Diffusion and viscosity measurements on macromolecules in solution

Abstract

In a previous paper we gave evidence for the validity of the Einstein‐Stokes law for determining molecular dimensions from the diffusion coefficient. In this work, we report on measurements on some polyoxyethylenes in water and on low molecular weight polystyrenes in benzene. The possibility of obtaining exact information regarding the molecular dimensions and the interactions with the solvent have been stated. In high polymers, the dimensions are considerably influenced by the molecular expansion coefficient, α; as a result of this, in studying structural properties of the molecules in solution, the measurements must be carried out in ideal solvents. We have developed a method based on viscometric measurements, which makes possible determination of the composition of the ideal mixture for a given temperature, where such a mixture consists of two components, of which one is a good solvent, and the other is a precipitating agent (non‐solvent). Such measurements have been made on 11 fractions of polystyrene from which it has been possible to determine the expansion coefficient α and the dimensions of the unperturbed molecules at 34°C.

Sensing a Self-Assembled Protein Structure through Its Permeation by a Ferrocene Labeled Poly(ethylene glycol) Chain

“…8 It was shown that for poly(ethylene glycol) chains of various molar weights the hydrodynamic radii derived from diffusion coefficients do not differ significantly from the radii of gyration. 9 The hydrodynamic radius we determined above is indeed very close to the radius of gyration of a PEG chain of 3400 molar weight in pure water at 25 °C which is 2.08 nm. 10 The corresponding average of the end to end distance is R F ) 5 nm.…”

“…In solution, a polymer chain adopts a random coil conformation that can be characterized by its radius of gyration ( R G ) or its end to end distance, also called the Flory radius ( R F ), with R F = 2.45 R G . It was shown that for poly(ethylene glycol) chains of various molar weights the hydrodynamic radii derived from diffusion coefficients do not differ significantly from the radii of gyration . The hydrodynamic radius we determined above is indeed very close to the radius of gyration of a PEG chain of 3400 molar weight in pure water at 25 °C which is 2.08 nm …”