Molecular engineering of graft and matrix polymers for tuning grafted particle dispersion in polymer nanocomposites: A theory and simulation study*

In polymer nanocomposites (PNCs) comprised of grafted nanoparticles in a polymer matrix, tailoring the graft and matrix polymers is a way to tune the effective inter-particle interactions and morphology. In this talk we present our work using molecular simulations and theory showing how increasingly attractive graft-matrix interactions affect the interpenetration of matrix and graft chains (termed as grafted layer wetting) and the dispersion/aggregation of grafted particles in the matrix. Past work by our group on similar systems has shown that wetting/dewetting and dispersion/aggregation are two distinct phase transitions, former a continuous one and the latter a first-order transition as a function of graft-matrix interactions. In this work we find that as the graft-matrix attraction increases, the graft chains extend and matrix chains increasingly wet the grafted layer, leading to larger and harder grafted particles compared to analogous PNCs with athermal graft-matrix interactions. Simultaneously, the PNC structure changes from an aggregated/dispersed morphology dictated by the entropic limit to a dispersed morphology due to favorable weak graft-matrix attraction, and finally, to a correlated fluid of hard grafted particles at stronger graft-matrix attraction