Induction of liquid crystal orientation through azobenzene-containing polymer networks

A diacrylate monomer containing a core of azobenzene groups was synthesized. Thermal polymerizations of mixtures of the monomer dissolved in a nematic liquid crystal, E7, resulted in liquid crystals stabilized by an azobenzene-containing polymer network. When their thin films were irradiated by linearly polarized UV light at room temperature, as a result of the alignment of azobenzene groups on the network, a macroscopic orientation of E7 molecules was induced perpendicular to the UV polarization direction. Infrared dichroism was used to measure the liquid crystal orientation in irradiated films. It was found that the achievable orientation, observed after minutes of irradiation, increases with increasing polymer network density and that a significant degree of the induced orientation remains stable after turning off the irradiation. This approach represents a new means to control the average liquid crystal orientation in materials such as polymer-stabilized liquid crystals.