Physicochemical driving forces behind exfoliation process of a synthetic montmorillonite in PDMS polymers

The conditions under which exfoliation of organo-montmorillonite in Poly(dimethylsiloxane) elastomers may occur were investigated via a three approaches: determination of the inter-platelet distance (as measured by WAXS), the surface energy evaluation (via inverse gas chromatography) of the polymer matrix and the clays, and measurement of heat of interaction (using a flow microcalorimeter in heptane) between polymers and the clay. The exfoliation efficiency is estimated by performing dynamic mechanical measurements. The results indicate that compatibilization and geometrical considerations are not sufficient requirements to transform clay particles into platelets. It evidences the determinant role of specific interactions between the reactive polymer end-groups and the filler surface. Polymer conformation on the clay surface and heat of adsorption associating “dispersive or London” forces and hydrogen bonding of respectively trimethyl- and hydroxyl-terminated polymer are evaluated.