Semiflexible Polymers in Spherical Confinement

Semiflexible macromolecules find various applications as versatile materials, in particular due to their possible liquid crystalline order, and are also important constituents of living matter. We studied the ordering of such stiff macromolecules confined in spheres by molecular dynamics simulations, and found that densely packed semiflexible polymers cannot exhibit uniform nematic order when their contour length is of the same order as the sphere radius. Instead, the confinement leads to the emergence of topological defects on the sphere surface with competing ordering in the interior of the sphere. Each of the configuration variables including chain length, chain stiffness, packing density, and shell thickness uniquely affect the ordering, including the nature and relative orientation of the defects on the surface. For example, at high densities, a thin shell of polymers close to the surface exhibits a quadrupolar tennis ball texture due to the confinement-induced gradual bending of polymer bonds. Systemic trends observed could pave the way for better understanding the links between topological defects and elastic properties of polymers. Further, controlling the defect locations is promising for designing patterned colloids in experiments by functionalizing defect sites.