Mechanical deformation behavior in highly anisotropic elastomers made fromferroelectric liquid crystalline polymers

Cross-linked ferroelectric liquid crystalline polymers are studied by atomi c force microscopy. Polysiloxane copolymers have been synthesized with meso genic and photo-cross-linkable side groups, the latter connected either dir ectly to the backbone via a short spacer or as terminal groups on a part of the mesogens. Although the polymers are otherwise identical, the restricti ons imposed on the network formation process by the anisotropy of the smect ic mesophase are different for the two positions of the cross-linkable grou p: In the first case ("intralayer cross-linking"), a predominantly two-dime nsional network is formed in the backbone layers separating the smectic lay ers; in the second case ("interlayer cross-linking"), a primarily three-dim ensional network is established which is dependent on the mesophase of cros s-linking. These elastomers are prepared as thin freely suspended films in homeotropic orientation. The topography consists of plateaus separated by s teps of characteristic height, corresponding to the surfaces and edges of s mectic layers. If a film of "intralayer cross-linked" elastomer (network fo rmation in the microphase-separated backbone layers) is elongated, the laye rs can slide on one another, showing occasional tears but no surface roughe ning (roughness 0.5 nm at 30% elongation). In an "interlayer cross-linked" film (network formation via the mesogens), the three-dimensional network in troduces forces perpendicular to the direction of the mechanical deformatio n, leading to a characteristic depression pattern on the surface which indi cates a distortion of the smectic order.