Mechanism of strain retention and shape memory in main chain liquid crystalline networks

Abstract

Abstract Liquid crystalline networks (LCNs) are described in which there is anelasticity in strain recovery response (under zero load) after uniaxial tensile loading. This strain retention is shown as a function of time after release of load and is further characterized by thermal, X‐ray, and stress/strain experiments. It was found that, at temperatures in the smectic phase far below the isotropization temperature, this LCN film retains significant levels of strain when in the monodomain state. On free recovery (zero load) of the LCN film there is a rapid elastic response followed by a slow anelastic response for those films that had undergone a polydomain‐to‐monodomain transition during the initial imposed strain regimen. It is postulated that the mechanism leading to the strain retention involves nanosegregation‐driven pinning of unfolded hairpins in shallow energy wells and that this effect is responsible for the thermally activated recovery of strain (shape memory) at elevated temperatures. magnified image Stress–strain curves of pre‐strained C11(MeHQ)Si8XL10 LC networks having various initial strains: (a) 350%, (b) 300%, (c) 250%, (d) 200%, (e) 150%, (f) 100%, and (g) 50%.