Rheodielectric study on shear-induced structural change in the smectic-A phase of 4-n-octyl-4'-cyanobiphenyl (8CB).

Simultaneous measurements of rheological and dielectric properties are made to investigate shear-induced structural change in the smectic-A phase of 8CB (4-n-octyl-4'-cyanobiphenyl). With increasing the shear rate, the fluidity changes from non-Newtonian to Newtonian flow via an unstable flow region, accompanied by a characteristic change in the dielectric permittivity. In the non-Newtonian flow region, a dielectric dispersion, which can be ascribed to an undulation motion of smectic layer, is recognized. On the basis of these results, it is suggested that with increasing the shear rate the undulation changes to a chaotic structure, which is followed by a more simple structure with the layer normal along the neutral axis, and that these structural changes are responsible for the fluidity change.