Light-Induced Formation of Dynamic and Permanent Surface Topologies in Chiral-Nematic Polymer Networks

We report a procedure and a material to make patterned surface topologies by light, both in a dynamic way where the structures disappear after exposure or such that the deformations remain permanently. The method is based on a photosensitized cross-linked liquid crystal network with chiral-nematic molecular order. The polymer network is made photoresponsive by a small concentration of copolymerized azobenzene monomers. Upon exposure with patterned UV light, the molecular order parameter in the network is decreased by the trans-to-cis isomerization of the azobenzene, resulting in a density decrease and corresponding local volume increase. Under normal conditions, the polymer network behaves fully elastic and the surface deformation is fast and reversible. To induce permanent deformation, the polymer network needs to be adjusted by chain transfer agents to control the kinetic chain length of the network main chains and allow out of the plane reorientation of the azobenzene moieties and a corresponding loss of molecular order.