固体的特性を有するスメクティック液晶のエレクトロレオロジー(<小特集>非ニュートン性,機能性を示す複雑流体の流動と応用)

Abstract

The ER characteristics of a liquid crystal (8 CB) in smectic-A phase were investigated utilizing a parallel-plate rheometer under a stress control mode. The steady flow properties and solid like behavior of the liquid crystal under DC or AC electric fields were examined. Although the liquid crystal in nematic phase under steady shear flow showed the normal ER effect, i.e. increase in apparent viscosity under electric field, the viscosity in smectic phase exhibited an opposite effect in low shear rate region. Moreover, Bingham-like properties were observed in smectic phase and the yield stress obtained was affected by the electric field. 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. It appears that the smectic poly-domain structure is maintained under lower electric field conditions and has become more orderly and stronger under higher DC electric fields. By contrast, the AC electric field would generate more slippery layered structure because of the alternating electrical current on the molecules.