Mutual diffusion in polymer solutions: Spanning phase diagrams

Published Date
Polymer
5 August 2016, Vol.97:472–479, doi:10.1016/j.polymer.2016.05.061

• Author 

• S. Shams Es-haghi
• M. Cakmak ^,

• Department of Polymer Engineering, 250 S. Forge St., The University of Akron, Akron, OH, 44325-0301, USA

Received 8 December 2015. Revised 9 May 2016. Accepted 21 May 2016. Available online 24 May 2016. 

Highlights

• •
  An equation for mutual diffusion coefficient in polymer solutions was derived using Onsager’s variational principle.
• •
  The trend of variation of mutual diffusion coefficient was studied in different hypothetical phase diagrams.
• •
  It was shown that cessation of diffusion occurs on the spinodal line in all of the phase diagrams.
• •
  It was shown that diffusion slows down by approaching the critical point and, in general, the spinodal line.

Abstract

This paper aims to discuss the trend of variation of mutual diffusion coefficient in polymer solutions exhibiting different phase behavior. An equation for mutual diffusion coefficient in polymer solutions was derived in the framework of classical irreversible thermodynamics using Onsager’s variational principle. The behavior of mutual diffusion coefficient in different phase diagrams was investigated by changing the Flory-Huggins interaction parameter to include concentration and temperature dependencies using Koningsveld interaction factor. The proposed diffusion coefficient satisfies the asymptotic behavior at infinite dilution, becomes zero on the spinodal line and changes sign at the onset of entering the unstable zone of phase diagrams. It was shown that the diffusion slows down near the critical point and in general by approaching the spinodal curve. Moreover, it was shown that the derived equation for mutual diffusion coefficient can be expressed in terms of osmotic bulk modulus which is consistent with the result of a variational approach using Landau-Ginsberg-Wilson Hamiltonian.

Graphical abstract

Keywords

• Mutual diffusion
• Phase diagram
• Polymer solution

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• ∗ 
  Corresponding author.

© 2016 Elsevier Ltd. All rights reserved.

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