Stress‐optical and thermomechanical measurements on liquid crystalline elastomers

For liquid crystalline polysiloxane‐elastomers, the orientation of the mesogenic side groups is determined under uniaxial compression and without load in the isotropic state in the vicinity of the isotropic to nematic phase transformation. The experimental results clearly indicate the following fundamental properties of liquid crystalline elastomers: Depending on the chemical constitution of the flexible spacer a mechanical force causes a macroscopic orientation of the mesogenic side groups parallel or perpendicular to the direction of the force. Strain causes a parallel (perpendicular), while compression causes a perpendicular (parallel) orientation of the side groups with respect to the direction of the mechanical force. Due to a macroscopic orientation of the mesogenic side groups in the liquid crystalline state, the physical properties of the elastomers become anisotropic, which is directly reflected in the thermomechanical properties.