Photocrosslinkable Nanocomposite Multilayers for Responsive 1D Photonic Crystals

A straightforward method to increase the refractive index of photocrosslinkable polymers by incorporation of high index inorganic nanoparticles is demonstrated and shown to enhance the reflection efficiency of thermochromic 1D photonic multilayers. The refractive index of spin-coated and UV-crosslinked films based on poly(para-methyl styrene) (PpMS) copolymers is increased from 1.57 for the copolymer alone to as high as 1.67 for nanocomposite samples with a volume fraction of 0.38 of ZrO2 nanoparticles. Thermochromic photonic multilayers consisting of alternating films of PpMS-ZrO2 with poly(N-isopropylacrylamide) (PNIPAM) copolymers shows the increases in reflectance as large as 2.5-fold compared to PpMS/PNIPAM multilayers lacking particles. In addition, ZrO2 nanoparticles are used to increase the refractive index of PNIPAM-based films up to 1.68 with a volume fraction of 0.49 of nanoparticles, enabling the fabrication of alternating PNIPAM-ZrO2/PNIPAM multilayers with a well-defined Bragg peak that shifts from 635 nm at 6 degrees C to 410 nm at 48 degrees C, and reflectance intensities as high as approximate to 0.30.