Conductance and Flux Measurements on Capillary-Incorporated Nanoporous Monoliths Derived from a Polystyrene-Poly(Methylmethacrylate) Block Copolymer

This paper reports ionic conductance and molecular flux measurements for characterizing microcapillary-incorporated nanoporous monoliths derived from a cylinder-forming polystyrene-poly(methylmethacrylate) diblock copolymer. Such monoliths were fabricated by introducing molten polymer into the end of quartz microcapillaries, followed by UV irradiation and acetic acid treatment. The ionic conductance across the monoliths in 1:1 electrolyte solution decreased with decreasing electrolyte concentration from 0.10 M to 1.0 mM, reflecting bulk ionic conductance. In contrast, it became constant at concentrations ≤ 0.10 mM, governed by surface conductance determined by the cation surface mobility and the surface charge density of the negatively-charged nanopores. Although the conductance data and scanning electron microscopy images indicated the presence of monolith cracks with sizes significantly larger than the expected nanopore size (10 nm in radius), observation of the permselective exclusion of anionic sulforhodamine B from the negatively charged nanopores indicated that the solvated species were mainly transported through nanoscale pathways.