We develop a general model that describes the electrical responses of thickness-shear mode resonators subject to a variety of surface conditions. The model incorporates a physically diverse set of single-component loadings, including rigid solids, viscoelastic media, and fluids (Newtonian or Maxwellian). The model allows any number of these components to be combined in any configuration. Such multiple loadings are representative of a variety of physical situations encountered in electrochemical and other liquid-phase applications, as well as gas-phase applications. In the general case, the response of the composite load is not a linear combination of the individual component responses. We discuss application of the model in a qualitative diagnostic fashion to gain insight into the nature of the interfacial structure, and in a quantitative fashion to extract appropriate physical parameters such as liquid viscosity and density and polymer shear moduli.

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Oxidative electrochemical polymerization of (N,N ′-ethylenebis(salicylideneaminato)) nickel(II), [Ni(salen)], in acetonitrile/TEAP was reinvestigated. The polymers were characterized by in situ FTIR and UV-visible spectroscopies in order to explore film structure and to clarify the electronic states as a function of the electrochemically controlled applied redox potential; oxidized species involved in polymerization and oxidative switching of the polymer were also assessed by ex situ EPR experiments. Integration of data from all techniques revealed that (a) electropolymerization of [Ni(salen)] is ultimately a ligand-based-process that takes place through a mixture of o-and p-linking of the phenyl rings and (b) poly[Ni(salen)] exhibits physical/chemical properties that cannot be attributed to an aggregation of individual complexes, behaving rather like a polyphenylene compound, with the metal ion acting as a bridge between biphenylene moieties.

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The nickel(II) complex with H 2 saltMe, a N 2 O 2 Schiff base ligand derived from salicylaldehyde, was oxidatively electropolymerized on Pt electrodes in CH 3 CN/0.1 mol dm -3 tetraethylammonium perchlorate (TEAP) to generate polymer films that exhibit reversible oxidative electrochemical behavior in a wide potential range (0.0-1.3 V), high conductivity, and stability/durability. The films of poly[Ni(saltMe)] can be made to exhibit the three regimes of charge transport behavior by manipulation of the film thickness and the experimental time scale. Films prepared by a small number of potential cycles show thin-layer/surface-type cyclic voltammetry behavior in the scan rate range used. Thicker polymers exhibit a changeover from this thinlayer regime to diffusion control at a critical scan rate that depends on film thickness. In chronoamperometry experiments a transition from semiinfinite diffusion to finite diffusion conditions was observed at longer times following the potential step.Values of D 1/2 C for the second electrochemical stage of film oxidation redox obtained from both techniques were in good agreement. A comparison of the values for oxidative and reductive electrochemical reactions suggests that ingress of counterions and solvent swelling must occur predominantly up to 0.8V in the positive going potential scan.

Both a transmission-line model and its simpler variant, a lumped-element model, can be used to predict the responses of a thickness-shear-mode quartz resonator sensor. Relative deviations in the parameters computed by the two models (shifts in resonant frequency and motional resistance) do not exceed 3% for most practical sensor configurations operating at the fundamental resonance. If the ratio of the load surface mechanical impedance to the quartz shear characteristic impedance does not exceed 0.1, the lumped-element model always predicts responses within 1% of those for the transmission-line model.

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