Liquid crystal elastomer balloons

We describe a setup for mechanical measurements of smectic liquid crystal elastomers and study two materials with different network topologies. The elastic response of macroscopically oriented smectic elastomers to a two-dimensionally isotropic stress in the film plane is measured. The experimental method is based upon the measurement of the inner excess pressure of elastomer balloons, produced by inflation of thin freely suspended films of the smectic material to spherical shape and subsequent photo-cross-linking. We discuss the effects of entropic rubber elasticity and smectic layer compression in the experiment and analyze influences of the network topology (2D or 3D) on the elastic behavior.