NEMD Simulations of Shear-Induced Orientation Switching in Smectic Liquid Crystal Elastomers

We investigated shear-induced orientation switching in smectic liquid crystal elastomers (LCEs) using non-equilibrium molecular dynamics (NEMD) simulations to complement recent direct ink writing (DIW) experiments. Experimentally, smectic inks show a transition from perpendicular to parallel director alignment with increasing print speed, governed by the interplay of smectic layering and flow. To elucidate this mechanism, we simulated rod-like mesogens under shear using a dissipative particle dynamics thermostat in a triclinic cell. The simulations reproduce the experimentally observed orientation inversion and identify a critical shear rate where smectic layers distort and collapse, triggering reorientation of the director along the flow direction. Below this threshold, intact layers slide past each other while maintaining strong orientational and translational order. Analysis of the translational and orientational order parameters and layer tilt angle reveals a gradual shear-driven smectic–nematic transition consistent with an entropy-dominated mechanism. These findings link print parameters, local shear rate, and molecular orientation, providing microscopic insight for controlling alignment in 3D-printed smectic LCEs.