Light-driven topographical morphing of azobenzene-doped liquid crystal polymer films via tunable photo-polymerization induced diffusion

Photo-polymerization is a convenient way to fabricate azobenzene-doped liquid crystal glassy polymeric networks. During the photo-polymerization process, monomer diffusion is initiated if mesogens with different reactivities are blended in the monomer mixture and the polymerization light intensity is not uniform. Upon the diffusion of liquid crystal monomers and azobenzenes, compositional inhomogeneities are introduced in the polymerized network, leading to stiffness and photo-responsivity gradients. However, the relation between this diffusion process, the resulting compositional gradients and the final light-triggered deformation is not well-understood. Here we developed a computational model to simulate the monomer diffusion and its effect on the mechanics of light-induced topographical switching. By demonstrating light-switchable folding motions and surface transformations of liquid crystal films with various molecular alignments, the photo-responsivity gradient is found to play a major role in modulating the switching performance. Furthermore, the photo-polymerization diffusion can be an effective approach to introduce spatially-varying material properties and to tailor the surface and film deformations by varying the wavelength, illumination area and polarization of the incoming light. The proposed framework can be used to evaluate and control photo-polymerization-induced monomer diffusion to tune light-triggered topographical morphing.