Mesogen alignment in liquid crystal elastomer (LCE) microparticles under mechanical stress: experiments and simulations

When subjected to mechanical stress, liquid crystal elastomers (LCEs) undergo semi-soft deformations and the director field aligns in the direction of strain. The optical morphology gives distinct patterns corresponding to the stress field, thereby offering potential applications as stress-sensing devices. While the strategy can be employed at the microscopic scale, investigations to date have almost exclusively focused on LCEs in bulk, and the effect of geometric confinement has received little attention.

In this work, we study micron-sized LCE particles that were synthesized via dispersion polymerization. The particles display unique polarized optical textures under compression, shear and uniaxial extension. The particles' aspect ratio can be programmed by stress and controlling the crosslinking density. Finally, in order to model the stress-induced alignment and the defect formation process, we adopt a tensorial representation of the local order parameter and finite element discretization to describe the evolving geometries. The director field relaxation is obtained through a Ginzburg-Landau relaxation, where the free energy functional includes contributions from nematic elasticity, strain, memory effects, and coupling between the strain and the local ordering. By combining experiments and simulations, we build a detailed understanding on how the mesogen alignment evolve under external stress thereby facilliating LCE applications at microscopic scales.