U.S. patent number 10,907,023 [Application Number 15/990,690] was granted by the patent office on 2021-02-02 for polymer hollow particle, a method of preparing the same, and composite comprising the polymer hollow particle.
This patent grant is currently assigned to KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. The grantee listed for this patent is KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to Kyung Youl Baek, Hyesung Cho, Soon Man Hong, Seung Sang Hwang, Chong Min Koo, Hyunchul Park, Seunggun Yu.
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United States Patent |
10,907,023 |
Koo , et al. |
February 2, 2021 |
Polymer hollow particle, a method of preparing the same, and
composite comprising the polymer hollow particle
Abstract
A method of preparing a polymer hollow particle, a low-specific
gravity and monodispersed polymer hollow particle of various shapes
prepared using the method, and a composite including the polymer
hollow particle are provided. The method includes: a first step of
providing, onto a substrate including a engraved pattern, at least
one expandable particle comprising a foaming agent-containing
expandable core and a thermoplastic polymer shell; a second step of
removing an excess of the at least one expandable particle from a
resulting product of the first step; a third step of expanding the
at least one expandable particle in the engraved pattern of the
substrate by thermally treating a resulting product of the second
step; and a fourth step of separating, from the substrate, expanded
hollow polymer particles which are a resulting product of the third
step.
Inventors: |
Koo; Chong Min (Seoul,
KR), Hong; Soon Man (Seoul, KR), Hwang;
Seung Sang (Seoul, KR), Baek; Kyung Youl (Seoul,
KR), Park; Hyunchul (Seoul, KR), Yu;
Seunggun (Seoul, KR), Cho; Hyesung (Seoul,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY |
Seoul |
N/A |
KR |
|
|
Assignee: |
KOREA INSTITUTE OF SCIENCE AND
TECHNOLOGY (Seoul, KR)
|
Family
ID: |
1000005334907 |
Appl.
No.: |
15/990,690 |
Filed: |
May 28, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190016868 A1 |
Jan 17, 2019 |
|
Foreign Application Priority Data
|
|
|
|
|
Jul 17, 2017 [KR] |
|
|
10-2017-0090379 |
May 4, 2018 [KR] |
|
|
10-2018-0052131 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
13/14 (20130101); C08J 9/32 (20130101); B29C
44/3415 (20130101); C23C 18/1635 (20130101); B29C
44/3461 (20130101); C08J 9/18 (20130101); C08J
9/236 (20130101); C08J 9/228 (20130101); C23C
18/405 (20130101); B29C 44/445 (20130101); C08J
2203/22 (20130101); C08J 2203/14 (20130101); C08J
2363/00 (20130101); C08J 2333/12 (20130101); B29C
2035/0827 (20130101); C08J 9/141 (20130101) |
Current International
Class: |
C08J
9/228 (20060101); C08J 9/18 (20060101); C08J
9/236 (20060101); B29C 44/34 (20060101); C23C
18/40 (20060101); B29C 44/44 (20060101); B01J
13/14 (20060101); C08J 9/32 (20060101); C23C
18/16 (20060101); C08J 9/14 (20060101); B29C
35/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yi; Stella K
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
What is claimed is:
1. A method of preparing polymer hollow particles, the method
comprising: a first step of providing, onto a substrate including
an engraved pattern, at least one expandable particle comprising a
foaming agent-containing expandable core and a thermoplastic
polymer shell; a second step of removing an excess of the at least
one expandable particle from a resulting product of the first step;
a third step of expanding the at least one expandable particle in
the engraved pattern of the substrate by thermally treating a
resulting product of the second step; and a fourth step of
separating, from the substrate, expanded hollow polymer particles
which are a resulting product of the third step, wherein the at
least one expandable particle is provided as monodispersed or
polydispersed particles into the engraved pattern of the substrate
in the first step, and the hollow polymer particles in the fourth
step are monodispersed particles.
2. The method of claim 1, wherein, in the first step, the at least
one expandable particle comprising the expandable core and the
thermoplastic polymer shell is provided with a solvent as a mixture
onto the substrate including the engraved pattern, or is provided
onto the substrate including the engraved pattern in a dry
manner.
3. The method of claim 1, wherein the thermal treating in the third
step is performed at a temperature of about 50.degree. C. to about
170.degree. C.
4. The method of claim 1, wherein the forming foaming agent
comprises a non-fluorine-containing hydrocarbon compound that has a
low boiling point and is present in a gaseous phase at a
temperature equal to or lower than a softening point of a
thermoplastic resin in the thermoplastic polymer shell.
5. The method of claim 1, wherein the thermoplastic resin in the
thermoplastic polymer shell of the at least one expandable particle
comprises a polymer obtained from a polymerizable monomer or a
polymer obtained as a reaction product of a polymerizable monomer
and a cross-linking agent, the polymerizable monomer comprises at
least one selected from the group consisting of a nitrile monomer,
a carboxylic acid monomer, a (meth)acrylic acid ester monomer, an
acrylamide monomer, a maleimide monomer, a vinyl ether monomer, a
vinyl ketone monomer, an aromatic divinyl monomer, a N-vinyl
monomer, a halogenated vinyl monomer, and a combination thereof,
and the cross-linking agent comprises at least one selected from
the group consisting of allyl methacrylate, triacryl formal,
triallyl isocyanate, ethylene glycol di(meth)acrylate, diethylene
glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,
1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate,
1, 10-decanediol di(meth)acrylate, polyethylene glycol
di(meth)acrylate, neopentyl glycoldi(meth)acrylate,
trimethylolpropane trimethacrylate, glycerol dimethacrylate,
dimethylol tricyclodecane diacrylate, pentaerythritol
tri(meth)acrylate, pentaerythritol tetraacrylate, dipentaerythritol
hexaacrylate, neopentyl glycol acrylate benzoate(Neopentylglycol
benzoate acrylate), trimethylol propane acrylate benzoate,
2-hydroxy-3-acryloyloxy propyl methacrylate, hydroxypivalic acid
neopentyl glycol diacrylate, ditrimethylolpropane tetraacrylate,
2-butyl-2-ethyl-1,3-propanediol diacrylate, and a combination
thereof.
6. The method of claim 1, wherein the thermoplastic resin in the
thermoplastic polymer shell of the at least one expandable particle
comprises a terpolymer comprising a (meth)acryl first repeating
unit, a nitrile second repeating unit, and a third repeating unit
having no reactivity with the (meth)acryl first repeating unit and
the nitrile second repeating unit, an amount of the (meth)acryl
first repeating unit is about 10 wt % to about 50 wt %, an amount
of the nitrile second repeating unit is about 30 wt % to about 80
wt %, and an amount of the third repeating unit is about 10 wt % to
about 80 wt %, based on a total weight of the first to third
repeating units in the thermoplastic resin.
7. The method of claim 1, wherein the foaming agent in the
expandable core of the at least one expandable particle comprises
at least one selected from the group consisting of propane,
propylene, butene, normal butane, isobutane, isopentane,
neopentane, normal pentane, normal hexane, isohexane, heptane,
octane, petroleum ether, halogenated methane, tetra alkylsilane,
azodicarbonamide, and a combination thereof.
8. The method of claim 1, wherein the substrate including the
engraved pattern comprises a line or hole pattern, and the hollow
polymer particles each have a line or hole pattern on at least one
surface thereof, according to the line or hole pattern of the
substrate.
9. The method of claim 1, wherein the hollow polymer particles each
have a specific gravity of about 0.001 g/cm.sup.3 to about 1
g/cm.sup.3.
10. The method of claim 1, wherein each of the expanded hollow
polymer particles is in the form of a one-body particle.
11. The method of claim 1, wherein each of the expanded hollow
polymer particles is substantially without grain boundary.
12. The method of claim 1, further comprising surface-treating the
hollow polymer particles to prevent agglomeration or binding
between the particles.
13. The method of claim 1, further comprising surface-treating the
hollow polymer particles with a fluorine material.
14. The method of claim 1, further comprising surface-treating the
hollow polymer particles with 1,1-difluoroethane.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of Korean Patent Application
Nos. 10-2017-0090379, filed on Jul. 17, 2017, and 10-2018-0052131,
filed on May 4, 2018 in the Korean Intellectual Property Office,
the disclosure of which is incorporated herein in its entirety by
reference.
BACKGROUND
1. Field
One or more embodiments relate to polymer hollow particles, a
method of preparing the same, and a composite including the polymer
hollow particles, and more particularly, to a method of preparing
hollow particles using expandable particles, hollow polymer
particles prepared by the method, and a composite including the
polymer hollow particles.
2. Description of the Related Art
Polymer particles are widely used in various fields, for example,
sustained-release formulations, optic materials, chromatography
media, and the like. Recently, research is being performed into
using polymer particles as a building block for preparing a complex
structure. In these fields of application, physical and chemical
properties of polymer particles, including structure, size, shape,
porosity, surface charge, hydrophilicity, and hydrophobicity,
affect function of the particles. Accordingly, it may be crucial to
introduce complexity into a particle structure and to uniformly
control the function. Furthermore, designing polymer particles
having various shapes and various physical and chemical properties
may further expand the fields of application of the polymer
particles.
Known methods of preparing polymer microparticles having a
controlled shape and size include using a microfluidic system,
controlling emulsion polymerization, and phase separation. However,
it is not easy to control density characteristics of particles with
these preparation methods, and the methods themselves are
complicated. Therefore, there is a need for improvement in this
regard.
SUMMARY
One or more embodiments include a method of preparing hollow
polymer particles having various shapes using expandable particles
by heat.
One or more embodiments include a monodispersed polymer hollow
particle having a low specific gravity prepared using the
method.
One or more embodiments include a composite including the polymer
hollow particle.
Additional aspects will be set forth in part in the description
which follows and, in part, will be apparent from the description,
or may be learned by practice of the presented embodiments.
According to one or more embodiments, a method of preparing hollow
polymer particles includes:
a first step of providing, onto a substrate including a engraved
pattern, at least one expandable particle comprising a foaming
agent-containing expandable core and a thermoplastic polymer
shell;
a second step of removing an excess of the at least one expandable
particle from a resulting product of the first step;
a third step of expanding the at least one expandable particle in
the engraved pattern of the substrate by thermally treating a
resulting product of the second step; and
a fourth step of separating, from the substrate, expanded hollow
polymer particles which are a resulting product of the third
step.
In some embodiments, the substrate including the engraved pattern
may have a line or hole pattern, and the polymer hollow particle
may have a line or hole pattern on at least one surface thereof
according to the line or hole pattern of the substrate.
According to one or more embodiments, there is provided a polymer
hollow particle prepared according to the above-described method as
a monodispersed particle comprising the expandable core and the
thermoplastic polymer shell, the polymer hollow particle having a
specific gravity of about 0.001 g/cm.sup.3 to about 1
g/cm.sup.3.
According to one or more embodiments, a composite includes: the
above-described polymer hollow particle; and at least one material
selected from amongan electrically conductive material, an
electromagnetic shielding material, a thermally conductive
material, and a polymer resin.
In some embodiments, the composite may have a structure comprising
the polymer hollow particle; and a coating layer on a surface of
the polymer hollow particle, the coating layer comprising at least
one material selected from amongan electrically conductive
material, an electromagnetic shielding material, a thermally
conductive material, and a polymer resin, or may have a composite
structure comprising the polymer hollow particle; and at least one
material selected from among an electrically conductive material,
an electromagnetic shielding material, a thermally conductive
material, and a polymer resin.
BRIEF DESCRIPTION OF THE DRAWINGS
These and/or other aspects will become apparent and more readily
appreciated from the following description of the embodiments,
taken in conjunction with the accompanying drawings in which:
FIG. 1A is an illustration for explaining a method of preparing
monodispersed hollow polymer particles according to an embodiment
of the inventive concept;
FIG. 1B is an illustration for explaining characteristics of hollow
polymer particles according to embodiments of the inventive
concept;
FIGS. 1C to 1F are optical microscopy images of hollow polymer
particles according to embodiments of the inventive concept;
FIGS. 2A to 2C are optical microscopy images of hollow polymer
particles prepared according to Examples 1, 5, and 6,
respectively;
FIGS. 3A to 3G are optical microscopy images of hollow polymer
particles prepared according to Examples 7 to 13 (8 to 14),
respectively;
FIG. 3H is a magnified image of a region indicated by a rectangle
in FIG. 3G;
FIG. 4A is an optical microscopy image of a polymer hollow particle
prepared according to Example 14; and
FIG. 4B is a magnified image of a region indicated by a rectangle
in FIG. 4A.
DETAILED DESCRIPTION
Reference will now be made in detail to embodiments of polymer
hollows particles, a preparing method thereof, and a composite
including the polymer hollow particles, examples of which are
illustrated in the accompanying drawings, wherein like reference
numerals refer to like elements throughout. In this regard, the
present embodiments may have different forms and should not be
construed as being limited to the descriptions set forth herein.
Accordingly, the embodiments are merely described below, by
referring to the figures, to explain aspects of the present
description. As used herein, the term "and/or" includes any and all
combinations of one or more of the associated listed items.
Expressions such as "at least one of," when preceding a list of
elements, modify the entire list of elements and do not modify the
individual elements of the list.
According to an aspect of the present disclosure, a method of
preparing hollow polymer particles includes:
a first step of providing, onto a substrate including a engraved
pattern, at least one expandable particle comprising a foaming
agent-containing expandable core and a thermoplastic polymer
shell;
a second step of removing an excess of the at least one expandable
particle from a resulting product of the first step;
a third step of expanding the at least one expandable particle in
the engraved pattern of the substrate by thermally treating a
resulting product of the second step; and
a fourth step of separating, from the substrate, expanded hollow
polymer particles which are a resulting product of the third
step.
Using the above-described method, monodispersed hollow polymer
particles having various shapes and a low specific gravity may be
easily prepared using thermally expandable particles.
The number of the at least one expandable particle provided into
the engraved pattern of the substrate may be, whether dispersed or
polydispersed, 1 or greater, for example, in a range of about 1 to
about 1000, 1 to about 500, or 1 to about 100, to control the
density and shape of the resulting expanded, monodispersed polymer
hollow particles. The monodispersed hollow polymer particles as a
target product may be prepared even with polydispersed expandable
particles as a starting material. Such resulting hollow polymer
particles may have a uniform size substantially without
agglomeration of the particles.
As supported by results of diameter distribution analysis by
dynamic light scattering, the hollow polymer particles may be
uniform, monodispersed particles having a uniformly controlled
particle diameter with a degree of dispersion of, for example,
about 5% or less, about 1%, about 0.1% or less, about 0.01% or
less, or about 0.0001 to 0.01%.
In the first step, the at least one expandable particle comprising
the expandable core and the thermoplastic polymer shell may be
provided onto the substrate including a engraved pattern in a wet
manner by being mixed with a solvent. In other embodiments, the at
least one expandable particle comprising the expandable core and
the thermoplastic polymer shell may be provided onto the substrate
in a dry manner, for example, by rubbing or spraying.
In the third step, the thermal treatment may be performed at a
temperature of about 50.degree. C. to about 170.degree. C., for
example, about 90.degree. C. to about 120.degree. C., for example,
at about 100.degree. C. to about 120.degree. C. The thermal
treatment may be performed at a heating rate of about 0.1.degree.
C./min to 20.degree. C./min, for example, about 10.degree. C./min.
When the thermal treatment temperature and the heating rate are
within these ranges, expansion of the expandable particles may be
facilitated, and expanded hollow polymer particles having a desired
polymer shell thickness may be obtained. When the heating rate is
within the above-described ranges, the expandable particle(s) may
remain intact without the occurrence of a structural defect or
damage of the core and shell. As a result, the hollow polymer
particles may have a higher true specific gravity than expected or
may not undergo deterioration in physical properties with respect
to thermal expansion, which may likely occur when the expansion
rate is not controlled as desired.
The substrate including the depressed pattern is for example a mold
having microwells and specific gravity.
When the expandable particle(s) is provided as an aqueous
dispersion onto microwells of a mold (i.e., the substrate including
a engraved pattern), the unnecessary solvent may be removed during
the above-described thermal treatment process. Expansion of the
expandable particle(s) may progress during the thermal treatment
process. For example, the thermal treatment time may be varied
within a range of about 1 second to about 24 hours.
The substrate including a engraved pattern may be manufactured from
a thermocurable silicon polymer, for example, polydimethylsiloxane
(PDMS) by a photoetching process.
After a silicon substrate is coated with a photosensitive resin,
the silicon substrate may be selectively irradiated with
ultraviolet (UV) rays through a photomask having a pattern in a
various shape having a certain width and depth, for example, a
circular, triangular, rectangular, pentagonal, or hexagonal shape,
and then a non-UV irradiated region of the silicon substrate may be
removed using a developing solution, resulting in a mold having a
desired pattern.
PDMS as a thermocurable resin may be applied onto the thus-obtained
mold, cured at a temperature of about 60.degree. C. to 90.degree.
C. for about 10 hours to about 30 hours, and then separated from
the silicon substrate. The resulting product may then be exposed
under oxygen atmosphere to induce formation of a hydrophilic
chemical group on a surface thereof. As a result of the thermal
curing of the PDMS applied flat onto the mold, a PDMS channel
member substrate may be obtained.
The PDMS channel member substrate made flat may be placed onto the
PDMS substrate including a engraved pattern in a various shape and
then integrated together to thereby manufacture a device.
The size of the engraved pattern is not specifically limited. The
size of the engraved pattern may be varied depending on the size of
a target polymer hollow particle. The shape of the expanded polymer
hollow particle may be controlled by controlling the shape of the
engraved pattern in a thickness direction.
With the assumption that the engraved pattern has N sides on a
plane and a side length A, wherein N indicates the number of sides
and A indicates the length of a side, when N is varied within a
range of about 1 to 100 and each side has a same length A, the
engraved pattern may form an expanded polymer hollow particle
having a various isotropic shape from the expandable particle.
With the assumption that the engraved pattern has N sides on a
plane and a side length A, wherein N indicates the number of sides
and A indicates the length of a side, when N is varied within a
range of about 1 to 100 and the length A of each side is not the
same, the engraved pattern may form an expanded polymer hollow
particle having a various anisotropic shape from the expandable
particle.
A width and depth of the engraved pattern are not specifically
limited. For example, the depressed patter may have a width of
about 10 nm to about 1,000 .mu.m and a height of about 10 nm to
about 1,000 .mu.m.
In the middle of the thermal treatment process, an aging process
may be performed for about 1 minute to about 100 minutes. Through
this aging process, the expandable particle may have an increased
expansion ratio, and unnecessary air may be removed.
In some embodiments, in the method of preparing a polymer hollow
particle(s) as described above, the mold may be manufactured to
have a various shape, for example, a circular, square, or
rectangular shape according to a shape of the target polymer hollow
particle(s).
In some embodiments, it may be easy to freely control the shape of
the polymer hollow particle as represented in FIG. 1B (see
Complexity #1 in FIG. 1B and FIG. 1C). In some embodiments, the
edges of the polymer hollow particle may be made round or sharp by
controlling, for example, the thermal treatment temperature (see
Complexity #2 in FIG. 1B and FIG. 1D). As shown in FIG. 1C, the
number of particles constituting one polymer hollow particle may be
controlled as desired. For example, one polymer hollow particle may
include one, two, or three particles (see Complexity #3 in FIG. 1B
and FIG. 1E). For example, one polymer hollow particle may be in
the form of one-body particle, a primary particle, or a secondary
particle. A secondary particle refers to an aggregate of primary
particles. When the polymer hollow particle according to an
embodiment is one-body particle, the polymer hollow particle may
have nearly no grain boundary.
In some embodiments, the hollow polymer particles may be
surface-treated to prevent agglomeration and binding between the
particles. The surface treatment may be coating with, for example,
a fluorine material. For example, the fluorine material may be a
low-molecular weight material such as 1,1-difluoroethane.
In some embodiments, the polymer hollowparticles may have any
desired pattern, for example, holes or lines, on an outer surface
(a upper surface, a lower surface, andor a side thereof) (see
Complexity #4 in FIG. 1B and FIG. 1F).
For example, the amount of the core in the expandable particle may
be about 2 wt % to about 85 wt %, and in some embodiments, about
0.1 wt % to 5.0 wt %, and in some other embodiments, about 1 wt %
to 3 wt %, based on a total weight of the expandable particle. For
example, the amount of the thermoplastic polymer shell may be about
95 wt % to about 99.9 wt % based on the total weight of the
expandable particle. The thermoplastic polymer shell may have a
thickness of about 0.1 .mu.m to about 10 .mu.m.
The expandable particle(s) may have an average particle diameter
of, for example, about 0.2 .mu.m to about 50 .mu.m.
The foaming agent in the at least one expandable particle may
expand the expandable particle to a volume expansion ratio of about
10 times or greater, for example, about 0.01 time to about 10
times, when heated at a temperature greater than or equal to a
softening point of the thermoplastic resin in the polymer
shell.
In some embodiments, the polymer hollow particle may have a large
inner pore, and thus may be used as a mixture with a filler in a
polymer substrate for use as a low-specific gravity structure. When
the polymer hollow particle according to an embodiment is used as a
filler, it may be easy to freely control various characteristics of
a target product, including density, transparency, refractive
index, sound proofing and insulating properties, as desired.
The thermoplastic resin in the thermoplastic polymer shell may be a
polymer obtained from a polymerizable monomer or a polymer obtained
as a reaction product of a polymerizable monomer and a
cross-linking agent. The polymerizable monomer may be at least one
selected from the group consisting of a nitrile monomer, a
carboxylic acid monomer, a (meth)acrylic acid ester monomer, an
acrylamide monomer, a maleimide monomer, a styrene monomer, a vinyl
ether monomer, a vinyl ketone monomer, an aromatic divinyl monomer,
a N-vinyl monomer, a halogenated vinyl monomer, and a combination
thereof.
Non-limiting examples of the nitrile monomer may be acrylonitrile,
methacrylonitrile, a-chloracrylonitrile, a-ethoxyacrylonitrile, and
fumaronitrile. Non-limiting examples of the carboxylic acid monomer
may be a carboxylic acid monomer such as acrylic acid, methacrylic
acid, itaconic acid, maleic acid, fumaric acid, and citraconic
acid; vinylidene chloride, vinyl acetate; methyl(meth)acrylate,
ethyl(meth)acrylate, normal butyl(meth)acrylate,
isobutyl(meth)acrylate, tertiary butyl(meth)acrylate,
isobornyl(meth)acrylate, cyclohexyl(meth)acrylate,
benzyl(meth)acrylate, and carboxyethylene acrylate. Non-limiting
examples of the styrene monomer may be styrene, o-methylstyrene,
m-methylstyrene, p-methylstyrene, p-ethylstyrene,
2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene,
p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene,
p-n-decylstyrene, p-n-dodecylstyrene, n-methoxystyrene,
p-phenylstyrene, p-chlorostyrene, and 3,4-dichlorostyrene.
Non-limiting examples of the acrylamide monomer may be acrylamide,
substituted acrylamide, methacrylamide, and substituted
methacrylamide. Non-limiting examples of the maleimide monomer may
be N-phenyl maleimide, N-(2-chlorophenyl) maleimide, N-cyclohexyl
maleimide, and N-lauryl maleimide.
Non-limiting examples of the vinyl ether monomer may be vinyl
methyl ether, vinyl ethyl ether, and vinyl isobutyl ether.
Non-limiting examples of the vinyl ketone monomer may be vinyl
methyl ketone, vinyl hexyl ketone, and methyl isoprophenyl ketone.
Non-limiting examples of the aromatic divinyl monomer may be
divinyl benzene and divinyl naphthalene. Non-limiting examples of
the (meth)acrylic acid ester monomer may be methyl(meth)acrylate,
ethyl(meth)acrylate, n-butyl (meth)acrylate,
isobutyl(meth)acrylate, t-butyl(meth)acrylate,
propyl(meth)acrylate, n-octyl(meth)acrylate, dodecyl(meth)acrylate,
2-ethylhexyl(meth)acrylate, stearyl(meth)acrylate,
2-chloroethyl(meth)acrylate, phenyl(meth)acrylate,
isobornyl(meth)acrylate, cyclohexyl(meth)acrylate,
benzyl(meth)acrylate, .beta.-carboxyethyl acrylate,
2-hydroxyethyl(meth)acrylate, and 2-hydroxypropyl(meth)acrylate.
Non-limiting examples of the N-vinyl monomer may be N-vinylpyrrole,
N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone.
Non-limiting examples of the halogenated vinyl monomer may be vinyl
chloride, vinylidene chloride, vinyl bromide, and vinyl
fluoride.
The cross-linking agent may be, for example, at least one selected
from the group consisting of allyl methacrylate, triacryl formal,
triallyl isocyanate, ethylene glycol di(meth)acrylate, diethylene
glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,
1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate,
1,10-decanediol di(meth)acrylate, polyethylene glycol
di(meth)acrylate, neopentyl glycoldi(meth)acrylate,
trimethylolpropane trimethacrylate, glycerol dimethacrylate,
dimethylol tricyclodecane diacrylate, pentaerythritol
tri(meth)acrylate, pentaerythritol tetraacrylate, dipentaerythritol
hexaacrylate, neopentyl glycol acrylate benzoate, trimethylol
propane acrylate benzoate, 2-hydroxy-3-acryloyloxy propyl
methacrylate, hydroxypivalic acid neopentyl glycol diacrylate,
ditrimethylolpropane tetraacrylate, 2-butyl-2-ethyl-1,3-propanediol
diacrylate, and a combination thereof. For example, polyethylene
glycol of the polyethylene glycol di(meth)acrylate may have a
weight average molecular weight of about 200, 400, or 600.
The foaming agent in the core of the expandable particle may
include a non-fluorine hydrocarbon compound having a low boiling
point that may be present in a gaseous phase at a temperature equal
to or lower than a softening point of a thermoplastic resin of the
thermoplastic polymer shell.
The foaming agent may maintain an initial decomposition temperature
of, for example, about 150.degree. C. or greater, and may maintain
a maximum degree of expansion at a temperature of about 210.degree.
C. to about 240.degree. C. The core of the expandable particle may
include a foaming agent having a thermal expansion onset
temperature of about -20.degree. C. to about 150.degree. C., for
example, about -15.degree. C. to about 100.degree. C., or about
-12.degree. C. to about 50.degree. C., and a maximum thermal
expansion temperature of about 160.degree. C. to about 170.degree.
C.
The amount of the expandable core may be about 5 wt % to about 30
wt % based on a total weight of of the expandable particle. The
foaming agent may be, for example, at least one selected from among
propane, propylene, butene, normal butane, isobutane, isopentane,
neopentane, normal pentane, normal hexane, isohexane, heptane,
octane, petroleum ether, halogenated methane, tetra alkylsilane,
and azodicarbonamide.
For example, the thermoplastic resin forming the thermoplastic
polymer shell may be a terpolymer including a (meth)acryl first
repeating unit as an essential component, a nitrile second
repeating unit, and a third repeating unit having no reactivity
with the (meth)acryl first repeating unit and the nitrile second
repeating unit.
The thermoplastic resin may include the first repeating unit and
the second repeating unit in any a certain ratio. In some
embodiments, the amount of the (meth)acryl first repeating unit may
be about 10 wt % to about 50 wt %, for example about 15 wt % to
about 30 wt % based on a total weight of the thermoplastic resin.
The amount of the nitrile second repeating unit may be about 30 wt
% to about 80 wt %, for example, about 35 wt % to about 50 wt %,
based on based on a total weight of the first to third repeating
units in the thermoplastic resin.
The third repeating unit may be, for example, at least one selected
from among polyvinylchloride, N-methylol(meth)acrylamide,
N,N-dimethylaminoethyl(meth)acrylate,
N,N-dimethylaminopropyl(meth)acrylate, magnesiummono(meth)acrylate,
zinc mono(meth)acrylate, vinylglycidylether,
prophenylglycidylether, glycidyl(meth)acrylate,
2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,
2-hydroxybutyl(meth)acrylate, and
2-hydroxy-3-phenoxypropyl(meth)acrylate.
The thermoplastic resin may include the first repeating unit, the
second repeating unit, and the third repeating unit in any a
certain ratio. The amount of the third repeating unit may be about
10 wt % to about 50 wt %, for example, about 35 wt % to about 45 wt
%, based on a total weight of the thermoplastic resin.
The thermoplastic resin may be, for example, a
vinylchloride-co-acrylonitrile-co-methyl methacrylate copolymer.
The amount of the acrylonitrile repeating unit may be about 10 wt %
to about 50 wt %, the amount of the methyl methacrylate repeating
unit may be about 30 wt % to about 80 wt %, and the amount of the
vinyl chloride repeating unit may be about 10 wt % to about 50 wt
%, (each based on a total weight of the thermoplastic resin.)
When using the expandable particle including a polymer shell having
the above-described composition, the resulting polymer hollow
particle after expansion may have a desired polymer shell
thickness. After completion of the expansion, the expandable
particle may remain intact without structural defect or damage of
the core and shell, and the polymer hollow particle may have an
improved specific gravity and improved thermal expansion
property.
Hereinafter, embodiments of a method of preparing hollow polymer
particles according to any of the embodiments will be described in
greater detail.
At least one expandable particle including a foaming
agent-containing expandable core and a thermoplastic polymer shell
may be provided into microwells of a mold as a substrate including
a engraved pattern. The at least one expandable particle may be
provided in the form of powder without a solvent onto the substrate
in a dry manner, for example, by rubbing or spraying into the
microwells.
Even when the expandable particle provided into the microwells is a
polydispersed particle, the resulting final polymer hollow particle
may be a monodispersed particle having a high degree of
dispersion.
When hollow polymer particles according to embodiments are prepared
using a wet process, it may be essential to use a mold cover and
dock the particles and evaporate a solvent used in dispersion of
the particles in the microwells of the mold. It may also be
essential to precisely control the affinity and surface energy of
the solvent to the mold used in the wet process. In addition, for
mass-scale production of the polymer hollow particles, it may be
essential to uniformly control the evaporation of the solvent.
Preparing hollow polymer particles according to an embodiment using
a wet process will now be described in greater detail.
In a method of preparing hollow polymer particles using a wet
process, at least one expandable particle may be provided onto a
substrate in the same manner as in a dry method, except that the
expandable particle is provided into the microwells of the
substrate in the form of an expandable particle dispersion in a
solvent, instead of powder form.
The solvent may be, for example, water. The amount of the solvent
may be about 1 part to about 99 parts by weight based on 100 parts
by weight of the expendable particle.
A PDMS channel member substrate may be placed onto a
polydimethylsiloxane (PDMS) substrate including a engraved pattern
and then integrated together to thereby manufacture a device. The
expandable particle-containing dispersion may be supplied to the
microwells of the PDMS substrate (mold) having the engraved pattern
through the channels in the PDMS channel member substrate.
The mold may be a soft mold using a polymer such as polyurethane or
polydimethylsiloxane, or may be a hard mold such as a metal mold.
The soft mold may be easily manufactured from a silicon master mold
through a simple duplication process.
Preparing hollow polymer particles using a dry process may be
simpler and easier than the above-described wet preparation process
since the additional process and equipment required in the wet
process are not needed. Using such a dry process may be
advantageous since a PDMS channel member substrate used in the wet
process to supply the expandable particle-containing dispersion is
not required.
In the dry preparation process, after the spraying of the
expandable particles into the microwells, a taping process using an
adhesive tape, a blowing process, or a process of applying
ultrasonic waves may be performed. The taping process is for
removing the remaining expandable particles using tape. The excess
expandable particles remaining in the microwells may be removed
through the blowing process or the process of applying ultrasonic
waves. The taping process may more effectively remove an excess of
the expandable particles than the blowing process and the process
of applying ultrasonic waves.
Through the above-described taping process, blowing process, or
process of applying ultrasonic waves, the expandable particles may
be appropriately supplied into the microwells of the mold so that
desired hollow polymer particles are obtained.
After the at least one expandable particle is supplied into the
microwells of the mold in a wet or dry manner as described above,
thermal treatment may be performed. The thermal treatment may be
performed in a range of temperatures higher than a glass transition
temperature of the thermoplastic resin which forms the shell of the
expandable particle.
The resulting product from the first step may be thermally treated
to expand the expandable particle supplied into the engraved
pattern (of the substrate).
A polymer hollow particle completely expanded resulting from the
second step, may then be separated from the substrate. In other
words, after being completely expanded in the mold, the polymer
hollow particle may be separated from the mold. The polymer hollow
particle may be separated from the mold by using transonic waves, a
water-soluble tape or blowing.
In the method of preparing polymer hollow particles, according to
an embodiment, hollow polymer particles may be obtained in the form
of one-body particles, primary particles or secondary particles
according to a thermal treatment temperature, thermal treatment
time, or whether surface treatment has been performed or not.
The hollow polymer particles may have a coating layer on a surface
thereof formed by surface treatment with a fluorine material. The
hollow polymer particles obtained through such surface treatment
may be one-body particles substantially without grain boundary due
to suppressed agglomeration and binding of the particles. For
example, the fluorine material may be a low-molecular weight
material such as 1,1-difluoroethane.
According to another aspect of the present disclosure, there are
provided hollow polymer particles prepared using a method according
to an embodiment as described above, as monodispersed particles
including an expandable core and a thermoplastic polymer shell as
described above and having a specific density of about 0.001
g/cm.sup.3 to about 1 g/cm.sup.3 and a degree of dispersion of
about 5% or less.
In some embodiments, hollow polymer particles having various shapes
may be prepared through low-temperature heating and a short
process. In some embodiments, edges of the hollow polymer particles
may be precisely controlled by changing temperature and expansion
pressure conditions. It may also be possible to control the density
of the hollow polymer particles by varying the number of particles
or degree of expansion. A pattern of high precision may be
implemented with high expansion pressure.
According to another aspect of the present disclosure, a composite
includes a polymer hollow particle according to any of the
above-described embodiments.
The composite may include a polymer hollow particle according to
any of the above-described embodiments and at least one material
selected from among an electrically conductive material, an
electromagnetic shielding material, a thermal conductive material,
and a polymer resin. The polymer resin is a thermoplastic resin or
a thermocurable resin.
In some embodiments, the at least one material selected from among
a conductive material, an electromagnetic shielding material, a
thermal conductive material, a thermoplastic resin and a
thermocurable resin may be included in the coating layer on the
surface of the polymer hollow particle. In some other embodiments,
the at least one material selected from among a conductive
material, an electromagnetic shielding material, a thermal
conductive material, a thermoplastic resin and a thermocurable
resin may form a composite with the polymer hollow particle.
In some embodiments, the composite may be used as a filler. The
composite may have a particle size of, for example, about 100 nm to
about 100,000 nm. The size of the composite may refer to an average
particle diameter when the composite is spherical, or may refer to
a length of the major axis when the composite is nonspherical.
As described above, The composite may include a polymer hollow
particle according to any of the embodiments and at least one
material selected from among a conductive material, an
electromagnetic shielding material, a thermal conductive material,
a thermoplastic resin, and a thermocurable resin.
For example, the at least one material may be at least one selected
from the group consisting of Al, Ag, Au, Cu, Ni, Sn, Pt, Si, Ge,
In, Sb, Pb, Bi, Cd, Zn, Mo, W, Ti and a combination thereof. For
example, the at least one material may be at least one selected
from CuO, Cu.sub.2O, SiO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, CaO,
B.sub.2O.sub.3, B.sub.2O, B.sub.6O, Al.sub.2O.sub.3, BeO, ZnO, MgO,
SiC, AlN, SiN, BN, BCN, titanium carbide (Ti.sub.xC.sub.y),
titanium nitride (Ti.sub.xN.sub.y), titanium carbonitride
(Ti.sub.xC.sub.yN.sub.z), carbon nanotubes (CNT), graphite,
graphene, diamond, fullerene, carbon black, and a combination
thereof.
The thermoplastic resin and the thermocurable resin may be any ones
widely known in the art.
The composite may be prepared to have a various particle shape,
structure, and composition. Accordingly, the density, electrical
conductivity, electromagnetic shielding characteristics, and
thermal conductive characteristics of the composite may be
efficiently controlled. The low density, large surface area, and
surface characteristics of the composite may be controlled, so that
the composite may be useful in a biomaterial, a chemical material,
a fusion material, and a constructive material.
When hollow polymer particles according to any of the
above-described embodiments or a composite including the polymer
hollow material are applied to a biomaterial, functional particles
for an effective drug delivery and release system may not be
limited to spherical particles but may be prepared in the form of
anisotropic particles or hollow particles. When hollow polymer
particles according to any of the above-described embodiments or a
composite including the polymer hollow material are applied to a
construction material, a construction and exterior materials of
lighter weight may be easily obtained by being filled with the
polymer hollow particle or a composite including the same, beyond
the limit to which spherical particles may be packed(beyond the
limitation of spherical particles in closest packing).
When hollow polymer particles according to any of the
above-described embodiments or a composite including the polymer
hollow material are applied to a photonic crystalline material, a
novel photonic crystalline structure which has not previously
existed may be implemented with anisotropic particles according to
embodiments, and a next-generation photoelectric device may be
manufactured using the photonic crystalline structure. Hollow
polymer particles according to any of the embodiments and a
composite including the same are nanoparticles which may be
applicable to a variety of fields, including optic materials,
intelligent drug delivery and release systems, small electronic
circuits, biosensors, and catalyst supports.
One or more embodiments of the present disclosure will now be
described in detail with reference to the following examples.
However, these examples are only for illustrative purposes and are
not intended to limit the scope of the one or more embodiments of
the present disclosure.
Example 1
Preparation of Polymer Hollow Particle
A substrate including a engraved pattern(referred to also as a mold
having a pattern or microwells) was manufactured using
poly(dimethylsiloxane) (PDMS) known as a thermocurable silicon
polymer using a photoetching process.
First, after a silicon substrate was coated with a photosensitive
resin and then selectively irradiated with ultraviolet (UV) rays
through a photomask, a non-UV irradiated region of the silicon
substrate was removed using a developing solution to obtain a mold
having a desired pattern.
The thermocurable polymer PDMS was then coated on the obtained
mold, cured at a temperature of about 80.degree. C. for about 24
hours, and then separated from the silicon substrate, thereby
manufacturing a PDMS substrate A including a engraved pattern.
A PDMS channel member substrate with channels was mounted on the
PDMS substrate A including a engraved pattern and then integrated
together to thereby manufacture a device. An expandable
particle-containing dispersion prepared as described below was then
supplied through the channels of the PDMS channel member substrate
into the microwells of the PDMS substrate A (mold). The PDMS
channel member substrate was treated with oxygen plasma for about 1
minute to induce hydroxyl groups as hydrophilic chemical groups on
a surface of the PDMS channel substrate, so as to facilitate smooth
and uniform supply of the expandable particle-containing dispersion
into the microwells of the PDMS substrate A through the channels of
the PDMS channel member substrate.
The expandable particle-containing dispersion was prepared by
dispersing two expandable particles (461 DU, SEKISUI) having a
diameter of about 10 .mu.m in water. The amount of the expandable
particles in the expandable particle-containing dispersion was
about 1 wt %.
The expandable particles used were in the form of powder including
an isobutane core and a vinylidene
chloride-co-acrylonitrile-co-methyl methacrylate copolymer shell.
The vinylidene chloride-co-acrylonitrile-co-methyl methacrylate
copolymer included vinylidene chloride, acrylonitrile and methyl
methacrylate repeating units in a weight ratio of about
25:35:40.
After the supplying of the expandable particle-containing
dispersion, the PDMS channel member substrate was separated from
the resulting product (the PDMS substrate A) and then a
channel-free flat PDMS substrate (referred also as a mold cover)
was bound to the PDMS substrate A. The resulting product was then
placed into a hot stage and then heated to about 100.degree. C. at
a rate of about 10.degree. C./min to expand the expandable
particles, thereby preparing expanded polymer hollow particles.
Next, the channel-free flat PDMS substrate (mold cover) was
separated from the device including the expanded hollow polymer
particles prepared through the above-described processes.
The expanded hollow polymer particles in the engraved pattern of
the PDMSsubstrate A were separated from the PDMS substrate A using
a water-soluble adhesive tape (available from Clover Mfg Co., Ltd),
which was attached to an upper surface of the PDMS substrate and
gently detached therefrom. Next, the water-soluble adhesive tape
with the expanded hollow polymer particles attached thereto was
dissolved in water to isolate the expanded hollow polymer particles
from the same, thereby obtaining target monodispersed hollow
polymer particles having a rectangular shape.
Example 2
0.1 g of expandable particles were placed into the microwells
(having a depth of about 20 .mu.m and a width of about 20 .mu.m) of
the PDMS substrate A (mold) obtained according to Example 1, and
then rubbed with a planar PDMS block in one direction to be filled
into the microwells of the mold. Next, a common 3M Scotch tape was
attached to an upper surface of the mold with the microwells filled
with the expandable particles and then detached therefrom to remove
an excess of the expandable particles. These processes were
repeated three times until the mold was filled with a minimum
amount of the expandable particles sufficient to shape the
particles.
The expandable particles used were in the form of powder including
an isobutane core and a vinylidene
chloride-co-acrylonitrile-co-methyl methacrylate copolymer shell.
The vinylidene chloride-co-acrylonitrile-co-methyl methacrylate
copolymer included vinylidene chloride, acrylonitrile and methyl
methacrylate repeating units in a weight ratio of about
25:35:40.
The resulting product obtained through the above processes was
bound with a channel-free flat PDMS substrate (referred also as a
mold cover). The resulting product was then placed into a hot stage
and then heated to about 100.degree. C. at a rate of about
10.degree. C./min to expand the expandable particles, thereby
preparing expanded polymer hollow particles.
The expanded hollow polymer particles in the engraved pattern of
the PDMS substrate were separated from the PDMS substrate A using a
water-soluble adhesive tape (available from Clover Mfg Co., Ltd),
which was attached to an upper surface of the PDMS substrate and
gently detached therefrom. Next, the water-soluble adhesive tape
with the expanded hollow polymer particles attached thereto was
dissolved in water to isolate the expanded hollow polymer particles
from the same, thereby obtaining target monodispersed hollow
polymer particles having a rectangular shape.
Example 3
Preparation of Polymer Hollow Particle/Epoxy Resin Composite
A room temperature-curable epoxy resin and a curing agent were
mixed in an equivalence ratio. After the resulting mixture was
poured into a mold prepared according to Example 1, the mold
containing the resulting mixture was placed into a Revolution
centrifugal mixer and spun at about 1000 rpm for about 5 minutes,
thereby preparing an epoxy mixture(epoxy melt) as a uniform mixture
of the epoxy resin and the curing agent.
After 10 g of the hollow polymer particles prepared according to
Example 1 was mixed with 10 g of theepoxy mixture(epoxy melt), the
mixture was further mixed in a Revolution centrifugal mixer at
about 1000 rpm for about 5 minutes, thereby preparing a polymer
hollow particle/epoxy resin composite.
Example 4
Preparation of Polymer Hollow Particle/Epoxy Resin Composite
10 g of the hollow polymer particles prepared according to Example
1 were treated with an acid to remove impurities from the surfaces
thereof, thereby preparing first polymer hollow particles.
After an electroless copper solution including 7 mL of an aqueous
solution of copper sulfate (CuSO.sub.4.5H.sub.2O) as a copper salt,
0.7 mL of formaldehyde (HCHO) as a reducing agent, and 2.8 g of
ethylene diamine tetraacetic acid (C.sub.10H.sub.16N.sub.2O.sub.8)
as a complexing agent was prepared, the first hollow polymer
particles were dipped in the electroless copper solution for about
120 minutes and stirred to prepare hollow polymer particles having
a copper coating layer.
A mixture of an epoxy resin and a curing agent in a calculated
equivalence ratio was poured into a mold. This mold was then placed
into a Revolution centrifugal mixer and spun at about 1000 rpm for
about 5 minutes, thereby preparing an epoxy mixture(epoxy melt) as
a uniform mixture of the epoxy resin and the curing agent.
10 mL of the hollow polymer particles having the copper coating
layer was mixed with 10 g of theepoxy mixture(epoxy melt), and then
further mixed in a Revolution centrifugal mixer at about 1000 rpm
for about 5 minutes, thereby preparing a polymer hollow
particle/epoxy resin composite.
Example 5
Hollow polymer particles having a spherical shape were prepared in
the same manner as in Example 1, except that a device obtained by
integrating the PDMS substrate A including a engraved pattern with
a channel-free flat PDMS substrate according to Example 1 was
placed into a hot stage and then heated to about 90.degree. C.,
instead of 100.degree. C., at a rate of about 20.degree.
C./min.
Example 6
Hollow polymer particles having a triangular shape with sharp edges
were prepared by expanding expandable particles in the same manner
as in Example 1, except that a device obtained by integrating the
PDMS substrate A including a engraved pattern with a channel-free
flat PDMS substrate according to Example 1 was placed into a hot
stage and then heated to about 110.degree. C., instead of
100.degree. C., at a rate of about 20 C/min.
Example 7
Hollow polymer particles were prepared in the same manner as in
Example 1, except that the channel-free flat PDMS substrate (mold
cover) was modified to have a nano line pattern (having a line
width of about 600 nm), the microwells of the PDMS substrate A
including a engraved pattern had a circular shape, and one
expandable particle was placed in each of the microwells.
Example 8
Hollow polymer particles were prepared in the same manner as in
Example 7, except that two expandable particles were placed in each
of the microwells of the PDMS substrate A including a engraved
pattern.
Example 9
Hollow polymer particles were prepared in the same manner as in
Example 1, except that the channel-free flat PDMS substrate (mold
cover) was modified to have a nano line pattern, and one expandable
particle was placed in each of the microwells of the PDMS substrate
A including a engraved pattern.
Example 10
Hollow polymer particles were prepared in the same manner as in
Example 9, except that two expandable particles were placed in each
of the microwells the PDMS substrate A including a engraved
pattern.
Example 11
Hollow polymer particles were prepared in the same manner as in
Example 1, except that the channel-free flat PDMS substrate (mold
cover) was modified to have a nano line pattern, the microwells of
the PDMS substrate A including a engraved pattern had a rectangular
shape, and one expandable particle was placed in each of the
microwells.
Example 12
Hollow polymer particles were prepared in the same manner as in
Example 11, except that two expandable particles were placed in
each of the microwells of the PDMS substrate A including a engraved
pattern.
Example 13
Hollow polymer particles were prepared in the same manner as in
Example 1, except that the channel-free flat PDMS substrate (mold
cover) was modified to have a nano line pattern, the microwells of
the PDMS substrate (PDMS substrate A) including a engraved pattern
had a pentagonal shape, and one expandable particle was placed in
(each of) the microwells.
Example 14
Hollow polymer particles were prepared in the same manner as in
Example 1, except that the channel-free flat PDMS substrate (mold
cover) or the mold was modified to have a nano hole pattern (having
a hole diameter of about 600 nm), and two expandable particles were
placed in each of the microwells of the PDMS substrate A including
a engraved pattern.
Examples 15-16
Hollow polymer particles were prepared in the same manner as in
Example 1, except that a device resulting from integrating the PDMS
substrate A including a engraved pattern with a channel-free flat
PDMS was placed into a hot stage and then heated to about
100.degree. C. at a rate of about 0.1.degree. C./min and 20.degree.
C./min, respectively, to expand the expandable particles and thus
obtain expanded hollow polymer particles.
Examples 17-18
Hollow polymer particles were prepared in the same manner as in
Example 2, except that a device resulting from integrating the PDMS
substrate A including a engraved pattern with a channel-free flat
PDMS substrate was placed into a hot stage and then heated to about
100.degree. C. at a rate of about 0.1.degree. C./min and 20.degree.
C./min, respectively, to expand the expandable particles and thus
obtain expanded hollow polymer particles.
Comparative Example 1
10 mL of polystylene particles (having a diameter of about 40 um)
were mixed with 10 mL of the epoxy mixture(epoxy melt) prepared in
Example 3, and then further mixed in a Revolution centrifugal mixer
at about 1000 rpm for about 5 minutes, thereby preparing a polymer
particle/epoxy resin composite.
Comparative Example 2
To compare the amount of copper present on the surface of the
hollow polymer particles of Example 4 with that on the surface of
common polymer particles, 0.1 mL of common copper particles (having
a diameter of about 10 um) equivalent to the amount of copper
present on the surface of the hollow polymer particles coated with
copper according to Example 4 were mixed with 10 mL of theepoxy
mixture(epoxy melt), and then further mixed in a Revolution
centrifugal mixer at about 1000 rpm for about 5 minutes, thereby
preparing a polymer particle/epoxy resin composite.
Comparative Example 3
Nanoparticles were prepared using a duplicated mold with microwells
having a triangular cross-section having a depth of about 50 .mu.m
and a side length of about 150 .mu.m. After the microwells of the
duplicated mold were filled with polyethylene glycol diacrylate
(PEG-DA, Mw=575, available from Sigma-Aldrich Chemicals), the
filled mold was left in a vacuum chamber for about 5 minutes to
remove air bubbles from the microwells. An excess of PEG-DA flowing
over the microwells was recovered by tilting the duplicated mold or
by utilizing capillary force with a pipette tip so that PEG-DA was
filled just to the rims of the microwells. Next, while a solvent
including about 1 to 5 vol % of 2,2-diethoxyacetophenone (DEAP) as
a photoinitiator was applied to cover the upper surface of the
microwells, the upper surface of the microwells was imaged with a
Nikon TE2000 inverted microscope (TE2000, Nikon, Japan) equipped
with a CCD camera (Coolsnap, Photometrics, USA) to observe changes
with time. After 20 minutes from the applying of the solvent, the
microwells of the duplicated mold were irradiated with ultraviolet
(UV) rays of 365 nm using a 8-W small UV lamp (Spectronics Corp.,
Westbury, N.Y.) for about 2 minutes. After the UV irradiation, the
duplicated mold was dipped in IPA (isopropyl alcohol (IPA) to
recover polymer microparticles. The solvent used was PDMS oil (Dow
Corning) or Fluorinert.RTM. FC-40 (available from Sigma).
Evaluation Example 1
Specific Gravity
Specific gravities of the composites prepared according to Example
3 and Comparative Example 1 were measured based on an apparent
specific gravity determination method. The results are shown in
Table 1.
TABLE-US-00001 TABLE 1 Example 3 Comparative Example 1 Specific
gravity (g/cm.sup.3) 0.08 1.10
Referring to Table 1, the composite of Example 3 including the
hollow polymer particles having pores was found to have a
significantly reduced specific gravity, compared to the composite
of Comparative Example 1.
Referring to Table 1, the composite of Example 3 including the
hollow polymer particles having pores was found to have a
significantly reduced specific gravity, compared to the composite
of Comparative Example 1.
Evaluation Example 2
Electrical Conductivity and Thermal Conductivity
Electrical conductivity and thermal conductivity of the composite
of Example 4 were compared with those of the composite of
Comparative Example 2.
After the composites of Example 4 and Comparative Example 2 were
processed to have a thickness of about 2 mm, electrical
conductivity and thermal diffusivity thereof were determined based
on the methods according to ASTM F 390 and ASTM E 1461-92,
respectively. The thermal diffusivity was converted into electrical
conductivity by multiplying density by specific heat. The resulting
electrical conductivity and thermal conductivity values are shown
in Table 2.
TABLE-US-00002 TABLE 2 Example 4 Comparative Example 2 Electrical
conductivity (S/cm) 6.0 .times. 10.sup.2 1.0 .times. 10.sup.-6
Thermal conductivity (W/mK) 4.0 0.5
Referring to Table 2, the polymer hollow particle/epoxy resin
composite prepared in Example 4 coated with copper was found to
have remarkably improved electrical conductivity and thermal
conductivity compared to the copper-coated polymer particle/epoxy
resin composite prepared in Comparative Example 2, due to an
efficient conduction effect of the copper-coated electrical and
thermal conduction paths.
Evaluation Example 3
Optical Microscopy
1) Examples 1, 5-6
The hollow polymer particles prepared according to Examples 1, 5,
and 6 were analyzed using an optical microscope. The analysis
results are shown in FIGS. 2A to 2C. The optical microscope used
was a Leica DM2500 (available from Leica Microsystems)
When the expandable particles in the microwells were heated to
about 90.degree. C., unexpanded microparticles were observed as
shown in FIG. 2A. Referring to FIG. 2A, when the expanded particles
in the microwells were heated to about 100.degree. C.,
microparticles having round edges were observed.
When the expandable particles in the microwells were heated to
about 110.degree. C., microbombs having sharp edges were observed.
When the expandable particles in the microwells were heated to
about 120.degree. C., microbombs having a rupture structure were
observed. There results indicate that the shape of hollow polymer
particles may be controlled according to a heat treatment
temperature of the expendable particles.
As described above, the shape of the hollow polymer particles may
be easily controlled to have round or sharp edges by varying the
heat treatment temperature as in Example 1 and Examples 5-7. When
an edge shape of target particles is controlled by controlling the
shape of a mold as in Comparative Example 3, preparation costs may
be increased and the shape of feasible target particles may also be
limited.
2) Examples 8-14
The hollow polymer particles prepared according to Examples 8-14
were observed by optical microscopy.
The optical microscopy images of the hollow polymer particles of
Examples 8-14 are shown in FIGS. 3A to 3H. FIG. 3H is a magnified
image of a region delimited by a rectangle in FIG. 3G.
Referring to FIGS. 3A to 3H, the polymer hollows particles of
Examples 7-13 were found to have an imprinted linear nanopattern on
the surfaces thereof when the nanopattern of the microwells of the
mold and the nanopattern of the mold cover were formed as a nano
line pattern.
3) Example 14
The hollow polymer particles prepared according to Example 14 were
observed by optical microscopy.
The optical microscopy images of the hollow polymer particles of
Example 14 are shown in FIGS. 4A and 4B. FIG. 4B is a magnified
image of a region delimited by a rectangle in FIG. 4A.
Referring to FIGS. 4A and 4B, the hollow polymer particles of
Example 14 were found to have an imprinted nanopattern of holes on
the surfaces thereof when the nanopattern of the microwells of the
mold and the nanopattern of the mold cover were formed as a hole
pattern.
Evaluation Example 4
Observation of Limited Expansion Behavior
To observe limited expansion behavior of the hollow polymer
particles prepared in Example 1, the expansion behavior of the
hollow polymer particles was tracked in real time during the
preparation process.
According to a result of the observation, the shape of the final
polymer hollow particle was determined according to the pattern
shape of the microwells of the mold, and the expansion ratio of
individual polymer hole particles was increased with time.
Evaluation Example 5
Particle Size Distribution Characteristic
Particle size distribution characteristics of the hollow polymer
particles prepared according to Examples 1 and 2 and the polymer
particles prepared according to Comparative Example 3 were
evaluated.
According to a result of the evaluation, the hollow polymer
particles of Examples 1 and 2 were found to be monodispersed
particles having a uniform particle size, while the polymer
particles of Comparative Example 3 were found to be polydispersed
particles having different particle sizes, unlike the hollow
polymer particles of Examples 1 and 2.
Particle size distribution characteristics of the hollow polymer
particles prepared according to Examples 15 to 18 were also
evaluated. As a result, the hollow polymer particles of Examples 15
to 18 were also found to be monodispersed particles having a
uniform particle size, like the hollow polymer particles of
Examples 1 and 2.
As described above, according to the one or more embodiments,
hollow polymer particles having different shapes may be prepared
using thermally expandable particles. The shape of the hollow
polymer particles may be easy controlled according to a pattern
shape of a mold as the expandable particles applied into the
pattern of the mold are heated to expand to fit to the shape of the
pattern, and the hollow polymer particles may have a low specific
gravity.
It should be understood that embodiments described herein should be
considered in a descriptive sense only and not for purposes of
limitation. Descriptions of features or aspects within each
embodiment should typically be considered as available for other
similar features or aspects in other embodiments.
While one or more embodiments have been described with reference to
the figures, it will be understood by those of ordinary skill in
the art that various changes in form and details may be made
therein without departing from the spirit and scope of the
inventive concept as defined by the following claims.
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