Influence of Orientational Genesis on the Actuation of Monodomain Liquid Crystalline Elastomers
Tayler S. Hebner, Christopher N. Bowman, Timothy J. White
Abstract
The macroscopic alignment of the nematic director within liquid crystalline elastomers (LCEs) amplifies the magnitude of the directional strain response. Theory predicts that the stimuli response of LCEs will be affected by the orientational genesis of cross-linking. We examine compositionally identical LCEs aligned by either mechanical or surface techniques. The two-step procedure to prepare LCEs by mechanical alignment first forms cross-links in a disordered state (e.g., isotropic orientational genesis), which thereafter are aligned by deformation during which polymerization (e.g., cross-linking) is completed. Comparatively, cross-linking within surface-aligned LCEs exclusively occurs within the ordered state (e.g., nematic orientational genesis). The orientational genesis of cross-linking in aligned LCEs, in compositionally identical samples, significantly affects the thermotropic and phototropic deformation of these materials. LCEs prepared by mechanical alignment (e.g., isotropic orientational genesis) have actuation temperatures that are as much as 75 °C lower than the analogous LCEs prepared by surface alignment (e.g., nematic orientational genesis). Likewise, the magnitude and rate of photoinduced strain generation in azobenzene-functionalized LCEs prepared by mechanical and surface alignment differ by a factor of 2 or greater.