Control in Coloration and Estimation of the Refractive Index by Porous Polymeric Membranes Prepared by the "Miniemulsion" Templating Method

We fabricated porous polymeric membranes using the miniemulsion templating method to investigate the transmitted and scattered lights in terms of the Christiansen filter effect. This method made it possible to produce porous polymeric membranes with different refractive indices by polymerization of different monomers and copolymerization of monomers. When a membrane with an open-cellular structure was immersed in a liquid, the transmitted light was observed at a wavelength where the refractive indices of the polymeric phase and the liquid matched. Angle-independent color derived from the scattered light could also be observed. When the porous membrane of poly(2-ethylhexyl methacrylate) (EHMA) was immersed in a mixture of different kinds of liquids, the maximum wavelength of the transmission (λmax) changed according to the refractive index matching of the polymeric phase and the liquid, resulting in the change in coloration. Next, when the P(EHMA-co-EGDMA) membrane was immersed in a mixture of toluene and d-limonene, λmax and color varied depending on their mixing ratios. This coloration was controlled by temperature and the refractive indices of the polymeric phase and the liquid. Furthermore, we could estimate the refractive index of PEGDMA using λmax values obtained by immersing it into liquids with different refractive indices.