Atomic force microscopic studies of the influence of stretching on thin oriented films of ferroelectric liquid crystalline elastomers

To analyze the impact of the molecular structure on the network formation in ferroelectric liquid crystalline polymers, two copolymers are studied, which are identical except for the molecular position of the cross-linkable group: (i) Polymer P1 with cross-linkable groups attached to the backbone via a short spacer and (ii) Polymer P2 with the cross-linkable group in terminal position of a mesogenic side group. When mechanical stress is imposed on thin films in homeotropic orientation through stretching, the two elastomers react differently to the deformation, as seen by AFM imaging of the surface topology: For Polymer P1, “intra-layer” cross-linking results in two dimensional networks in each backbone layer, separated by liquid-like FLC sidegroup layers. As there are practically no vertical connections in this intralayer network, no vertical distortions occur. In Polymer P2 a three dimensional, “inter-layer” network is formed; the system reacts with a distortion of the smectic layering.