Polymeric nanocomposites as photonic sensors

Abstract

Hydrogel-coated refractive nanoparticles can self-assemble to form perfect colloidal crystalline array (CCA), which can act as a photonic sensor in visible and near-infrared region triggered by temperature. The aim of this study was to tune the lattice parameters of these CCAs made of poly-(N-isopropylacrylamide) coated silica nanoparticles and hence their sensor properties by varying various factors. The synthetic scheme of this work involves surface modification of silica nanoparticles followed by radical polymerization to obtain polymeric nanocomposites. Photon correlation spectroscopy (PCS) was used to measure the particle size of these nanocomposites with temperature variation and a sharp decrease from 1094.8 nm to 506.8 nm at the LCST (lower critical solution temperature) region was observed, which can be attributed to volume-phase transition. Atomic Force Microscopy (AFM) images complemented these results. Reflectance measurements were performed to obtain the position of photonic stop-bands as a function of temperature as well as core particle size, which can be explained with the help of Bragg's diffraction equation. With temperature increase the stop band shifted towards lower wavelength due to hydrogel collapse at elevated temperature, whereas the core particle size was directly proportional to the position of the stop band. In conclusion, self-assembly was proven to be a very simple and cost-effective approach for making photonic sensors made of polymeric nanocomposites and their sensor properties can be effectively tuned by varying certain factors.