Optimizing the photomechanical performance of glassy azobenzene liquid crystal polymer networks

Glassy, polydomain azobenzene liquid crystal polymer networks (azo-LCN) have been synthesized, characterized, and modeled to understand composition dependence on large amplitude, bidirectional bending and twisting deformation upon irradiation with linearly polarized blue-green (440-514 nm) light. These materials exhibit interesting properties for adaptive structure applications in which the shape of the photoresponsive solid state structure can be rapidly reconfigured with light. The basis for the photomechanical output observed in these materials is absorption of actinic light by azobenzene, which upon photoisomerization dictates an internal stress within the local polymer network. The photoinduced disruption of the order/orientation of the local polymer network accompanying photoisomerization is manifested in a macroscopic deformation. Accordingly, this work examines the polarization-controlled bidirectional bending of highly concentrated azo-LCN materials and compares the macroscopic bending to a nonlinear photoshell model. The resulting photomechanical output is highly dependent on the concentration of crosslinked azobenzene mesogens employed in the formulation. The model comparisons illustrate differences in internal photostrain and deformation rates as a function of composition.