Self-Diffusion of Rodlike Polymers in Isotropic Solutions

Document Type

Article

Publication Date

11-1-1994

Abstract

The self-diffusion coefficient, Ds of fluorescently tagged poly(γ-benzyl α,l-glutamate) has been measured throughout the isotropic regime in pyridine. Intrinsic viscosity, phase boundary studies, epifluorescence microscopy, computer modeling, and the diffusion rates themselves show that the labeling does not appreciably perturb the semiflexible rod structure of the polymer. It is also demonstrated that pyridine is a good solvent for poly (γ-benzyl α,l-glutamate), comparable to N,N′-dimethylformamide. As concentration increases, two or three regimes are found depending on the rod length. Dilute behavior holds to number densities, v, well exceeding L-3, where L is the rod length. A somewhat better estimate of the point at which Ds begins to decrease is the classical criterion, c ≈ [η]-1 where c is the weight/volume concentration and [η] is the intrinsic viscosity. Over the whole range of molecular weights, the condition vdL2 ≈ 0.5–1, where d is the rod diameter, well describes the downturn number density. This corresponds to v/v* ≈ 0.1–0.2, where v* = 16/(πdL2) is the Onsager critical number density associated with the lyotropic liquid crystal transition. Once diffusion begins to decrease, it does so strongly, obeying Ds ~ c-1.13±0.04L-1.8±0.2. The third regime of diffusion, evident only in the two longest samples, is again relatively level and lasts to the lyotropic transition. Diffusion does not cease at any concentration, and Ds is reasonably well scaled when number density is normalized by v*, which underscores the importance of finite thickness effects for semidilute solutions of poly(γ-benzyl α,l-glutamate). The self-friction and mutual friction coefficients differ, with the former being lower in dilute solutions. © 1994, American Chemical Society. All rights reserved.

Publication Source (Journal or Book title)

Macromolecules

First Page

6871

Last Page

6882

This document is currently not available here.

Share

COinS