ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The sedimentation equilibrium of polymers in mixed solvents at infinite dilution of polymer was analyzed by thermodynamic methods equivalent to those used by Stockmayer and Kirkwood and Goldberg for the light scattering case. It was found that the apparent weight-average molecular weight in a binary solvent mixture (when nonrefractometric methods are used to measure the experimental concentration gradient) is formally identical with that derived by Lansing and Kraemer on the assumption of stoichiometric combination of one of the solvents with the polymer. The “solvation number” now actually measures a preference for one solvent and can be expressed in terms of thermodynamic quantities characteristic of the ternary polymer-solvent system. In the case of refractometric measurements, where the two solvents have different refractive indices, refraction terms similar to those encountered in light scattering theory for mixed solvents also enter. Under equilibrium conditions, for polymer solutions in pure solvents, thermodynamics can say nothing about “solvation,” which is inseparable from the over-all nonideal behavior at finite concentrations. There is strong reason to believe that all types of experiments designed to measure solvation in mixed solvents under equilibrium conditions must give the same answer, since the same thermodynamic quantities determine polymer-solvent interactions in all cases. By assuming a dynamic equilibrium between sedimentation and diffusion in the equilibrium case and using the sedimentation term for the sedimentation velocity case, an expression for the sedimentation constant in mixed solvents at infinite dilution of polymer has been obtained. This expression is almost the same as that previously derived by Schachman and Lauffer, the difference occurring in an assumption about the density of solvated liquid made by these authors.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1952.120080501
