Modeling Pairs of Polymer-Grafted Nanoparticles (PGNs) in Solution to Determine their Phase Behavior*

By grafting polymer chains onto nanoparticles (creating PGNs), one can precisely control interparticle interactions. PGNs are typically synthesized and processed in solution before use in applications such as flexible electronics where a precise spacing of inorganic particles in a robust and flexible matrix is desirable. Understanding their solution properties is crucial to control their structure during deposition and drying. We use coarse-grained molecular dynamics (MD) simulations to study the effective interactions between two PGNs in implicit solvent. Specifically, we use a Kremer-Grest type of model for graft chains and spherical nanoparticles ten times the monomer size. Monomers interact via mixed Lennard-Jones potentials; the repulsive part is kept constant while an attractive part is added with adjustable strength to consider various solvent strengths. Nanoparticle interactions are of an integrated form as though they are composed of a uniform melt density of monomers. Our MD simulations produce potential of mean force (PMF) profiles that are used in Gibbs Ensemble Monte Carlo (GEMC) simulations to determine, for each solvent strength, whether phase separation occurs and, if so, the densities of the coexisting phases. Phase diagrams for solvated PGNs will be discussed.