Poly(2-(dimethylamino)ethyl methacrylate)-Modified Nanoporous Colloidal Films with pH and Ion Response

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes were grown using surface-initiated atom transfer radical polymerization on the nanopore surface inside the colloidal films assembled from 255 nm silica spheres. The molecular transport through PDMAEMA-modified colloidal nanopores was studied as a function of pH and ionic strength by measuring the flux of neutral and positively charged redox-active species across the colloidal films using cyclic voltammetry. Nanopores modified with PDMAEMA brushes exhibited pH- and ion-dependent behavior as follows. The diffusion rates decreased with decreasing pH as a result of electrostatic interactions and steric hindrance. At low pH (in the protonated state) the diffusion rates increased with increasing salt concentration because of the charge screening. We also quaternized the surface-grafted PDMAEMA, which led to the formation of strong polyelectrolyte brushes that hindered the diffusion of neutral molecules through the nanopores due to steric effects and the diffusion of positively charged species due to both electrostatic and steric effects.