a polar,
water-soluble, or water-miscible monomer, or ii) a polar,
water-soluble, or water-miscible pre-polymer; and initiating
polymerization of the at least one of the monomer or the prepolymer
to form a polymer coating on each of the plurality of nanoparticles
in the non-aqueous medium.
7. The method as defined in claim 6 wherein the forming of the
inverse mini-emulsion is accomplished in the absence of water.
8. The method as defined in claim 6 wherein the at least one of i)
the polar, water-soluble, or water-miscible monomer, or ii) the
polar, water-soluble, or water-miscible pre-polymer is a solid, and
wherein prior to forming the inverse mini-emulsion, the method
further comprises: dissolving the at least one of i) the polar,
water-soluble, or water-miscible monomer, or ii) the polar,
water-soluble, or water-miscible pre-polymer; and adding the
plurality of nanoparticles to the aqueous solvent.
9. The method as defined in claim 6 wherein forming the inverse
mini-emulsion includes: mechanically mixing the plurality of
nanoparticles, a radical initiator, and the at least one i) the
polar, water-soluble, or water-miscible monomer, or ii) the polar,
water-soluble, or water-miscible pre-polymer, thereby forming a
mixture; adding a surfactant or dispersant dissolved in the
non-aqueous medium to the mixture; subjecting the mixture to mixing
at a rate greater than or equal to 0.5 k rpm to form a suspension;
and microhomogenizing the suspension at a predetermined pressure
for a predetermined number of cycles.
10. The method as defined in claim 9 wherein microhomogenizing
includes exposing the suspension to a pressurized chamber, wherein
the predetermined pressure is up to 33,000 psi, and wherein the
predetermined number of cycles ranges from 1 to 6, where each cycle
is 5 minutes at 250 mL/min.
11. The method as defined in claim 9, further comprising adding a
charge generating component during the mechanically mixing
step.
12. The method as defined in claim 11 wherein the charge generating
component is an aliphatic acid salt of a chain aliphatic derivative
containing one of acids and bases, wherein the chain aliphatic
derivative includes at least 5 carbon atoms, and wherein the acids
are selected from oleic, valeric, hexanoic, heptanoic, caprylic,
nonanoic, capric, lauric, myristic, palmitic, heptadecanoic,
stearic, arachidic, behenic, lignoceri, sulfuric, phosphoric,
boronic, sulfonic, sulfamic, nitric, nitrous, nitrosulfuric, and
pyrophosphoric acids, or wherein the bases are selected from
primary, secondary, tertiary, quaternary, and aromatic amines.
13. The method as defined in claim 9 wherein an amount of the
surfactant ranges from about 0.01 wt % to about 40 wt % of a total
weight of the surfactant or dispersant dissolved in the non-aqueous
medium.
14. The method as defined in claim 6, further comprising selecting
the plurality of nanoparticles from the group consisting of carbon
black, copper phthalocyanine, titania, and silica.
15. The method as defined in claim 6 wherein initiating
polymerization of the inverse mini-emulsion is accomplished at a
predetermined temperature.
16. The method as defined in claim 15, further comprising including
a crosslinker and an initiator in the discontinuous phase.
17. The method as defined in claim 6, further comprising including
a charge generating component in the discontinuous phase.
18. The method as defined in claim 6, further comprising including
at least one of a surfactant, a dispersant, a crosslinker, an
initiator, a rheology modifier, and an acid-group containing
monomer in the discontinuous phase.
19. The method as defined in claim 6, further comprising adding a
polar, water-soluble, or water-miscible polymer to the
discontinuous phase.
20. The method as defined in claim 6 wherein each
polymer-encapsulated particle has a diameter that is less than 1
micron.
Description
BACKGROUND
[0001] The present disclosure relates generally to
polymer-encapsulated nanoparticle systems.
[0002] Encapsulated particles have become increasingly useful in a
variety of biological applications (e.g., drugs, cosmetics, etc.),
printing applications (e.g., laser printing, digital commercial
printing, etc.), and electronic applications (e.g., electronic
inks, light emitting polymers, e-field displays, etc.). The
production of such particles often involves multiple steps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] Features and advantages of embodiments of the present
disclosure will become apparent by reference to the following
detailed description and drawing, in which like reference numerals
correspond to similar, though not necessarily identical,
components. For the sake of brevity, reference numerals or features
having a previously described function may or may not be described
in connection with other drawings in which they appear.
[0004] FIGS. 1A and 1B together schematically illustrate an
embodiment of a method for forming embodiments of the
polymer-encapsulated nanoparticles;
[0005] FIG. 2 is a flow diagram illustrating more detailed
embodiments of the method for forming embodiments of the
polymer-encapsulated nanoparticles; and
[0006] FIGS. 3A through 3C are photographs of electrodes coated
with polymer-encapsulated nanoparticles when a voltage is applied
to only the even-numbered electrode (FIG. 3A), the voltage is
removed from the even-numbered electrodes and applied to the
odd-numbered electrodes (FIG. 3B), and to only the odd-numbered
electrodes (FIG. 3C).
DETAILED DESCRIPTION
[0007] Steps of embodiments of the method disclosed herein may
advantageously be performed in a single container. The continuous
processes enable polymer-coated/encapsulated particles to form in
situ, directly in a desirable non-aqueous medium. This
advantageously eliminates the need to perform a post-polymerization
step to remove water in exchange for the non-aqueous medium. As
such, the methods disclosed herein may be relatively
cost-effective, energy-efficient, waste-efficient, and
time-efficient (especially when compared to processes requiring the
removal of water). Furthermore, in some embodiments, the process
may be configured to generate polymer-encapsulated nanoparticles
that are reversibly chargeable in the presence of an electric
field.
[0008] FIGS. 1A and 1B respectively depict schematic illustrations
of an inverse mini-emulsion (which is a direct emulsion of an
aqueous phase in a non-aqueous phase), and polymer-encapsulated
nanoparticles in a non-aqueous medium formed after in situ
polymerization of the inverse mini-emulsion. FIG. 2 illustrates
embodiments of the method of forming the inverse emulsion, and
forming polymer-encapsulated nanoparticles in a non-aqueous medium
from the inverse emulsion. The various Figures will be referenced
throughout the following description.
[0009] The mini-emulsion 10 shown in FIG. 1A includes a continuous
phase C and a discontinuous phase D. In the embodiments disclosed
herein, the continuous phase C generally includes a non-aqueous
medium 12, and the discontinuous phase includes one or more
hydrophilic components (discussed further hereinbelow). As such,
the mini-emulsion 10 is comparable to a water-in-oil emulsion.
Formation of the mini-emulsion 10 will be discussed herein in
reference to FIGS. 2 and 1A together.
[0010] As shown in FIG. 2 at reference numeral 200 (alone or in
combination with the step shown at reference numeral 202), the
method begins by mixing the components that will ultimately form
the discontinuous phase D. As shown schematically in FIG. 1A, the
discontinuous phase D may include many different components. As
non-limiting examples, the discontinuous phase D includes at least
a plurality of nanoparticles 14 having a polar surface (or surface
modified to achieve a polar surface) and i) polar, water-miscible,
and/or water soluble monomer(s) 16 and/or ii) polar,
water-miscible, and/or water soluble pre-polymer(s) 20.
Furthermore, in some instances, it may be desirable to add one or
more polar, water-soluble, or water-miscible polymers 18 with the
monomers 16 and/or pre-polymers 20. While all of the monomers 16,
polymers 18, and pre-polymers 20 are shown in the discontinuous
phase D in FIG. 1A, it is to be understood that one or any
combination of such materials 16, 18, 20 may be included in the
discontinuous phase D. As such, very generally, the method begins
by mixing the nanoparticles 14 with the monomer(s) 16 and/or
pre-polymer(s) 20 (with or without polymer(s) 16) to form a
mixture. Such mixing may be accomplished mechanically.
[0011] Numerous examples of the nanoparticles 14 and the monomers
16, polymers 18 and pre-polymers 20 are provided hereinbelow.
However, it is to be understood that any suitable starting
materials (e.g., 14, 16, 18, 20) may be selected for the
discontinuous phase D as long as the selected components satisfy
surface compatibility (i.e., the surface of such components are
chemically compatible (e.g., all surfaces are polar)) and are able
to emulsify in the continuous phase C. This enables one to select
from a wide variety of materials, and to tailor the resulting
system 100 (shown in FIG. 1B) for a particular application.
Examples of suitable nanoparticles 14 (which ultimately form the
solid particle core 14' of the encapsulated nanoparticles 22)
include, but are not limited to, colorants (e.g., organic pigments,
inorganic pigments, or dyes), quantum dots, or metal colloids. Such
nanoparticles 14 inherently have a polar surface, or are modified
to have a polar surface. When it is desirable to modify the
polarity of the nanoparticle 14 surface, surfactants are added to
the mixture. More specific non-limiting examples of the
nanoparticles 14 include carbon black, copper phthalocyanine,
titania, and silica. The particle 14 loading in the mixture
generally ranges from about 3 wt % to about 10 wt % of the total
weight of the mixture.
[0012] The initial size (i.e., diameter) of the nanoparticles 14
may range from about 0.2 microns to about 5 microns, depending upon
the material selected. It is to be understood that the particle
core 14' of the encapsulated particle 22 (shown in FIG. 1B) size
depends, at least in part, on the extent of homogenization
(discussed further hereinbelow). The size of the encapsulated
particle 22 is generally less than 1 micron, and thus the particle
core 14' is also smaller than 1 micron. It is to be understood that
monomers 16, polymers 18, and/or pre-polymers 20 may be used, and
that such monomers 16, polymers 18, and/or pre-polymers 20 are
polar, water-soluble, and/or water-miscible. Examples of suitable
monomers 16 include, but are not limited to, radical polymerizable
acrylic monomers such as acrylic acid, methacrylic acid,
acrylamide, methacrylamide, hydroxyethyl-methacrylate (HEMA), and
any ethylene-oxide-base methacrylate. Furthermore, examples of
suitable polymers 18 include, but are not limited to polyethylene
glycol methacrylate (PEGMA) or any polymer that is to be formed
from the polymerization of the selected monomer(s) 16 and/or
pre-polymer(s) 20. Still further, examples of suitable pre-polymers
20 include TDI-polyether pre-polymers (e.g., a non-limiting example
of which includes VERSATHANE.RTM. 1090, which is commercially
available from Air Products, Allentown, Pa.), or polyethylene-oxide
based MDI pre-polymers with a viscosity less than 1000 cP (e.g.,
non-limiting examples of which include the DESMODUR.RTM. VP.PU
series, which are commercially available from Bayer Corp.,
Pittsburgh, Pa.).
[0013] When monomer(s) 16 (with or without polymer(s) 18) are used
in the mixture that will form the discontinuous phase D, it is
desirable to include an initiator (e.g.,
2,2'-Azobis(2-methylpropionamidine) dihydrochloride,
4,4'-Azobis(4-cyanovaleric acid), or the like), and when
pre-polymers 20 are used in the mixture that will form the
discontinuous phase D, it is desirable to include water-soluble
cross-linker(s) (e.g., any diamine, such as VERSALINK.RTM. from Air
Products, Allentown, Pa., and JEFFAMINE.RTM. D230 from Huntsman
International, LLC, The Woodlands, Tex.).
[0014] Still other components that may be present in the mixture
that will form the discontinuous phase D include acid-containing
monomers (e.g., acrylates of itaconic acid, maleic acid, vinyl
benzoic acid, or derivatives thereof, or combinations thereof),
rheology modifier(s) (e.g., aqueous modifiers including alkylene
oxides, such as polypropylene glycols, tetraethylene glycol ether,
and diethylene glycol), dispersant(s), co-surfactant(s) (e.g.,
sodium dodecyl sulfate (SDS), DOWFAX.RTM. 2A1 and 30599 (available
from The Dow Chemical Co., Midland, Mich.), the EFKA series
(available from Ciba Specialty Chemical Inc., Switzerland)), and/or
charge generating agents. The loading of such additional components
depends, at least in part on the desirable properties of the
discontinuous phase D. As one example, the rheology modifier may be
added in an amount ranging from about 0.5 wt % to about 30 wt %,
depending upon the desirable viscosity.
[0015] The addition of the charge generating agents to the mixture
(making up the discontinuous phase D) is shown at reference numeral
202 in FIG. 2. It is to be understood that the charge generating
agents are generally an ionic species, such as aliphatic acid salts
of a medium or long chain aliphatic derivative containing acids or
bases. Generally, the aliphatic derivative includes at least 5
carbon atoms. Examples of suitable organic acids that may be part
of the aliphatic derivative include oleic, valeric, hexanoic,
heptanoic, caprylic, nonanoic, capric, lauric, myristic, palmitic,
heptadecanoic, stearic, arachidic, behenic, and lignoceri acids;
and examples of suitable inorganic acids that may be part of the
aliphatic derivative includes sulfuric, phosphoric, boronic,
sulfonic, sulfamic, nitric, nitrous, nitrosulfuric, and
pyrophosphoric acids. Examples of suitable bases that may be part
of the aliphatic derivative include primary, secondary, tertiary,
quaternary, and aromatic amines. Other suitable charge generating
agents include ionic surfactants or dispersants. The selection of
the charge generating agent is dependent upon the nature of
materials being used. For example, in order to disperse hydrophobic
particles in water, sodium dodecylsulfate,
alkyl-phenyl-disulfonate, laureth sulfate, or AEROSOL.RTM. OT can
be used.
[0016] The selected ionic species promote charging of the resulting
polymer-encapsulated particles 22. As such, when the charge
generating agent is included, electric field chargeable
polymer-encapsulated nanoparticles 22 are formed directly in the
non-aqueous solvent medium 12. Such electric field chargeable
polymer-encapsulated nanoparticles 22 can be charged and physically
manipulated to move in an appropriate dielectric medium. This
particular system (i.e., the system including the chargeable
polymer-encapsulated nanoparticles 22) may be particularly suitable
for any device that operates based on the electrophoretic movement
of particles, including, but not limited to, electrophoretic
displays and liquid electrophotography.
[0017] The desirable charges may be formed in situ. For example, if
the surface of the nanoparticle 14, such as pigments, is acidic
(having carboxylic acid groups on the surface) the addition of an
amine functional dispersant will form a conjugate acid/base, giving
rise to charge formation. As such, if the nanoparticle 14 surface
is acidic or basic, the nanoparticle 14 itself can generate the
desirable charge when subjected to base or acid, respectively.
[0018] It is to be further understood that in mixing the components
that will form the discontinuous phase D, water or another solvent
may be used to get the solid components into solution. When water
is not selected to assist in the dissolution of components for the
discontinuous phase D, the formation of the emulsion 10 is
accomplished without using any water.
[0019] Again referring to FIG. 2, the method continues with mixing
together the components that will ultimately form the continuous
phase C of the mini-emulsion 10. This is shown at reference numeral
204 of FIG. 2. In particular, a non-aqueous medium 12 is mixed with
a surfactant and/or dispersant. The resulting medium 12 has the
surfactant and/or dispersant dissolved therein.
[0020] The non-aqueous medium 12 may be selected from any non-water
based solvent in which it is desirable to form the
polymer-encapsulated nanoparticles 22. Non-limiting examples of
such non-aqueous media include dielectric media, non-oxidative
water immiscible media (e.g., petroleum distillates), or other
organic solvent media. In one non-limiting example, the non-aqueous
media is an isoparaffinic hydrocarbon (such as those in the
ISOPAR.RTM. series available from Exxon Mobile Corp., Houston,
Tex.). In other non-limiting examples, the non-aqueous media
includes linear, branched, or cyclic hydrocarbons (such as
n-hexanes, heptanes, octane, cyclohexane, dodecane) or mixtures
thereof, soy bean oil, vegetable oil, or plant extracts. It is to
be understood that when it is desirable to form electric field
responsive particles, the medium 12 selected is capable of enabling
the movement of such field responsive particles, and is often a
dielectric medium.
[0021] As previously mentioned, mixed with the non-aqueous medium
12 is a surfactant and/or dispersant. Surfactants are surface
active agents, which are generally small molecules (i.e.,
m.w.<1000 amu) that lower the surface energy of materials.
Dispersants can serve the function of a surfactant, but are
typically higher in molecular weight (m.w.>2000 amu) and are
able to stabilize particles in the continuous phase C. For the
non-aqueous continuous phase C disclosed herein, a suitable
surfactant includes a sulfosuccinate, such as
bis-(2-ethylhexyl)-sulfosuccinate (AOT). As non-limiting examples,
the dispersant may be selected from a 100% active polymeric
dispersant (e.g., SOLSPERSE.RTM. 19000, commercially available from
Lubrizol Corp., Wickliffe, Ohio), a solution of a 40% active
polymeric dispersant in 240/260 (.degree. C.) aliphatic distillate
(e.g., SOLSPERSE.RTM. 13940, commercially available from Lubrizol
Corp., Wickliffe, Ohio), or other hyperdispersants, such as
SOLSPERSE.RTM. 11000, 17000, 21000, and 2155 (from Lubrizol Corp.,
Wickliffe, Ohio).
[0022] It is to be understood that the type and/or loading of the
surfactant and/or dispersant affects the size of the resulting
polymer-encapsulated nanoparticles 22 (shown in FIG. 1B). More
particularly, the surfactant loading affects the size of the
encapsulated particles 22, and the surfactant and dispersant
together affect the dispersion stability of the final system 100.
If the loading of the surfactant is increased, the particle 14 size
will decrease. Depending upon the surfactant selected (governed, at
least in part, by the critical micelle concentration (CMC)), the
loading will vary. For example, SDS may be used in an amount that
is less than 20 wt % of the pigment (i.e., nanoparticle 14)
loading, and the average encapsulated particles 22 size is 250 nm.
A loading of less than 20 wt % will result in larger encapsulated
particles, up to microns in size. Determining the amount of
surfactant and/or dispersant will depend upon, at least in part,
the combination of materials used, the surface area of the
nanoparticles 14 used in the discontinuous phase D, and the
desirable size of the nanoparticle cores 14' after being dispersed.
In one embodiment, the total amount of surfactant and/or dispersant
ranges from about 0.01 wt % to about 40 wt % of the total weight of
the materials used to form the continuous phase C. In a
non-limiting example, the total amount of surfactant and/or
dispersant ranges from about 0.5 wt % to about 10 wt %.
[0023] The continuous phase C may also include additional non-polar
additives, such as rheology modifiers. Such non-polar modifiers
include oil soluble amine and acid polymers and oligomers.
Non-limiting examples include SOLSPERSE.RTM. 3000 and 21000
(Lubrizol Corp., Wickliffe, Ohio). The loading of the modifier
depends, at least in part, on the application and the desirable
viscosity. In one embodiment, the non-polar modifier is present in
an amount ranging from about 0.5 wt % to about 30 wt % of the total
weight of the continuous phase.
[0024] As shown in FIG. 2 at reference numeral 206, the mixture and
the non-aqueous medium 12 are mixed together (e.g., in a container
24 shown in FIG. 1A). In one embodiment, the mixture is present in
the container 24, and then the surfactant/dispersant dissolved in
the non-aqueous medium 12 is added thereto. In another embodiment,
the surfactant/dispersant dissolved in the non-aqueous medium 12 is
present in the container 24, and then the mixture is added
thereto.
[0025] The combination of the mixture and the non-aqueous medium 12
is then subjected to high-speed mixing to form a suspension, as
shown at reference numeral 208 in FIG. 2. The high-speed mixing is
accomplished at a rate greater than or equal to 0.5 krpm for a time
sufficient to disperse a majority of the nanoparticles 14, thereby
forming nanoparticle cores 14'. In one embodiment, the mixing time
ranges from about 0.01 hours to about 10 hours.
[0026] The suspension is then microhomogenized to form the inverse
mini-emulsion 10 (see reference numeral 210 in FIG. 2 and FIG. 1A).
In one embodiment, the container 24 containing the suspension is
transferred to a microfluidizer where it is subjected to a
predetermined pressure for a predetermined number of cycles or is
microfluidized for a particular amount of time. In one embodiment,
the shearing pressure is up to 33,000 psi inside the reaction
chamber (or higher if the equipment used enables such higher
pressures), and the number of cycles ranges from 1 to 6 (where a
single cycle is about 5 minutes long at 250 mL/min). In one
non-limiting example, the microfluidizer operates at about 240
mL/min. For a 480 mL sample using this microfluidizer, a single
cycle may be as low as 2 minutes long. As such, the cycle time may
change depending, at least in part, on the microfluidizer used and
the sample size. Generally, an under homogenized emulsion will not
be stable, and the particle size and size distribution will
increase. However, an over homogenized emulsion may lead to
separation of the nanoparticles 14 from the monomers 16 or
pre-polymers 20. It is believed that if the operation pressure is
tuned and controlled throughout the process, over homogenization
may be avoided. As such, longer exposure to homogenization
generally leads to a more stable and finer emulsion.
[0027] It is to be understood that the arrangement of an auxiliary
process module (APM) and interaction chamber, which are components
of a microfluidizer, used in the process may also affect the size
of the suspension. Generally, the size (i.e., diameter) of the
interaction chamber may range from 50 .mu.m to 400 .mu.m. In one
embodiment, the microfluidizer used has an 87 micron diameter. The
interaction chamber diameter affects the size of the emulsion that
is prepared, at least in part because a smaller chamber diameter
generates higher operational pressure and thus smaller particle
sizes. While a microfluidizer is mentioned herein, it is to be
understood that any other microhomogenizer may be used to emulsify
the components.
[0028] It is believed that the conditions and parameters used
during microhomogenizing may be controlled to further reduce the
size of the nanoparticles 14 such that desirable nanoparticle cores
14' result. In particular, by controlling the pressure and the
number of cycles to which the suspension is exposed, the particles
14 may be reduced such that the diameter of each particle core 14'
(in the resulting encapsulated particles 22) is less than 500 nm.
As one example, the shearing force increases with the amount of
pressure applied.
[0029] After microhomogenization, the resulting homogeneously mixed
suspension is a stable emulsion of the discontinuous phase D in the
continuous phase C (as shown in FIG. 1A). It is to be understood
that the phases are enlarged in FIG. 1A, and that the discontinuous
phase D may be in the form of droplets in the continuous phase C.
In one embodiment, the discontinuous phase D droplets are less than
1 .mu.m, and in another embodiment, the discontinuous phase D
droplets are less than 500 nm. The emulsion 10 is collected and
then exposed to further conditions to generate the
polymer-encapsulated nanoparticles 22. Formation of such
polymer-encapsulated nanoparticles 22 in the non-aqueous medium 12
from the mini-emulsion 10 will be discussed herein in reference to
FIGS. 2 and 1B together.
[0030] The emulsion 10 (e.g., still contained in container 24) may
be transferred into a reaction vessel (not shown). Polymerization
of at least some of the components of the discontinuous phase D is
then initiated (see reference numeral 212 of FIG. 2). Initiation of
polymerization may be accomplished thermally. It is to be
understood that the temperature at which polymerization initiation
takes place will depend, at least in part, upon the initiation
temperature of the initiator or cross-linker used in the
discontinuous phase D. In a non-limiting example, such thermal
initiation takes place at a temperature ranging from about
75.degree. C. to about 85.degree. C. The emulsion 10 may be exposed
to such temperatures for a time sufficient to complete
polymerization (or cross-linking if polymers 18 are part of the
starting mixture) and form the coating 26 on the nanoparticle core
14'. In a non-limiting example, the thermal initiation is
accomplished for a time ranging from about 0.01 hours to about 10
hours.
[0031] Prior to polymerization, the reactor may be purged under a
stream of an inert gas. This is accomplished, at least in part,
because radicals are susceptible to oxidation by molecular oxygen.
Purging the reaction vessel can help displace some oxygen to
prevent extensive quenching of radicals generated from the
initiator. Furthermore, the reactor may be equipped with a water
condenser, which helps to reintroduce the evaporated continuous
phase C back into the reaction vessel.
[0032] The resulting system 100 is shown schematically in FIG. 1B.
The system 100 includes the encapsulated particles 22 formed
directly in the desired non-aqueous medium 12. The
polymer-encapsulated nanoparticles 22 include the nanoparticle core
14' and the polymer coating 26 established therein. Since the
particles 22 are formed in situ, additional water removal or
solvent exchange steps are not required.
[0033] The resulting coating 26 may, in some embodiments, be
covalently bonded to the nanoparticle core 14' if there are
olefinic double bonds on the particle 14 surface to react with
added monomers 16. Otherwise, the coating 26 is non-covalently
bonded, and is held to the surface of the particle core 14'
initially by non-bonding interactions such as van der Waals forces,
hydrogen bonding, acid/base interaction, and Zwitterionic
interactions. Once polymerization begins, and cross-linking of the
resulting polymers takes place, the polymers are physically
entangled with the surface of the nanoparticle cores 14'.
[0034] As mentioned hereinabove, when a charge controlling agent is
incorporated into the discontinuous phase D, the resulting coating
26 may be charged in the presence of an electric field. Upon
exposure of the particles 22 to such a field, the particles 22 may
be moved in a predetermined manner. Such chargeable particles 22
may be particularly suitable for display and other electronic
applications.
[0035] It is to be understood that the embodiments of the method
disclosed herein may be performed as a one container process (i.e.,
the formation of the emulsion 10 and polymerization thereof occurs
in the same container).
[0036] To further illustrate embodiment(s) of the present
disclosure, the following examples are given herein. It is to be
understood that these examples are provided for illustrative
purposes and are not to be construed as limiting the scope of the
disclosed embodiment(s).
Example 1
[0037] A 1 L Erlenmeyer flask was charged with 10 mL diethylene
glycol and 10 mL water. 1 g of 2,2'-Azobis(2-methylpropionamidine)
dihydrochloride and 40 g of acrylamide were added to the flask. The
solvent and water were used to dissolve the solid acrylamide.
Subsequently, 30 g of Heubach 515400 pigments were stirred into the
glycol solution to form a pasty solid. 1 L of ISOPAR.RTM. L
containing 2 wt % SOLSPERSE.RTM. 19000 was added to the pigment
paste. The heterogeneous mixture underwent primary dispersion by
mechanical stirring at 1000 rpm for 30 minutes under a stream of
argon, and then was further dispersed by microfluidization in a
MICROFLUIDIZER.RTM. (model 110-Y with an 87 micron interaction
chamber) at 60 to 80 applied psi (an internal shear pressure of
approximately 20 kpsi). The solution cycled through 3 times, and
was then collected into a reactor equipped with 2 impellers, a
stirring mechanism, a condenser, and purged with argon for 5
minutes prior to the thermally initiated polymerization at
80.degree. C. The reaction proceeded for 8 hours under argon. Upon
completion of reaction, the dispersion was allowed to cool to room
temperature. The dispersion was screened through a 10 micron
aluminum screen to remove larger particulates to give an oil-based
dispersion of encapsulated nanoparticles.
Example 2
[0038] 1 g of 4,4'-Azobis(4-cyanovaleric acid), 2 g of aluminum
stearate (as a charge controlling agent), and 40 mL of methacrylic
acid were added to a 1 L Erlenmeyer flask. Subsequently, 20 g of
Clariant B-PFS pigments were stirred into the monomer mixture to
form a pasty solid. 1 L of ISOPAR.RTM. containing 2.5 wt %
SOLSPERSE.RTM. 13940 was added the pigment paste. The heterogeneous
mixture underwent primary dispersion by mechanical stirring at 1000
rpm for 30 minutes under a stream of argon, and then was further
dispersed by microfluidization in a MICROFLUIDIZER.RTM. (model
110-Y with an 87 micron interaction chamber) at 60 to 80 applied
psi (an internal shear pressure of approximately 20 kpsi). The
solution cycled through 3 times, and was then collected into a
reactor equipped with 2 impellers, a stirring mechanism, a
condenser, and purged with argon for 5 minute prior to the
thermally initiated polymerization at 80.degree. C. The reaction
proceeded for 8 hours under argon. Upon completion of reaction, the
dispersion was allowed to cool to room temperature. The dispersion
was screened through a 10 micron aluminum screen to remove larger
particulates to give an oil-based dispersion of encapsulated
nanoparticles.
Example 3
[0039] A 1 L Erlenmeyer flask was charged with 10 mL of
toluene-diisocyanate and 40 g of Versathane 1090.25 g of Degussa
Printex 25 was stirred into this viscous mixture to form a pasty
solid. 1 L of ISOPAR.RTM. containing 2.5 wt % SOLSPERSE.RTM. 13940
was added to the pigment paste. The heterogeneous mixture underwent
primary dispersion by mechanical stirring at 1000 rpm for 30
minutes under a stream of argon, and then was further dispersed by
microfluidization in a MICROFLUIDIZER.RTM. (model 110-Y with an 87
micron interaction chamber) at 60 to 80 applied psi (an internal
shear pressure of approximately 20 kpsi). The solution cycled
through 3 times, and then was collected into a reactor equipped
with 2 impellers, a stirring mechanism, a condenser, and purged
with argon for 5 minute prior to the thermally initiated
polymerization at 80.degree. C. The reaction proceeded for 8 hours
under argon. Upon completion of reaction, the dispersion was
allowed to cool to room temperature. The dispersion was screened
through a 10 micron aluminum screen to remove larger particulates
to give an oil-based dispersion of encapsulated nanoparticles.
Example 4
[0040] The particles from Example 1, Example 2, or Example 3 are
incubated in ISOPAR.RTM. L with additional dispersants (e.g., from
5 wt % to 20 wt % of a combination of a SOLSPERSE.RTM.
hyperdispersant and a dispersant available from Chevron Oronite) as
charge generating agents. This dispersion is loaded into an
in-plane Gordon cell (similar to that shown in FIGS. 3A through
3C). It is to be understood that the electrodes of the in-plane
Gordon cell in these Figures are numbered from 1-10. As shown in
these Figures, the encapsulated particles (the black speckles)
migrate from one electrode to another, depending upon the voltages
that are applied and removed. As a particular electric field is
applied, the particles are coated onto certain electrodes via
electrophoretic movements. FIG. 3A illustrates particle movement
when 20V is applied to the even-numbered electrodes of the cell. As
shown, the encapsulated particles migrate towards those electrodes.
FIG. 3B illustrates particle movement when the voltage from the
even-numbered electrodes is removed and the same voltage is applied
to the odd-numbered electrodes. As illustrated, the coated
particles begin to move toward the odd-numbered electrodes and away
from the even-numbered electrodes. FIG. 3C illustrates the complete
switch of the particles from concentrating at the even-numbered
electrodes (FIG. 3A) to concentrating at the odd-numbered
electrodes.
[0041] While several embodiments have been described in detail, it
will be apparent to those skilled in the art that the disclosed
embodiments may be modified. Therefore, the foregoing description
is to be considered exemplary rather than limiting.
* * * * *