Rheological properties of a chiral liquid crystal exhibiting type-II character

Abstract

We measured rheological properties of cholesteryl nonanoate and its mixture with 40-octyloxy-4-cyanobiphenyl. In both systems, wider temperature range of blue phase under shear with anomalous increase in viscosity associated with non- Newtonian flow behavior has been observed. Shear thinning followed by Newtonian flow is found in cholesteric phase and non-Newtonian flow behavior at high shear rates is seen in smectic-A phase. In cholesteryl nonanoate a small peak in the viscosity at cholesteric to smectic-A transition along with a shear rate dependent viscosity at higher shear rate is attributed to the type-II character of the compound. We find that the type-II character of the compound is further enhanced by mixing a small amount (20 wt%) of 40-octyloxy-4-cyanobiphenyl in cholesteryl nonanoate. No significant change in the temperature dependent rheological behavior is observed at the twistgrain- boundary-A to smectic-A transition. It is suggested that the small anomalous peak in the viscosity just above the twist-grain-boundary-A phase is due the existence of chiral line liquid phase.