Fabrication of Colloidal Crystal Gel Film Using Poly(N-vinylcaprolactam)

In this report, we successfully fabricated the colloidal crystal (CC) gel films of silica microparticles combined with a temperature-responsive biocompatible hydrogel of poly(Nvinylcaprolactam) (VCL). When the CC VCL film was prepared by filling VCL precursor into the void space between silica particles of CC film, followed by the thermal polymerization, the Bragg reflection peak was red-shifted from 475 nm to 535 nm due to the change of refractive index contrast. Subsequently, immersion of the CC VCL film into an excess of water led to the formation of CC VCL gel film, wherein the VCL matrix swelled in water to form the hydrogel state. As elevating the temperature from 25 °C, this CC VCL gel film showed the reflection color changes from red to green, arising from the decrease of lattice constant induced by the shrinkage of VCL hydrogel. Moreover, the reflection color changes of CC VCL gel film were found to be fully reversible. In this way, we believe that such CC VCL gel films can be potentially applied to novel temperature sensors with biocompatibility.