Investigation of Liquid Crystal Alignment on Polybutylmethacrylate Surfaces using FTIR-ATR and XPS

Conoscopy studies have shown that poly(n-butylmethacrylate) (PNBMA) causes LC molecules to align homogeneously (parallel alignment) to the surface while poly(iso-butylmethacrylate) (PIBMA) causes LC molecules to align homeotropically (perpendicular alignment) to the surface. This alignment switch occurs when the polymer composition is greater than 40% PIBMA. Fourier transform infrared-attenuated total reflectance (FTIR-ATR) analyses have been done to examine the chemical interactions occurring at the polymer/LC interface as a function of substrate composition. No unique peaks are present in the FTIR spectra for the LC/polymer interface, yet there are subtle differences in peak shape, position, or intensity. These polymer substrates have also been examined by X-ray photoelectron spectroscopy (XPS), using valence band spectra to determine the surface composition. The XPS studies indicate that mixtures of PIBMA and PNBMA are enriched in PIBMA at the surface.