PBLG濃厚溶液の流動光学的研究[I]

測定装置の試作および等方性溶液の挙動

抄録

A new apparatus has been designed for study on rheo-optical properties of liquids and liquid crystals. A usual cone and plate type rheometer, equipped with a transparent cone and plate made of quartz is combined with an optical system: A monochromatic laser light beam is introduced successively to a polarizer, a quartz plate, a sample, a quartz cone, and an analyzer, and finally the transmitted light is detected by a photomultiplier tube. Thus the optical system enables us to measure the transmitted light intensities of polarized light through the sample under shear deformation.
Measurements have been performed on solutions of poly (γ-benzyl glutamate) in m-cresol of concentrations below A-point (i.e., in isotropic state) at room temperature (20°C). The shear stress and the transmitted light intensities (I_×, I_″, and I_E) have been measured simultaneously as a functions of steady shear rate (2×10^-2~10²s^-1), where I_×, I_″, and I_E are, respectively, the transmitted light intensities under crossed polarizers, under parallel polarizers, and under crossed polarizers at extinction position. At high shear rates, quantities I_″ and I_E vary in a wavelike manner with alternating maxima and minima with increasing shear rate. However, the quantities I_×+I_″ and I_E are independent of shear rate. Thus the variation of I_× and I_″ is considered to arise from the continuous retardation change of the system with increasing shear rate, due to the increase in orientation of the rod-like macromolecules. The change of I_× or I_″ begins to be remarkable at a certain critical shear stress, where the viscosity begins to decrease noticeably with increasing shear rate. The critical shear stress was independent of the concentration. The birefringence of the system under. shear is also evaluated from the I_× and I_″ data in terms of socalled transmission method.