Mesoporous hybrid thin film membranes with PMETAC@Silica architectures: Controlling ionic gating through the tuning of polyelectrolyte density

Manipulating molecular transport through mesoporous hybrid films is a fascinating approach toward mimicking transport in nature. To understand the details in controlled transport, it is necessary to gradually adjust the charge density that in turn results in a precise adjustment of permselectivity. We have created hybrid architectures through the controlled polymerization of a strong polyelectrolyte: (2-methacryloyloxy)ethyltrimethylammounium (PMETAC) in a mesoporous thin silica film. PMETAC contents from 5 to 100% filling can be obtained by choosing a temperature or light-induced polymerization route and by varying polymerization times, as proven by ellipsoporosimetry and infrared spectroscopy. Using cyclic voltammetry, we demonstrate that a gradual variation of ionic permselectivity from a silanol-regulated to a PMETAC-regulated permselectivity can be obtained by tuning the PMETAC mesopore filling. The resulting behavior ranges from ion exclusion to preconcentration. The experimental observations are correlated with theoretical calculations that provide quantitative insights into the organization of the ions and polymers within the pore. Our findings shed light into the understanding of the interplay between charge density and space on molecular transport, leading toward the rational design of selectively transporting synthetic membranes.