Elastic Recovery After Steady Shearing of PBLG Liquid Crystal Polymers.

Recoverable strain measurements on liquid crystalline PBLG [poly(gamma-benzyl-L-glutamente)] show no regime of linear viscoelasticity where the recovery is proportional to prior shear rate gamma sub o even at rates low enough that the viscosity is nearly independent of gamma sub o. Instead, the total strain recovery is independent of gamma sub o, although the time over which this recovery occurs is inversely proportional to gamma sub o. Plots of recoverable strain versus the product of time t and gamma sub o for various values of gamma sub o nearly superpose. This scaling with gamma sub o sup (-1) is similar to a result obtained with PBLG by Moldenaers and Mewis and confirmed here in measurements of G' and G" after cessation of steady-state shearing. Visual observation of the material under a polarizing microscope after cessation under shear suggests that these peculiar results are caused by the evolution of the pattern of defects or texture of the material after sharing.