Modeling the interactions between polymers and clay surfaces through self-consistent field theory

Using numerical self-consistent field (SCF) calculations, we investigate the interactions between two closely spaced surfaces and the surrounding polymer melt. Short chains (surfactants) are terminally anchored to each of the surfaces. The coated substrates model organically modified clay crystallites (sheets). Through the calculations, we vary the characteristics of the surfactants and polymers to isolate conditions that drive the polymer to penetrate the gap between the surfaces. We also consider the effect of employing end-functionalized chains to promote the dispersion of bare clay sheets within the polymer matrix. We find that this scheme provides a robust method for exfoliating the sheets. To consider this case in greater depth, we develop an analytical SCF theory to model the interactions among the functionalized chains, nonfunctionalized polymers, and the clay sheets. The results from the numerical and analytical SCF models show good agreement on the behavior of the system. The results indicate that the optimal polymeric candidates for creating stable exfoliated composites are those that would constitute optimal steric stabilizers for colloidal suspensions.