Coarse-grained simulations of pairs of polymer-grafted nanoparticles in implicit solvent

By grafting polymer chains to nanoparticles, one can create inorganic-organic hybrid materials whose structure and properties can be tuned by controlling graft density, chain length, and other molecular features. These polymer-grafted nanoparticles (PGNs) are usually synthesized and processed in solution, and then are often deposited and dried to create films or bulk materials with uniform spacings of particles in a mechanically robust matrix. Understanding interparticle interactions in solvated PGN systems is crucial to controlling the structure and properties of PGNs during and after deposition. Here, we use molecular dynamics simulations with a generic coarse-grained model to study polymer conformations and effective interparticle interactions of PGN systems in implicit solvent, for systems at two graft densities and a range of solvent strengths. As expected, higher graft density and good solvent correspond to more extended graft chain conformations, which are analyzed via mean-squared internal distances. We calculate the potentials of mean force between pairs of PGNs and find a relatively sudden onset of a deep attractive well with increasing solvent strength, which occurs at nearly the same solvent strength regardless of graft density. The implications of our results for solution phase behavior are discussed.