Uniaxial and shear deformations in smectic-C main-chain liquid-crystalline elastomers

A novel cross-linked smectic-C main-chain liquid-crystalline elastomer has been synthesized by polycondensation of vinyloxy-terminated mesogens, tetramethyldisiloxane and pentamethylpentaoxapentasilecane. The introduction of the functional vinyloxy group allows the synthesis of well-defined networks having low soluble content and good mechanical properties due to elimination of side reactions as in the case of vinyl groups. Networks having a macroscopic uniformly ordered director and a conical distribution of the smectic layer normal with respect to the director are mechanically deformed by uniaxial and shear deformations. Under uniaxial deformations two processes were observed: parallel to the director the mechanical field directly couples to the smectic tilt angle while perpendicular to the director a reorientation process takes place. A shear deformation parallel and perpendicular to the director causes a uniform layer orientation and the network exhibits a smectic-C monodomain phase having a macroscopic uniform director and layer orientation. This process is reversible for shear deformation perpendicular and irreversible, by applying the shear force parallel to the director.