Polyaniline film, EQCM

Fig. II. 10.7 (a) Cyclic voltammograms (two cycles) and (b) the simultaneously detected EQCM frequency changes for a polyaniline film (L = 2.9 jJLm) in contact with 1 M H2SO4. Sweep rate lOOmVs ...

In the case of the redox of polyaniline films, charge compensation is basically achieved by anion transport. However, the actual ion transport is influenced by the solution pH. Grata and Buttry [63] first examined this process using EQCM. Two redox waves appeared in the cycKc voltammograms in aqueous solutions. The first redox wave is attributed to the redox between the fully reduced polyaniline form and emeraldine salt. In the case that... 

Calvo and Etchenique summarized in their review some further in situ combinations of EQCM with non-electrochemical techniques (see [35] and references therein). For example, EQCM was also combined with ellipsometry in order to study the nucleation and growth of polyaniline films (reference 24 in [35]) or the viscoelastic behavior of poly(7-methyl-L-co y-n-octadecyl-L-glutamate) [17]. EQCM was combined with UV-visible absorption spectroscopy, in order to investigate the redox reactions of viologens. A combination of EQCM and probe beam deflection, PBD, was also reported in the literature (references 29, and 30 in [35], and [81]). PBD can discriminate between anion, cation, and solvent fluxes that might be generated on the electrode surface. 

Bacskai et al. [86] used EQCM responses to study the influence of electrolyte composition and pH on polyaniline film. These authors have observed the ingress of solvent over the entire potential range. The film become increasingly porous as its distance increased from the electrode surface, i.e. film which is directly in contact with metal is more compact. 

By combination of ellipsometry and EQCM Gottesfel [24] studied the nucleation and growth of polyaniline (PANI). The mass deposited was obtained by the frequency change while the thickness resulted from the ellipsometry measurements. Therefore the variations of mass and PANI film density were followed in real time, which would otherwise be impossible with either individual technique alone. 

One of the other attractions of polyaniline is the ease of preparing (or even commercial availability) of substituted derivatives. The simplest example is the methyl derivative poly(o-toluidine), for which the EQCM in conjunction with PBD has been used to obtain the individual anion, cation, and solvent fluxes/film populations. By comparing the EQCM frequency responses to a potential sweep [46] and a potential step [154], it is possible to show that the competing ion transfers have intrinsic potential and timescale dependencies the contributions of the protons and perchlorate ions are also pH dependent. One interesting feature is that anion... 

Fig. 24 Variation of EQCM resonant frequency with simultaneously ellipsometrically determined film thickness during deposition of polyaniline. Electrode Ron 5-M Hz AT-cut quartz crystal. Solution ...

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