Unlocking entropic elasticity of nematic elastomers through light

Abstract

Here, we show that entropic elasticity fully recovers after photo-isomerization of azobenzene units incorporated in a nematic LCE. With the light-induced bent cis-isomers at room temperature, the degree of soft elasticity, viscosity, and adhesion are tangibly lowered. Mechanical responses rationalize that cis isomers unlock the frozen configurational degree of freedom by reducing nematic order in the same manner observed upon temperature increase. The present results not only unveil how the nematic interaction suppresses entropic elasticity leading to the soft state, but also offer a guide to tuning viscoelasticity toward dynamic mechanical applications.