Adhesion of polycarbonate blends on a nickel surface

We demonstrate that the adhesive behavior of a phenol-terminated bisphenol A polycarbonate melt to a (111) nickel surface changes significantly if a small amount of short chains is present, i.e., in polydispersed melts or self-blends. Attractive interaction of the chain ends with the surface results in an adsorbed layer, made of single- and two-end attached chains. Short chains, however, diffuse from the bulk and occupy the adsorption sites much faster than the long ones. Interplay between the surface concentration of short chains, their molecular conformation, and excluded volume results in a nonmonotonic dependence of the surface coverage by long chains on the molecular weight of the additive. The smallest polycarbonate coverage is achieved for diphenyl carbonate due to its high mobility and relatively large excluded volume. We propose that self-blending can be used to modify, in a controlled fashion, the friction coefficient of a melt sheared past the nickel surface.