Enhanced surface topographies in liquid crystal polymer networks

Liquid crystals can easily be aligned in the desired direction and their molecular orders can be changed by an external stimulus such as light. This movement in a molecular level provides detectable changes in surface topography. In this study, light-responsive azobenzene doped liquid crystal polymer networks supported by soft polymeric substrates were designed as smart layered systems. Since most studies conducted related to smart coatings have focused on the use of glass plates as a bottom layer, the first aim of the study was providing suitable combination of the layers. The second aim was enhancing polarized light-triggered oscillating surface topographies. In the case of enhancing such systems, it would be interesting to design haptic screens giving responses to users, or solar panels having self-cleaning surfaces. Both mechanically rubbed layers and photoalignment layers were used to align liquid crystals. Implemented substrates were oxygen plasma treated polydimethylsiloxane (PDMS), acrylate-based tetra(ethylene glycol) diacrylate (TTEGDA) having different pre-curing times and TTEGDA including different volume concentrations of monomer 2-ethylhexyl acrylate (2-EHA). Acrylate-based systems showed better optical anisotropy than PDMS supported substrates. Moreover, it was observed that increasing the amount of 2-EHA decreased the storage modulus of the acrylate-based substrates, and thus increased the softness of the materials. For each type of alignment layer, the best oscillation results were achieved using a mixture of 95% 2-EHA and 5% TTEGDA. For mechanically aligned uniaxial azo-LCPN, the highest surface deformation and amplitude of the oscillation were measured as 102.8 and 18.8 nm, respectively. For photo-aligned azo-LCPN which has perpendicularly oriented liquid crystal molecules to each other (500 µm periodic domains), the stable surface deformation and amplitude of the oscillation were measured as 360 and 86 nm, respectively. Keywords: Azobenzene, liquid crystals, light-responsive liquid crystal polymer networks, surface topography, smart coatings.