Photo-responsive azo-functionalised flexible polymer substrate for liquid crystal alignment

An azobenzene derivative containing a dimethylchlorosilane end group was chemically attached to a flexible polymer substrate to create permanent photo alignment layer. The commercially obtained polymer substrate (overhead projector film) was characterised and found to contain cellulose acetate as the main component. Surface functionalization of the substrate was confirmed through X-ray photoelectron spectroscopy (XPS), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (CA) and atomic force microscopy (AFM) techniques. Photo-isomerisation behaviour of the azo-layer on the polymer substrate was additionally confirmed by UV-diffuse reflection spectroscopy (UV-DRS). Further, the azo-modified flexible substrate was analysed for the orientation of the bulk liquid crystal (LC) sample and tuning the LC orientation by utilising photo-switching behaviour of the azo-layer on the substrate.