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Polymers 2016, 8(12), 428; doi:10.3390/polym8120428

Real-Time Packing Behavior of Core-Shell Silica@Poly(N-isopropylacrylamide) Microspheres as Photonic Crystals for Visualizing in Thermal Sensing

1
Department of Materials Science and Engineering, National Taiwan University of Science and Technology, 43, Sec 4, Keelung Road, Taipei 106, Taiwan
2
Department of Chemical Engineering, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan
3
Graduate Institute of Electro-Optical Engineering and Department of Electronic Engineering, National Taiwan University of Science and Technology, 43, Sec 4, Keelung Road, Taipei 106, Taiwan
*
Authors to whom correspondence should be addressed.
Academic Editor: Po-Chih Yang
Received: 5 November 2016 / Revised: 29 November 2016 / Accepted: 6 December 2016 / Published: 10 December 2016
(This article belongs to the Special Issue Polymers for Chemosensing)
View Full-Text   |   Download PDF [5308 KB, uploaded 10 December 2016]   |  

Abstract

We grafted thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) brushes from monodisperse SiO2 microspheres through surface-initiated atom transfer radical polymerization (SI ATRP) to generate core-shell structured SiO2@PNIPAM microspheres (SPMs). Regular-sized SPMs dispersed in aqueous solution and packed as photonic crystals (PCs) in dry state. Because of the microscale of the SPMs, the packing behavior of the PCs in water can be observed by optical microscopy. By increasing the temperature above the lower critical solution temperature (LCST) of PNIPAM, the reversible swelling and shrinking of the PNIPAM shell resulted in dispersion and precipitation (three-dimensional aggregation) of the SPM in aqueous solution. The SPMs were microdispersed in a water layer to accommodate the aggregation along two dimensions. In the microdispersion, the SPMs are packed as PCs with microscale spacing between SPMs below the LCST. When the temperature is increased above the LCST, the microdispersed PCs exhibited a close-packed arrangement along two dimensions with decreased spacing between SPMs. The change in spacing with increasing temperature above the LCST resulted in a color change from red to blue, which could be observed by the naked eye at an incident angle. Thus, the SPM array could be applied as a visual temperature sensor. View Full-Text
Keywords: core-shell; SiO2 microsphere; structural color; photonic crystals; polymerization core-shell; SiO2 microsphere; structural color; photonic crystals; polymerization
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Manivannan, K.; Huang, Y.-S.; Huang, B.-R.; Huang, C.-F.; Chen, J.-K. Real-Time Packing Behavior of Core-Shell Silica@Poly(N-isopropylacrylamide) Microspheres as Photonic Crystals for Visualizing in Thermal Sensing. Polymers 2016, 8, 428.

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