Structure of linear polymeric chains confined between impenetrable spherical walls

Abstract

The bond-scale and chain-scale structure of linear polymers located close to spherical impenetrable surfaces is studied in dense systems by means of lattice Monte Carlo simulations. The role of the various types of interactions (entropic, cohesive in the bulk polymer, attraction to filler surface) and that of the chain length, polymer density, and wall curvature in defining the polymer structure is analyzed. The size effect of the spherical fillers is investigated by scaling the filler radius at constant filler volume fraction. On the bond scale, the chain ends segregate to the wall in all systems, with the effect being essentially independent of wall curvature. The bonds are preferentially oriented in the direction tangential to the wall. The distance from the wall over which these effects are observed is about one bond length in the athermal case and about two chain gyration radii in the energetic case. On the chain scale, the ellipsoidal chains undergo a “docking” transition to the spherical fillers. The ellipsoids do not deform, rather rotate with their large semiaxis in the direction tangential to the filler as their centers of mass approach the wall. This configurational entropy-controlled situation remains valid when cohesive interactions are considered in the bulk polymer and even with a hydrogen bond strong attraction of the polymer to the wall. When the wall-to-wall distance between fillers decreases below two bulk gyration radii, the chain size decreases in the direction of its large semiaxis, an effect essentially independent of the details of the energetic interactions in the system.