Dissipative Particle Dynamics Simulations of Grafted Polymer Chains between Two Walls

We have used the dissipative particle dynamics method (DPD) to simulate grafted polymer brushes in a pore geometry using two walls of tethered DPD particles to form the top and bottom boundaries of the simulation cell. The polymer density profiles show a parabolic shape in agreement with the SCF theory for brushes in a good solvent. At fixed wall separation and chain length, the overlap of the brushes increases with increasing surface coverage. The widths of the polymer brushes decrease significantly with decreasing surface coverage, and the effects are more dramatic for the longer chains. The diffusion along the pore axis is significantly greater for the solvent particles in the middle of the slab than for those in the polymer/wall region since the solvent molecules are trapped in the entangled polymer. Calculation of the average asphericity parameters from the inertia tensor of the polymers demonstrates that the chains stretch with increasing coverage. As the chains become longer, the degree of ordering with respect to the layer normal increases at a given surface density. The ordering with respect to the surface normal decreases with decreasing coverage at fixed chain length. The director of the layer is close to the layer normal.