EFFECT OF TEMPERATURE ON THE RHEOLOGY OF POLYMERIC LIQUID CRYSTALS

As part of a more general effort to elucidate the flow of polymeric liquid crystals, the effect of temperature on the rheological properties has been investigated. A lyotropic sample of poly(γ-benzyl-L-glutamate) in m-cresol has been used throughout the measurements. Under steady state shear flow the viscosity and the first normal stress difference have been measured. Oscillatory flow after cessation of steady shear flow reveals a time effect which led to the determination of initial and final moduli; both have been measured as a function of temperature. Finally some transients have been considered as well.

The limiting zero frequency value of the dynamic viscosity and the zero shear value of the steady state viscosity have different activation energies. The dynamic moduli can be scaled for temperature effects by means of the zero frequency viscosity. Because of the difference in activation energies this scaling does not hold for the steady state properties. An alternative scaling procedure is suggested. The time scale of the transients is nearly independent of temperature. None of the available theoretical models describes the measured phenomena.