Molecular Simulation Study of the Structure of High Density Polymer Brushes in Good Solvent

Molecular dynamics simulations are presented of coarse-grained, polar, polymer brushes in a good polar solvent at high grafting densities. Chain extension is heavily influenced by temperature, stretching far from the surface at high temperature (350 K) while weak absorption and loop formation is observed at low temperature (300 K). Simulations of isolated free chains of different lengths in solution demonstrate the polymers are in good solvent conditions at both temperatures. Consistent with previous findings, increasing grafting density leads to larger chain extension under all conditions. A saturation limit at about half the bulk polymer density is found for high chain length and grafting density. Even at very high grafting densities a polymer depletion region near the surface is observed at 350 K due to an orthogonal orientation of the chain at the grafting surface. Radial distribution functions reveal that the grafting pattern does not affect the overall brush configuration beyond the first five monomers of each chain as long as the surface is homogeneously covered.