Low‐frequency and high‐frequency relaxations in dynamic electric birefringence of poly(γ‐benzyl‐L‐glutamate) in m‐cresol

Abstract

The dc component Δn of the electric birefringence of poly(γ‐benzyl‐L‐glutamate) in m‐cresol is measured under an ac electric field at frequencies from 0.5 Hz to 200 kHz for solutions covering the dilute and semidilute regions. The dispersion curve indicates that at low frequencies Δn decreases with increasing frequency (low‐frequency relaxation). For high‐molecular‐weight polymers at high concentration, Δn becomes negative at high frequency and its absolute value decreases with further increase in frequency (high‐frequency relaxation). A unified theory for the two relaxations is developed on the basis of a model in which, in the semidilute regime, the rodlike polymer is confined in a cage formed by neighboring polymers and the lifetime of the cage lies between relaxation times of the two relaxations. The low‐frequency relaxation is ascribed to end‐over‐end rotation of the polymer and the high‐frequency relaxation to the rotation within a limited angle in the cage. The dependences of relaxation parameters on polymer concentration and molecular weight are reasonably explained by the theory.

Dynamics of Hairy-Rod Polymers: Semidilute Regime

“…We should only mention that even for such systems the rate is not expected to follow the c -2 behavior of the Doi-Edwards model in the whole semidilute and concentrated regime, but rather a weaker c dependence (c -1 ) at low concentrations, and only for highly entangled solutions is the DE behavior reached. 14,18,22 …”

“…While the rotational diffusion coefficient, D r , initially predicted from the DE model 1 for rods in the semidilute region, was to exhibit a strong c dependence (D r /D r,0 ∼ c -2 ), it is now evident, from both experimental studies 11,14,18 and other theoretical models and simulations, 21,15,22 that a rather weaker c dependence is followed until, only at high concentrations, the DE prediction is reached. These theories involve recalculation of the cage size 15 or consideration of dynamic distortion of cages and finite thickness effects.…”

Particle shape and suspension rheology of short-fiber systems

“…the fiber can freely rotate in arbitrary directions. According to some authors, 26,27 this estimate is too strictly limiting. Instead of the volume fraction occurring in Eq.…”

Self‐Assembly and Dynamics of Polypeptides

“…[46][47][48] These studies revealed a strong process, which was attributed to the rotation of the a-helix as a rigid rod. The relaxation times had a t $ M 3 molecular weight dependence, which is consistent with the rigid rod model.…”