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COUPLING OF MOLECULAR DIFFUSION AND POLYMER RELAXATION IN POLYMER-SOLVENT SYSTEMS (DEBORAH NUMBER, FREE-VOLUME THEORY).

Author
NI, LONG-WEN
Physical Description
91 pages
Additional Creators
Pennsylvania State University
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Summary
An oscillatory diffusion experiment has been developed for the accurate determination of the diffusivity and thermodynamic data for liquid solvents in amorphous polymers, such as the polyvinylacetate-chloroform system, and the polyvinylacetate-water system. The experiment is based on the response from a sample weight of polymer which is exposed to a sinusoidal solvent vapor pressure.
The diffusion coefficient is computed from the phase angle between the pressure function and weight function from periodic steady-state data. Furthermore, theoretically, it can also be calculated from the transient state, which is before the periodic steady state. Diffusivity and solubility data for polyvinylacetate-chloroform are presented. The effects of the concentration dependence of diffusion coefficients and a diffusion Deborah number are examined in this system.
The apparatus, which consists of a Cahn electronbalance, a solvent supply and a microcomputer, can be used not only for the collection of diffusion data but also for the study of the molecular diffusion and polymer relaxation effects in the polymer-solvent system. In the polyvinylacetate-water system, the anomalous behavior occurs; the diffusion coefficient is decreased when the oscillatory cycle time is increased. Up to now, no adequate explanation has been found.
The free-volume theory for diffusion in polymer-solvent systems proposed by Vrentas and Duda can predict the shapes of the curves of self-diffusion which are similar to the experimental data by Tanner. An explanation is proposed by considering the effect of concentration on both the free volume and the entanglement density in the polymer-solvent mixture for the experimental concentration behavior by Tanner. The random motion of expanded polymer chains is treated by using the free-volume theory of transport. The effect of polymer molecular weight on the concentration dependence of the polymer self-diffusion is studied. The free-volume analysis predicts that (PAR-DIFF)lnD(,2)/(PAR-DIFF)(omega)(,1) > 0 and (PAR-DIFF)('2)lnD(,2)/(PAR-DIFF)(omega)(,1)('2) > 0 for high solvent concentration in the limit of high polymer molecular weight, where (omega)(,1) is the solvent mass fraction and D(,2) is the polymer self-diffusion coefficient.
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Dissertation Note
Ph.D. The Pennsylvania State University 1984.
Note
Source: Dissertation Abstracts International, Volume: 45-06, Section: B, page: 1854.
Part Of
Dissertation Abstracts International
45-06B
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