Stoichiometric Control of Shear Alignment and Photochemical Locking for Stable Actuation in Aza-Michael Liquid Crystal Elastomers

Liquid crystal elastomers (LCEs) exhibit reversible thermomechanical deformation through changes in liquid-crystalline order. In aza-Michael LCEs, the acrylate:amine stoichiometric ratio determines residual acrylate content, oligomer molecular weight, precursor relaxation time, and UV-mediated orientation locking. Here, we investigate stoichiometric effects on shear alignment, photochemical locking, and cyclic actuation stability in aza-Michael LCEs. Precursors with different acrylate:amine ratios are prepared by oligomerization and characterized by acrylate conversion, molecular weight distribution, and thermal transitions. After selecting a common shear-alignment temperature, characteristic relaxation times are obtained from frequency sweep measurements. Constant shear-rate experiments evaluate alignment under fixed processing conditions, while constant Weissenberg number experiments account for differences in precursor relaxation time. The final order parameter after UV curing is quantified to compare the fixation efficiency of shear-induced orientation across stoichiometric compositions. UV delay experiments and photorheology relate precursor relaxation and curing behavior to the locked orientation. The locked orientation, creep-recovery response, and cyclic thermal actuation are then correlated to evaluate how residual-acrylate-mediated secondary crosslinking affects residual strain accumulation and actuation strain retention.