(331v) Polymer-Modified Opal Nanopores

The surface of nanopores in opal films, assembled from 205 nm silica spheres, was modified with poly(acrylamide), PAAm, and poly(N-isopropylacrylamide), PNIPAAm, brushes using surface-initiated atom transfer radical polymerization. The polymer thickness inside nanopores was controlled by polymerization time and was monitored by measuring the flux of redox species across the opal film using cyclic voltammetry. PAAm brush thickness increased in the course of 26 hours of polymerization in a logarithmic manner from 1.3 to 8.5 nm leading to nanopores as small as 7.5 nm. The diffusion through PNIPAAm-modified opal films was studied as a function of temperature and polymer brush thickness. Nanopores modified with a thin PNIPAAm brush exhibited a positive gating behavior, where diffusion rates increased with increasing temperature. Nanopores modified with a thick PNIPAAm brush showed a negative gating behavior where diffusion rates decreased with increasing temperature.