Near-Zero Azimuthal Anchoring of Liquid Crystals Assisted by Viscoelastic Bottlebrush Polymers

In this article, we revealed the mechanism of weak anchoring properties of liquid crystals (LCs) on cross-linked films of bottlebrushes consisting of poly(hexyl methacrylate) (PHMA) and poly(ethyl methacrylate) (PEMA). First, azimuthal anchoring coefficients, A2, of a LC were estimated using these two systems from the voltage-transmittance curves at different temperatures. The PHMA and PEMA systems showcased a temperature-dependent weak anchoring property, with A2 decreasing as the temperature was increased. Second, the degree of swelling of these two systems (with cross-linked films) by the LCs was determined and compared with the phase diagrams of the corresponding mixtures without cross-linking, suggesting that the relaxation dynamics of side chains of bottlebrushes was retained even after the cross-linking. Finally, rheological measurements were conducted for the LC/bottlebrush mixtures to discuss the dynamics of the LC-swollen cross-linked bottlebrush films, which clearly demonstrated the relaxation behavior of the side chains. Assuming the time scale for the determination of A2, the characteristic temperature corresponding to the side-chain motion was reasonably correlated with the decreasing temperature behavior of A2. As a consequence, weak anchoring could be explained by the polymer chain dynamics, which was revealed to be accelerated by the bottlebrush architecture as well as the swelling with LCs, depending on the affinity of the bottlebrush component with the target LC.