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 associat ed liquids (alcohols, ketones) in poly-dimethylsiloxane (PDMS) by Flor y-Huggins and related theories have been reported in a previous work; cluster formation, expected to explain these deviations, has been exam ined according to various approaches already reported to take into acc ount such a phenomenon (polycondensation in an inert matrix, dimer for mation). Given the poor results obtained by these approaches, a new eq uation, based on elementary affinity constants between polymer and sor bed solvent species in a lattice graph has been tested. Results obtain ed by fitting the resulting two-parameter equation to alcohol-PDMS res ults show the ability of the proposed equation to fit precisely the is otherms. Furthermore, pictures of the polymer-solvent lattice can be e asily obtained by this approach, by computer simulation. Generalizatio ns of the novel approach to other polymer solvent systems as well as t o multicomponent systems are discussed. Diffusion studies on the basis of this heterogeneous matrix picture could possibly be undertaken lat er.