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. 2009 Oct 13;21(19):4608-4613.
doi: 10.1021/cm901666b.

Fabrication of Silica Shell Photonic Crystals Through Flexible Core Templates

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Free PMC article

Fabrication of Silica Shell Photonic Crystals Through Flexible Core Templates

Luling Wang et al. Chem Mater. .
Free PMC article

Abstract

We attached very small silica particles onto flexible monodisperse poly (N-isopropylacrylamide, PNIPAm) core particles synthesized by dispersion polymerization. These silica particles were attached to the partially swollen PNIPAm particles by the hydrolysis and condensation of tetraethoxysilane at 24 °C. The resulting silica particle-functionalized PNIPAm core particles show reversible swelling and shrinking as the temperature is cycled. These particles form close-packed-array photonic crystals as the solvent evaporates; the cores shrink to form a silica shell around the pure PNIPAm dry core particles as they close pack. The PNIPAm cores were removed by calcination, leaving a PC composed of essentially pure continuous silica shells. These silica shell photonic crystals Bragg diffract UV light at ~310 nm. The close packed particle interstices are continuous and are easily filled by water. In contrast, the silica shells are impervious to water because the process of making them results in a continuous shell of silica without holes.

Figures

Scheme 1
Scheme 1
Preparation of silica shell photonic crystals
Figure 1
Figure 1
a) TEM image of PNIPAm core particles; b) Photograph of Bragg diffraction from PNIPAm core particles
Figure 2
Figure 2
Temperature dependence of diameter and turbidity of PNIPAm particles
Figure 3
Figure 3
TEM of PNIPAm core particles after silica coating at a), pH 11.0 and b), pH 8.0 (the insert shows a core-shell particle at higher magnification, the scale bar is 500 nm)
Figure 4
Figure 4
Temperature dependence of the DLS measured apparent particle diameter of the PNIPAm-silica core-shell particles (solid line drawn to help the eye)
Figure 5
Figure 5
SEM of (a) unordered and (b) ordered close-packed silica-shell/PNIPAm-core particles
Figure 6
Figure 6
(a) SEM image of the cross section of silica shell photonic crystals, (b) TEM image of the silica shell photonic crystals
Figure 7
Figure 7
Reflectance spectrum of silica shell photonic crystals in air (solid line) and water (dash line)

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