Antiferroelectric alignment and mechanical director rotation in a hydrogen-bonded chiral SmCA* elastomer

A new type of chiral smectic elastomer based on poly [4-(6-acryloyloxyhexyl oxy)benzoic acid] is discussed. The layer structure and the molecular tilt stabilized by hydrogen bonding between side groups are identified by X-ray measurements. Well aligned and optically clear monodomain samples with smec tic layers in the film plane are obtained by uniaxial stretching and then f rozen-in by additional gamma-radiation crosslinking. In this monodomain sta te. two opposite orientations of director tilt are distributed through the sample thickness and alternate between neighbouring layers in a zigzag fash ion. This structure of the stress-aligned chiral smectic C elastomer is sim ilar to that of antiferroelectric liquid crystals of the smectic C-A*, type . Further mechanical stretching in the layer plane induces a gradual c-dire ctor reorientation along the new stress axis, when a threshold deformation similar to 20% is exceeded. The (reversible) transition proceeds as a direc tor azimuthal rotation around the smectic C cone, with the layers essential ly undistorted and the tilt angle of the side mesogenic groups preserved.