Morphology Control of Hairy Nanopores

Abstract

The properties of polymer layers end-grafted to the inner surface of nanopores connected to solvent reservoirs are studied theoretically as a function of solvent quality and pore geometry. Our systematic study reveals that nanoconfinement is affected by both pore radius and length and that the conformations of the polymer chains strongly depend on their grafting position along the nanopore and on the quality of the solvent. In poor solvent, polymer chains can collapse to the walls, form a compact plug in the pore, or self-assemble into domains of different shape due to microphase separation. The morphology of these domains (aggregates on pore walls or stacked micelles along the pore axis) is mainly determined by the relationship between chain length and pore radius. In other cases the number of aggregates depends on pore length. The presence of reservoirs decreases confinement at pore edges due to the changes in available volume and introduces new organization strategies not available for infinite nanochannels. In good solvent conditions, chains grafted at the pore entrances stretch out of the pore, relieving the internal osmotic pressure and increasing the entropy of the polymers. Our study also addresses the experimentally relevant case of end-grafted chains on the outer walls of the membrane surrounding the nanopore. The effect of these polymer chains on the organization within the nanopore depends on solvent quality. For good solvents the outer chains increase the confinement of the chains at the entrance of the pore; however, the effect does not result in new structures. For poor solvents the presence of the outer polymer layer may lead to changes in the morphology of the microphase-separated domains. Our results show the complex interplay between the different interactions in a confined environment and the need to develop theoretical and experimental tools for their study.