Densely packed semiflexible macromolecules in a rigid spherical capsule

Abstract

The ordering of semiflexible polymers with persistence length lp and contour length L confined in a sphere of radius R is studied by molecular dynamics simulations of a coarse-grained model. Monomer densities are chosen where the corresponding bulk lyotropic solution or melt is a well-ordered nematic, and purely repulsive walls of the rigid confining sphere are considered. It is found that polymers close to the walls are bent according to the curvature of the confining spheres with all their monomers in a few layers parallel to the sphere surface, whereas the remaining macromolecules closer to the sphere center have one chain end and their center of mass far from the surface. The latter chains are responsible for the average nematic order of the system for sufficiently stiff chains. If L exceeds R, a single transition from isotropic to nematic states is found when lp increases. However, if R is close to an even multiple of L, a second transition occurs where chain ends are enriched near the equatorial plane (and two further planes parallel to it, if R 2L); i.e., the system develops a distorted smectic structure. The order in the surface shell then is characterized by topological defects.