Formation of lamellar domains in liquid crystal elastomers under compression

Abstract

Liquid crystal elastomers (LCEs) are lightly cross-linked polymer materials containing liquid crystal (LC) molecules with unique strain-induced director reorientation properties. Compressive studies on LCEs have been very little given the difficulty synthesizing sufficiently large monodomain block samples. Based on the continuum mechanics model of LCEs, the compressive behaviors of monodomain LCE blocks in plane stain with different initial directors between two rigid plates are systematically studied in this paper. The rotation of the director, especially the formation of lamellar domains, significantly changes the characteristics of the compressive stress-strain curves. Compression along the initial director will induce the formation of lamellar domains orthogonal to the loading axis due to the alternating rotation of the director after loading to a critical strain. The rotation of the director also leads to the stress plateau on the stress-strain curves. When the initial director is nearly parallel to the compression axis, the lamellar domains can still be observed in the central region of the sample bonded to the rigid plates, which is also related to the deformed morphology of the stress-free boundaries. If the initial director is slightly deviated from the loading axis, almost uniform rotation occurs in the central region of the sample, while the stress increases monotonically with strain hardening. The formation of lamellar domains is not only related to the angles between the initial director and the compressive loading axis, but also strongly depends on the geometrical and material parameters of the samples. For large aspect ratios or small anisotropy constants, the formation of lamellar domains may require compression sufficiently parallel to the initial director. Our work provides a deeper understanding of the behavior of LCEs under compression.