The Dynamics of Polymer Liquid Crystals

This brief account of past investigations is concerned with work on polymer liquid crystals (PLCs), where the majority of work has considered nematic materials. Among the unique rheological responses associated with PLCs are 

The first normal stress difference is observed to change sign from positive, to negative, and back to positive as the shear rate is increased [159,160] 

Transient shear stresses following either a flow reversal or a step-up in shear rate show pronounced oscillations, and the period of these oscillations scales with the shear rate [161]. 

Recoverable shear strain measurements following the removal of shear stress after the sample has been sheared at a rate y0 collapse onto a single curve when the data are plotted against y0r [162], 

The molecular theory of Doi [63,166] has been successfully applied to the description of many nonlinear rheological phenomena in PLCs. This theory assumes an un-textured monodomain and describes the molecular scale orientation of rigid rod molecules subject to the combined influence of hydrodynamic and Brownian torques, along with a potential of interaction (a Maier-Saupe potential is used) to account for the tendency for nematic alignment of the molecules. This theory is able to predict shear thinning viscosity, as well as predictions of the Leslie viscosity coefficients used in the LE theory. The original calculations by Doi for this model employed a preaveraging approximation that was later 

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