Solid-like Properties of Liquid Crystal in Smectic Phase Controlled with Electric Field Applied

Electro-rheological characteristics of a liquid crystal (8CB) in smectic-A phase were investigated utilizing a parallel-plate type rheometer under the stress control mode. Solid like behavior of the liquid crystal under DC or AC electric fields were mainly examined. Bingham-like properties were observed and yield stress measured was affected with the electric field conditions. When the electric field strength was low, the yield stress was almost the same as that obtained under no electric field. Above a threshold of DC electric field, the yield stress increased and then became constant. An opposite tendency was observed under AC electric fields. In order to clarify the yield process in detail, the structure of the liquid crystal between two parallel plates was directly observed with a polarizing optical system. Under the DC electric fields, we found there were partially collapsed structures at the first stage of yield process and then largscale deformation was generated. We had also conducted a strain recovery test under small strain conditions where the partially collapsed structures were observed. It was found that the structure in this region had partially elastic recoverable strain.