“In-situ” Quartz Crystal Microbalance Responses and Electrochemistry Regarding Langmuir–Blodgett Film of Viologen Polyion Complex on the Electrode Surface

Abstract

Abstract The electrochemical behavior and the response of the quartz crystal microbalance(QCM) for the Langmuir–Blodgett(LB) viologen film have been examined. LB monolayers employed are prepared by electrostatically fixing the viologen monolayer containing the alkyl chain moiety on the poly(potassium 1-sulfatoethylene). The number of monolayers accumulated on the polycrystalline Au electrode of a piezoelectric quartz crystal was controlled by changing the general vertical dipping times. The QCM frequency response for the first reduction scan of viologen dication (V2+) to monocation radical (V+•) shows extremely large frequency increase, qualitatively indicative of mass loss, viscoelasticity decrease, or mechanical stress decrease during the reduction. A frequency increase during the second reduction scan is also observed, although not as large as for the first scan. The frequencies increase continuously with increasing number of scans and the steady-state responses can only be obtained after many repetitive potential scans. The results of the conductance spectra measurements of the quartz crystal/LB film composite resonator are interpreted as break-in and/or an increase of aggregation of the orientated structure during potential scans. The cyclic voltammetric wave obtained in the potential range 0 to −0.7 V vs. sodium chloride saturated calomel electrode has the characteristics of a simple, one electron transfer between V2+ and V+•, being chemically reversible process. The subsequent cyclic voltammogram responses obtained after the first cycle of potential scan are nearly identical for some hours, in contrast to the responses of the QCM. It is shown that structural change of the organized film dose not have a significant influence on the shape of the electrochemical response but does have an effect on the frequency response of the QCM.