THE ENGAGED SPECIES INDUCED CLUSTERING (ENSIC) MODEL - A UNIFIED MECHANISTIC APPROACH OF SORPTION PHENOMENA IN POLYMERS

The description of sorption equilibria of solvents in polymers is a ke y problem which has to be solved in order to achieve a correct underst anding of transport processes through dense membranes. Up to now, this purpose is limited essentially to solvents in elastomers, which are d escribed by Flory-Huggins thermodynamics theory, while sorption of gas es in glassy polymers is usually based on a mechanistic one, the so-ca lled dual mode model. Given the difficulties encountered as soon as po lymer solvent peculiarities (non-regular mixing enthalpy, network elas tic contribution) are taken into account, other types of mixtures can hardly be described by purely thermodynamic models unless complicated expressions are used. A simple mechanistic approach has been developed in order to circumvent these limitations; it is based on the assumpti on that insertion of a solvent molecule into the polymer solvent matri x will be governed by the intrinsic affinity of the solvent for either a polymer segment or an already sorbed solvent molecule. The model en abling cluster formation description has been named engaged species in duced clustering (ENSIC). A series of data related to the most frequen tly used polymer dense membrane materials have been used in order to c heck the fitting efficiency of the newly developed expression; it is s hown to give a very good description of sorption isotherms of many bin ary polymer solvent systems, including polar and apolar c:ompounds, in either elastomeric, glassy or thermoplastic membrane materials. The p hysico-chemical interpretation of the two probabilistic insertion para meters used in the ENSIC model, as well as prospects concerning the ex tension to multicomponent systems or transport mechanisms simulations are discussed.