Curvature in nematic elastica responding to light and heat

Abstract

Nematic elastic bodies can develop a gradient of response to heat, light and other stimuli. They then bend and develop curvature in a complex manner depending on director field distributions, on whether they are monodomain or polydomain structures and on linear or nonlinear light absorptive processes. In each case, we derive the general weak response where bend in each direction is treated independently of that in others. In a subsequent paper, we address the reverse phenomenon, that is of strong spontaneous distortion leading to curvature suppression.

Programmed morphing of liquid crystal networks

“…For twisted films, at z ¼ 0 contraction along the x-axis and expansion along the y-axis takes place, while the opposite happens at z ¼ h. This leads to an anticlastic deformation with negative Gaussian curvature (Fig. 2a) [19]. However, such curvature leads to stretches due to the curvature in the x direction working against the curvature in the y direction and vice versa.…”

Gaussian curvature from flat elastica sheets

“…Of course, simple bend can occur if deformation is non-uniform through the sheet's thickness. Typically, though the bend is in one direction only, with limited saddle or spherical response, a wide range of new possibilities are reviewed and modelled (Warner et al 2010a). However, Gaussian curvature is soon suppressed (Warner et al 2010b) by the stretches mentioned above.…”

Suppression of curvature in nematic elastica

“…Bend results from a spatial variation of mechanical response through the thickness of a sheet or cantilever of the active material. In an accompanying paper (Warner et al 2010) (WMCI), we have catalogued the ways in which non-uniform strains can arise, and have calculated what weak bending results.…”