Mechanically induced tilt in smectic-A elastomers

Abstract

Recently it has been predicted that shear forces can unlock the director and the layer normal in smectic-A elastomers, leading to a smectic-C like tilt analogous to the electroclinic effect of chiral S_A* phases. In order to investigate this phenomenon, we present detailed X-ray investigations of S_A elastomers under shear, comparing networks of different chemical constitution. Upon shear imposed in the layer planes, an induced S_C like tilt is observed, which develops linearly with the applied shear angle. With decreasing layer compression modulus B of the smectic network, the effect becomes smaller, and additional layer rotations are found. For elastomers containing fluorinated mesogens, layer normal and director are rigidly locked, despite their large B modulus, and the phase structure remains unchanged under shear strain. The experimental results provide clear evidence for recent theoretical predictions.