Rod-like polymers in concentrated solutions

The theory predicts two relaxation processes for monodisperse rods a fast one associated with the wobbling of a rod in the cage, and a slow one associated with the overall reorientation of the rod. The fraction of the mean square dipole moments relaxed in the former process should be of the order of 2AQ and the relaxation time should be much shorter than that characteristic of the unrestricted diffusion 

It should be noted that the two-step rotational dynamics of the long axis in a semidilute solution qualitatively resembles the jS- and a-processes in the solid state of flexible polymers the short-timescale motion in the cage may be compared to the jS-process, the long-timescale fluctuations in the environment with the a-process. 

The fast and slow processes have been observed experimentally using Kerr eflFect measurements of PBLG solutions. However, since 2AQ is a very small quantity, the diffusion in the cage is undetectable by DR spectroscopy and only the slow process can be studied by this method. 

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Fig. 4.14. Typical concentration-temperature phase diagram for rod-like polymers in concentrated solution. Poly(n-hexyl isocyanate) (PHIC) in toluene. L and L.C. indicate isotropic and liquid-crystalline states of solution, respectively. ...

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... 

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