Mean-Field Model of the Collapse Transition of Brushes inside Cylindrical Nanopores

We analyze the mean-field theory of polymer brushes inside cylindrical channels to predict the properties of the collapse transitions of the brush, related with an opening of the channel, upon changes of the solvent quality. The interplay of compressibility of the polymer brush under poor solvent conditions and the surface tension due to opening of a central void in the channel lead to a discontinuous phase transition, which is characterized by a bi-stable free energy landscape. Our model can be extended to describe copolymer brushes with modified end-groups. The different solubility properties of the two monomer species can be used to tune the thermal response of the brush-decorated pore. Molecular dynamics simulations are carried out to quantitatively test the mean-field approach. In particular, it is demonstrated that, within a certain parameter range, copolymer brushes exhibit a lower critical transition temperature, that is, lead to an opening of the pore by increasing the temperature. The simulations quantitatively confirm essential predictions of the mean-field model such as the impact of the degree of polymerization, the radius of the nanopore, and size or interactions of the end-groups.