Electrochemical Characterization of Nanoporous Films Fabricated from a Polystyrene-Poly(methylmethacrylate)Diblock Copolymer:Monitoring the Removal of the PMMA Domains and Exploring the Functional Groups on the Nanopore Surface

摘要

Cyclic voltammetry(CV)was used to assess fabrication of a nanoporous film from a polystyrene-poly(methyl methacrylate)diblock copolymer(PS-b-PMMA)and also to explore the surface functional groups on the resulting nanopores.Polymer films containing vertically aligned cylindrical nanoscale pores(ca.10 nm in pore radius,20-30 nm in film thickness)were prepared on gold substrates by removing the cylindrical PMMA domains from PS-b-PMMA films via UV irradiation and subsequent acetic acid treatment.CV measurements provided a simple means for monitoring the extent of the removal of the PMMA domains and for assessing the formation of a recessed nanodisk-array electrode(RNE)structure.The resulting RNEs exhibited a decrease in redox current of anionic Fe(CN)_6~(3-)with increasing solution pH from 4.6 to 6.3 and a negligible change in CV of uncharged l,l'-ferrocenedimethanol.The decrease in redox current of Fe(CN)_6~(3-)at the higher pH was due to electrostatic repulsion between Fe(CN)_6~(3-)and the electrical double layer formed in the neighborhood of the negatively charged nanopore surface.Indeed,the reduction of effective.pore radius measured from CVs of Fe(CN)_6~(3-)was correlated to the change in the thickness of the electrical double layer.The pH range that showed the decrease in redox current of Fe(CN)_6~(3-)was consistent with the presence of -COOH groups on the nanopore surface,although they were not detected using Fourier transform infrared spectra of etched PS-b-PMMA films.