Manivannan Karthikeyan, Huang Yi-Shen, Huang Bohr-Ran, Huang Chih-Feng, Chen Jem-Kun
Department of Materials Science and Engineering, National Taiwan University of Science and Technology, 43, Sec 4, Keelung Road, Taipei 106, Taiwan.
Department of Chemical Engineering, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan.
Polymers (Basel). 2016 Dec 10;8(12):428. doi: 10.3390/polym8120428.
We grafted thermo-responsive poly(-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.
我们通过表面引发原子转移自由基聚合（SI ATRP）从单分散的SiO₂微球上接枝了热响应性聚（N-异丙基丙烯酰胺）（PNIPAM）刷，以生成核壳结构的SiO₂@PNIPAM微球（SPMs）。尺寸规则的SPMs分散在水溶液中，并在干燥状态下堆积成光子晶体（PCs）。由于SPMs的微观尺度，可以通过光学显微镜观察PCs在水中的堆积行为。通过将温度升高到PNIPAM的低临界溶液温度（LCST）以上，PNIPAM壳层的可逆溶胀和收缩导致SPMs在水溶液中分散和沉淀（三维聚集）。SPMs在水层中微分散，以适应二维方向上的聚集。在微分散状态下，低于LCST时，SPMs以PCs形式堆积，SPMs之间具有微观尺度的间距。当温度升高到LCST以上时，微分散的PCs在二维方向上呈现紧密堆积排列，SPMs之间的间距减小。随着温度升高到LCST以上，间距的变化导致颜色从红色变为蓝色，在一定入射角下肉眼即可观察到。因此，SPM阵列可作为视觉温度传感器应用。
