SORPTION OF ORGANIC-SOLVENTS INTO DENSE SILICONE MEMBRANES .2. DEVELOPMENT OF A NEW APPROACH BASED ON A CLUSTERING HYPOTHESIS FOR ASSOCIATED SOLVENTS

The difficulties encountered in fitting sorption isotherms of associated liquids (alcohols, ketones) in poly-dimethylsiloxane (PDMS) by Flory-Huggins and related theories have been reported in a previous work; cluster formation, expected to explain these deviations, has been examined according to various approaches already reported to take into account such a phenomenon (polycondensation in an inert matrix, dimer formation). Given the poor results obtained by these approaches, a new equation, based on elementary affinity constants between polymer and sorbed solvent species in a lattice graph has been tested. Results obtained by fitting the resulting two-parameter equation to alcohol-PDMS results show the ability of the proposed equation to fit precisely the isotherms. Furthermore, pictures of the polymer-solvent lattice can be easily obtained by this approach, by computer simulation. Generalizations of the novel approach to other polymer solvent systems as well as to multicomponent systems are discussed. Diffusion studies on the basis of this heterogeneous matrix picture could possibly be undertaken later.