Rheo-optical experiments have been carried out to study the relationship between rheological properties and structures of concentrated solutions of PBLG (Poly-γ-Benzyl-L-glutamate) in m-cresol. The flow properties of the solutions at concentrations above B-point have been observed with a rheometer equipped with quartz cone-plate, and simultaneously the transmitted light intensities (
Ix,
In and
IE) of polarized light have been measured on the sample under shear as functions of shear rate (3×10
-2-4×10
0s
-1). It has been found that the transmitted light intensity
IE (measured under extinction position of crossed polarizers system) is the most meaningful measure to know the orientation behavior and the mesophase transition of polymer liquid crystal systems.
IE is very high in the undisturbed state for all the solutions tested.
In the case of a 10 wt% solution,
IE becomes very low under shear even at low shear rate and rapidly decreases to zero with increasing shear rate. The transmitted light intensities
Ix (with crossed polarizers) and
I (with parallel polarizers) change with shear rate in a wave-like manner, indicating that the retardation changes continuously with increasing shear rate. From the results, it is concluded that in the case of the 10% solution the polydomain cholesteric structure in the undisturbed state changes easily to a continuous phase of nematic structure even at low shear rate. In the case of a 15 wt% solution,
IE decreases from a high value in the undisturbed state to a lower value by shearing and remains almost constant over a certain range of shear rate, until it suddenly decreases to zero at a certain high shear rate where the system changes into a continuous nematic phase. In the case of a 20 wt% solution,
IE remains at a rather high level even at high shear rate, indicating that the system undergoes polydomain flow. In the case of a 40 wt% solution,
IE remains at a high value even at the highest shear rate examined, and the system is considered to flow maintaining a polydomain cholesteric structure. No large scale orientation of molecules is observed even at high shear rate. The apparent viscosity of the solutions is the lowest among the solutions tested. It is pointed out that the lower viscosity does not always mean the higher degree of molecular orientation.
The recovery of
IE, after cessation of the steady shear, is negligibly small, if the steady state
IE has once reached nearly zero. However, the recovery of
IE is quite large, when the steady state
IEll has remained at a high value and the system has held its polydomain structure in flow.
抄録全体を表示