Impact of Hydrogen Bonding Interactions on Graft–Matrix Wetting and Structure in Polymer Nanocomposites

We present a new coarse-grained (CG) model that captures directional interactions between graft and matrix polymer chains in polymer nanocomposites (PNCs) comprising polymer grafted spherical nanoparticles in a matrix polymer. In this CG model we incorporate acceptor and donor CG beads along with graft and matrix monomer CG beads and optimize the bonded and nonbonded interactions to mimic directional and specific H-bonding between the acceptor and donor sites on graft and matrix chains, respectively. Using this CG model and molecular dynamics simulations we show that H-bonding interactions between graft and matrix polymer chains increase the grafted layer wetting by matrix chains compared to that at the purely entropic limit. One can achieve equivalent grafted layer wetting in PNCs with directional acceptor–donor interactions and PNCs with isotropic graft–matrix interactions, but the directional acceptor–donor interaction strength needs to be much stronger than the isotropic graft–matrix monomer attraction strength. Strikingly, despite equivalent grafted layer wetting and graft chain conformations, on average, each graft chain interacts with fewer matrix chains and has a lower free volume in PNCs with H-bonding interaction as compared to PNCs with isotropic graft-matrix attraction. These trends are seen both at high (brush-like) and low grafting densities, and in PNCs with equal graft and matrix chain lengths as well as PNCs with matrix chain length three times the graft chain length.