Flow behavior of lyotropic solutions

Rheological properties under steady state and oscillatory shear flow of isotropic and nematic solutions of PpPTA, PBT and PBO were studied by Baird and Berry et alP Baird observed shear thinning for a series of PpPTA solutions in sulfuric acid (4-15 /o). These results also suggest that at higher shear rates very little difference exists between the anisotropic and isotropic phases. Steady-state viscosities as a function of the temperature observed for solutions of PBO in methanesulfonic acid 

Shear flow-induced birefringence measurements of an isotropic solution of PpPTA in concentrated sulfuric acid with a clearing point of 45°C were also performed by Picken. As shown in Fig. 6.5, the flow-induced birefringence increases strongly when the isotropic-nematic transition is approached. The results demonstrate that the application of a relatively small shear rate already leads to a degree of orientational order in the initially isotropic solution that is comparable with the order in the nematic phase. This points to a strong coupling between the orientation and the external flow field, and to the occurrence of a shear-induced phase transition. 

The texture during flow shows a rather grainy structure giving the impression of small domains tumbling over each other. The apparent size of the domains decreases with increasing shear rate. After cessation of flow, a banded texture is formed with the bands oriented normal to the shear direction. 

In a molecular theory describing the dynamics of rod-like polymers in concentrated solutions, Doi predicted an increase of the order parameter with a shear flow gradient. There have been several theoretical studies which predict that an elongational flow gradient also increases the order parameter substantially. Marucci and Ciferri found, however, that the largest contribution to the order parameter should arise from an increase 

In two supplementary studies applying X-ray and light-scattering techniques it was found that the transient behavior is governed by the 

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