Molecular dynamics simulations of nanocomposites based on poly(epsilon-caprolactone) grafted on montmorillonite clay

Intercalated and exfoliated models of polymer nanocomposites based on poly(epsilon-caprolactone) and functionalized montmorillonite clay are studied by means of molecular dynamics simulations. Intercalated and exfoliated models are considered for probing the structural characteristics of the corresponding nanocomposites prepared by melt intercalation and in situ polymerization, respectively. In the exfoliated system, the organization of the polymer chains onto the clay surface is examined in terms of the density profiles and the order parameter function. A layered structure can clearly be seen to form near the surface with density maxima higher than in amorphous poly(epsilon-caprolactone). This can be viewed as an increase in effective particle thickness, which can contribute to the outstanding gas barrier properties of the exfoliated nanocomposites. The comparison of the structures and energetics of the intercalated model with those of a nanocomposite model based on a nonfunctionalized clay indicates nearly similar characteristics. Nevertheless, the slight differences observed for the interfacial polymer density and clay- and surfactant-polymer binding energies can account for the differences in rheological measurements. The results also suggest that the difference in morphology obtained for the nanocomposites prepared by the two synthetic approaches can be ascribed to both a difference in interfacial polymer density and the formation of bridging polymer chain structures that hinder the exfoliation process.