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 SA* phases. In order to investigate this phenomenon, we present detailed X-ray investigations of SA elastomers under shear, comparing networks of different chemical constitution. Upon shear imposed in the layer planes, an induced SC 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.