Friction in (Im-) Miscible Polymer Brush Systems and the Role of Transverse Polymer Tilting

It was found recently that two polymer brushes in a tribological contact do not interdigitate when each polymer brush has its own preferred solvent, leading to low friction and low wear rates. Here, we demonstrate, using molecular dynamics simulations, that mutually miscible and fully solvated brush systems do not significantly overlap either if the radii of curvature of the surfaces, to which the brushes are grafted, are sufficiently small. The brushes achieve this by bending away from the center of the contact, while they bend toward the center of the capillary when being only partially solvated. For the fully solvated brushes, immiscible systems also show smaller friction than miscible systems, although the friction reduction is less than for partially solvated brushes