Preparation of core-shell organic-inorganic nanocomposite particles based on phase separation of a polymer blend

Article abstract of DOI:10.1246/cl.2009.964

Polymer nanoparticles with phase-separation structures can be prepared by simple solvent evaporation process from block copolymer or polymer blend solution (self-organized precipitation (SORP)). In this report, core-shell organic-inorganic nanocomposite p

Full text of DOI:10.1246/cl.2009.964

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Chemistry Letters Vol.38, No.10 (2009)
Preparation of Core–Shell Organic–Inorganic Nanocomposite Particles
Based on Phase Separation of a Polymer Blend
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Hiroshi Yabu,
Kazutaka Koike, Kiwamu Motoyoshi, Takeshi Higuchi, and Masatsugu Shimomura
Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University,
-1-1 Katahira, Aoba-ku, Sendai 980-8577
Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST),
Sanbancho, Chiyoda-ku, Tokyo 102-0075
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Graduate School of Engineering, Tohoku University, 6-6 Aramaki-Aza, Sendai 980-8579
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WPI-Advanced Institute for Materials Research (AIMR), Tohoku University,
2-1-1 Katahira, Aoba-ku, Sendai 980-8577
(Received July 27, 2009; CL-090700; E-mail: yabu@tagen.tohoku.ac.jp)
Polymer nanoparticles with phase-separation structures can
be prepared by simple solvent evaporation process from block
copolymer or polymer blend solution (self-organized precipita-
tion (SORP)). In this report, core–shell organic–inorganic nano-
composite particles were prepared by combination of block co-
polymer stabilizing Au nanoparticles and polymer blend. Block
copolymer stabilizing Au NPs were prepared by reduction of Au
ion in their micelles. Nanocomposite particles of poly(methyl
methacrylate) (PMMA) and block copolymer stabilizing Au
NPs are successfully prepared by using the SORP method.
Nanostructured polymer particles received great interest due
to their potentials for various applications in the photonics, elec-
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tronics, and biotechnologies. There are several methods for pre-
paring nanostructured polymer particles including seed polymer-
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ization, emulsion polymerization by using microfluidic chan-
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nels, and precipitation. We have reported that phase-separated
polymer particles can be prepared by evaporating good solvent
from the solution of block copolymers or polymer blends con-
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taining poor solvent. Unique nanostructured polymer particles
including one-dimensionally stacked lamellae, onion, Janus,
and core–shell structures have been prepared by using this sim-
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ple evaporation method.
Figure 1. A schematic illustration of the core–shell nanocom-
posite particles.
Metal–polymer nanocomposite materials are also key mate-
rials in the nanotechnology. By using high conductivity, reflec-
tivity, and mechanical stability of metals, polymer materials
are functionalized with nanoscale hybridization of metals. Metal
nanoparticles (NPs) show unique optical and electronic proper-
the SORP method. Control of inner structures of Au NPs–poly-
mer composite particles is discussed.
Figure 1 shows a schematic illustration of preparation of Au
NPs and composite particles. Poly(styrene-block-2-vinylpyri-
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ties based on their quantum and plasmonic effects. Especially,
Au NPs show local plasmonic absorption in the visible light
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dine) (PS-b-P2VP, MnðPSÞ ¼ 17:5 kg mol , MnðP2VPÞ ¼ 9:5
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wavelength region depending on their sizes and shapes. The ar-
kg mol , Mw=Mn ¼ 1:10), PMMA (Mn ¼ 15:8 kg mol , Mw=
Mn ¼ 1:06) were purchased from Polymer Source Inc., USA.
rangement and spacing between the Au NPs strongly affect the
plasmonic absorption. Thus, control of arrangement of particles
is important to realize their unique optical properties.
.
Hydrogen tetrachloroaurate (III) tetrahydrate (HAuCl4 4H2O)
and hydrazine hydrate were purchased from Wako Chemical
Industry, Japan. Dehydrated toluene and tetrahydrofran (THF)
were also purchased from Wako Chemical Industry, Japan and
used without further purification.
In many methods forpreparing Au NPs, reduction of Au ionin
the block copolymer micelles is a simple way to obtain size-con-
trolled Au NPs stabilized with polymers. Spatz et al. reported that
poly(styrene-block-4-vinylpyridine) forms micelles in their tol-
uene solution, and several metal particles were prepared by simple
Au NPs embedded in the block copolymer micelles were
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prepared according to the literature. PS-b-P2VP (5 mg mL )
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reduction of metal ions complexed with pyridine moieties. By
and HAuCl4 4H2O (mol equivalent to 0.5 pyridine unit) were
dissolved in toluene. The solution was degassed in a three-neck
glass flask equipped with nitrogen inlet, vacuum pump, and seal-
ing septum by three cycles of pump–thaw–evacuate. After de-
gassing, the atmosphere was filled with dry nitrogen.
using this method, polymer stabilizing Au NPs can be prepared.
In this report, we show the preparation of Au NPs stabilized
by block copolymers and preparation of Au NPs and polymer
composite particles with phase-separation structures by using
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.10 (2009)
965
Figure 3. A SEM mode (a), a dark field STEM mode (b) image,
and a cross-sectional TEM image (c) of a core–shell type nano-
composite particle.
In a previous report,11 we found that the phase-separation
structures in the polymer blend particles were governed by hy-
drophobicity of the blended polymers. During the formation
process of the particles, the water content of solution increased
with evaporation of THF. As a result, hydrophilic PMMA do-
main encapsulated the hydrophobic PS-b-P2VP stabilizing Au
NPs as protective colloids.
We have shown that core–shell nanocomposite particles can
be formed by using the SORP method. This method can be ap-
plicable to form various kinds of metal particles and polymer
blend systems. Moreover, these nanocomposite particles with
unique phase-separation structures can be applicable to a wide
variety of applications in the fields of electronics, photonics,
and biotechnology.
Figure 2. Visible light spectrum of PS-b-P2VP stabilizing Au
NPs. The inset images show a photograph of toluene solution
of Au NPs and a TEM image of them.
The solution was stirred overnight to form block copolymer
micelles. Hydrazine (0.1 mL) was dissolved in 20 mL of toluene,
and degassed the same as the micelle solution. The micelle solu-
tion was poured into the vigorously stirred hydrazine solution.
After addition of micelle solution, the solution color suddenly
changed from yellow to deep red. This color change indicates
that nanosized Au particles having local plasmonic absorption
bands were formed. The PS-b-P2VP stabilizing Au NPs were
characterized by UV–vis spectroscopy and transmission electron
microscopy (TEM, H-7650, Hitachi).
References and Notes
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Figure 2 shows the UV–vis spectrum of Au NPs in toluene.
Absorption at 530 nm attributed to the plasmon resonance of the
Au NPs is clearly observed. The inset photograph shows the red-
colored toluene solution of Au NPs. A TEM image of Au NPs on
a Cu grid covered with a collodion membrane is shown in the in-
set of the Figure 2 (right side). The image shows that 10:1 ꢂ
2
:7 nm Au NPs have been prepared.
The toluene was evaporated from the solution of PS-b-P2VP
stabilizing Au NPs and then dissolved in THF to prepare 0.1
mg mL solution. PMMA was also dissolved in THF at the
same concentrations. Four milliliters of water was added into
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mL of THF solution of a 1:3 mixture of Au NPs and PMMA.
After evaporation of THF at room temperature, an aqueous dis-
persion of particles was obtained.
Inner structures of the particles were observed by using a
transmission electron microscope (TEM) or a scanning transmis-
sion electron microscope (STEM, S-5200, Hitachi). The average
particle size was 393 ꢂ 70 nm calculated from TEM image.
Figures 3a and 3b show a SEM (a) and a dark field STEM image
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(
b) of the composite particles. The particle has spherical shape
with densely packed Au NPs located internally. The white shell
of the particle is attributed to the PMMA moiety, which has
lower electron density than Au NPs. These images indicate that
a clear core–shell phase-separation structure has formed. The
cross-sectional TEM image (Figure 3c) shows that the core part
of the particle is filled with Au NPs. The average size of core was
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339 ꢂ 78 nm.
Published on the web (Advance View) September 5, 2009; doi:10.1246/cl.2009.964