Regensburg 2010 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 21: Soft Matter II

DY 21.2: Talk

Wednesday, March 24, 2010, 16:45–17:00, H47

A Gibbs free energy model for compressible polymer blends. Application for describing diffusion in compressible multi-components systems — •Elian Masnada and Didier R. Long — CNRS/Rhodia UMR5268 Lyon (France)

We propose a Gibbs free energy model for describing the thermodynamics of compressible polymer blends, or polymer-solvent systems. Most of such models require the introduction of ad-hoc equation of state relations for each component, as well as an ad-hoc equation of state for the blend. The model we propose is self-contained in the sense that we derive the equation of state of the blends, and that the latter gives the equation of state of the pure liquid in the case when the other component is absent. We show how we can compare the predictions of our model to experimental data such as the predictions of spinodal lines, or the calculation of an effective Flory interaction parameter which can be compared to experimental data. We show how our model allows for recovering the usual expression of the RPA (structure factor) of incompressible polymer blends, in the limit of large bulk modulus K (as compared to the osmotic modulus). Our model allows for calulating the effect of the pressure on the compatibility of polymer blends, either in the case of low temperature spinodal decomposition (UCST) or in the case of high temperature decomposition (LCST). Our model contains a smaller number of adjustable parameters than previously published models, which all have a physical meaning. We will also discuss how this free energy model can be used for describing the diffusion of various species in out of equilibrium situations.