Coil-by-coil assembly of poly[acrylamide-co-3-(methacryl-amido)-phenylboronic acid] with polydiallyldimethyl-ammonium to give alizarin red S responsive films

Abstract

An electrolyte–stable polymer composite sensor film based on 2.4% boronic acid substituted polyacrylamide (poly[acrylamide-co-3-(methacrylamido)-phenylboronic acid] or P(A-MPBA)) and polydiallyl-dimethyl-ammonium chloride (or PDDACl) is obtained in a coil-by-coil deposition procedure. Based on AFM evidence, the resulting coil aggregate deposits show ca. 5–10 nm diameter and the average film thickness increases with ca. 1 nm per deposition cycle consistent approximately with the solution coil diameter. In electrochemical experiments alizarin red S is employed as a boronic acid indicating redox probe with a Langmuirian binding constant of ca. K = 4 × 10⁶ M⁻¹ and two distinct redox responses tentatively assigned here to two isomeric forms of the complex in oxidized and reduced state. Inter- and intra-coil electron transfer and electron hopping occurs during alizarin red S reduction and back-oxidation. Both smooth and mesoporous ITO substrates are employed.