Mechanism of exfoliation of nanoclay particles in epoxy-clay nanocomposites

The mechanism of nanoclay exfoliation was investigated in epoxy-clay nanocomposites system. The elastic force exerted by cross-linked epoxy molecules inside the clay galleries was found responsible for exfoliation of clay layers from the intercalated tactoids. Complete exfoliation of clay galleries was observed under the conditions of slow increase of complex viscosity and fast rise of storage modulus. It was observed that faster intragallery polymerization, though expedited the exfoliation process, was not necessary for exfoliation. It was also observed that clays containing hydroxylated quaternary ammonium ions and quaternary ammonium ions with no polar functional groups produced exfoliated structures equally easily, provided the ratio of storage modulus to complex viscosity was maintained above 2-4 1/s. Both higher curing temperature and the presence of organically modified clay particles accelerated the formation of gels, and the gel time presented an upper bound of time available for exfoliation.