Effective Reflective Indices of Polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) Lamellar Films

Abstract

Block copolymers have drawn increasing attention for fabricating functional nanomaterials due to their properties of self-assembly. Especially, photonic crystals hold promise for multiple optical applications. We prepared 1D photonic crystals with polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) lamellar films which is hydrophobic block-hydrophilic polyelectrolyte block polymer of 57 kg/mol-b-57 kg/mol. The lamellar stacks, which are alternating layers of hydrophilic and hydrophobic moiety of PS-b-P2VP, are obtained by exposing the spin coated film under chloroform vapor. The band gaps of the lamellar films interestingly varied after immersion into the quaternizing solvents containing 5 wt% of iodomethane solubilized in n-hexane. To study of spectral characteristics, UV-visible absorption spectra were measured as a function of the incidence angle (in 10 degrees steps) at swollen films with distilled water and ethanol. The UV-visible maximum absorption spectra shifted by Bragg's law. From transmission spectra, effective refractive index of the photonic crystal was calculated based on the modified Bragg-Snell law.