Photoinduced Alignment Behaviors of a Nematic Liquid Crystal on Azobenzene Langmuir-Blodgett Monolayers

Trans/cis photoisomerization of azobenzene (Az) molecular films on the substrate is capable of inducing homeotropic/planar alignment changes of nematic liquid crystals (LCs). These photofunctional surfaces are called "command surfaces." (Fig.1)1 The Langmuir-Blodgett (LB) technique provides importance information on the design of the surface layer. The LB film preparation condition should influence, to a large extent, the aligning behavior of the nematic LC as formerly proposed by Hiltrop and Stegemeyer.2 The present work is undertaken to elucidate the relationship between the conditions of the LB film conditions and the LC aligning behaviors. For Az LB film preparation, two sets of amphiphilic Az side chain polymers are employed, the backbone being (i) poly(vinyl alcohol) and (ii) poly(ethyleneimine). Polymeric materials are required to obtain highly photoreactive Az LB films. Single monolayers are prepared as the Az LB films throughout the investigation to avoid complexity of the film structure.