Chemically Specific Multiscale Modeling of the Shear-Induced Exfoliation of Clay-Polymer Nanocomposites

We recently showed, using chemically specific modeling and simulation, how the process of intercalation of polymers within clay sheets occurs, transforming the large-scale materials properties by a specific set of spatial and temporal processes that can lead to exfoliation. Here, we use the same hierarchal multiscale modeling scheme to understand the processes that occur during the shear-induced processing of clay-polymer nanocomposites. For both hydrophobic polymers (polyethylene) and hydrophilic polymers (poly(ethylene glycol)), we used free-energy methods to identify the lowest-free-energy separation of the clay sheets; the polymer molecules spontaneously intercalate into the clay interlayer from the surrounding polymer melt. We apply shear forces to investigate exfoliation and find that while exfoliation is promoted by shearing, it is the surfactant molecules that play the dominant role in resisting it.