Thermomechanical response of liquid crystal elastomers: role of crosslinker density

In this work thermomechanical properties of main-chain liquid crystal elastomers (MC-LCEs) with different degrees of crosslinking were investigated, and gradual loss of thermomechanical response was observed on repetitive measurements. Specifically, six samples of MC-LCEs were prepared, with crosslinker-to-mesogen relative concentration ranging from 5% to 10% in steps of 1%. The obtained results were then compared to thermomechanical response of side-chain liquid crystal elastomers (SC-LCEs). Additionally, thermomechanical response of polymer dispersed main-chain liquid crystal elastomers (MC-PDLCEs) was investigated. Results indicate that in MC-LCEs the concentration of crosslinker defines thermomechanical response and affects stability of the system. The loss of thermomechanical response is negligible in the case of crosslinker to mesogen ratio being the smallest, namely in 5% sample, and it is unaffected by glasslike to nematic phase transition. SC-LCEs do not show any sign of such behaviour and remain stable after several cycles of thermomechanical measurements.