Spontaneous shear flow induced by electrohydrodynamic convection of NLC and hysteresis loop

Abstract

Recently, we have found that the upper plate of a rheometer spontaneously rotates when a nematic liquid crystal MBBA is sandwiched between the two parallel plates and an ac electric field is applied to the sample to generate electroconvection. The spontaneous rotation indicates the existence of negative shear stress and furthermore hysteresis loop of the shear stress vs. the shear rate. We have successfully observed hysteresis loops similar to those observed in ferroelectric and ferromagnetic materials. We also found that all the hysteresis loops with different electric fields fall on a universal loop when both the shear stress and the shear rate are scaled by squared electric field.