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The transmission-line model has been theoretically developed for a TSM resonator sensor, leading to a lumped-element model. Both models have been used to compute expected responses for typical sensing applications. Particular attention is paid to the shift in the series resonance frequency and the rise in resonance damping because of surface loading. A quantitative means to determine the utility of the lumped-element model is established from the relative deviations in the two parameters.

Effective removal of fingerprint deposits is crucial for experimentation related to the corrosion of metals by fingerprint deposits. Such removal is also necessary prior to deposition of test fingerprints. The effectiveness of four regimes in removing fingerprint deposits from brass is considered. Sustained wiping of the deposit with a tissue at applied pressures of up to c. 1430 Pa or rubbing while the brass was immersed in acetone both failed to remove completely all traces of fingerprint deposits. Heating the brass to 600°C was an effective remover; however, this also oxidized the surface of the metal except where inhibited by fingerprint deposits. The most effective regime, and the only one of the four that removed all traces of deposit without affecting the properties of the metal surface, was immersion in warm soapy water while rubbing with a tissue. We propose this as the preferred method for fingerprint removal. [ABSTRACT FROM AUTHOR]

Vesicle fusion was used to deposit mixed dimyristoyl phosphatidylethanolamine–dimyristoyl phosphatidylserine (DMPE–DMPS) phospholipid bilayers on Au electrodes. Bilayer structure and composition, when exposed to aqueous NaF and subject to an applied electrochemical potential, were studied using electrochemical, spectroscopic and neutron reflectivity (NR) techniques. Interfacial capacitance data indicate the formation of compact films. Chronocolometric data show that surface charge is significantly altered by the presence of lipid in the potential range −0.75 < E/V (AgAgCl) < 0.35. NR measurements were made on lipid films in which the hydrocarbon tails were either fully hydrogenous (h-DMPE–h-DMPS) or perdeuterated (d-DMPE–d-DMPS), in each case serially exposed to D2O and H2O electrolytes and subject to different applied potentials. Guided by simulations of candidate interfacial structures, these yield the spatial distributions of lipid and solvent within the layers. Adjacent to the electrode, a compact inner leaflet is formed, with potential-dependent solvent volume fraction in the range 0.09 < S< 0.19; there was no evidence of an intervening water layer. The outer leaflet contains rather more solvent, 0.52 < S< 0.55. NR-derived film thickness and PM-IRRAS intensity data show that the lipid molecules are tilted from the surface normal by ca.26°. Bilayer solvation and charge data show a strong correlation for the inner leaflet and very little for the outer leaflet. [ABSTRACT FROM AUTHOR]

Time-resolved specular neutron reflectivity measurements are presented and interpreted for electroactive polyvinylferrocene (PVF) films subject to potentiodynamic electrochemical control. New data acquisition methodology allows an effective measurement time scale on the order of seconds, which is an improvement over conventional methodology by 2 to 3 orders of magnitude. Reflectivity profiles were obtained for PVF films exposed to aqueous 0.1 M NaClO4in which PVF films are thermodynamically permselective, with contrast variation via H2O and D2O. Irrespective of any model, the raw profiles show chemically reversible film “breathing” due to redox-driven solvent entry and exit during polymer oxidation and reduction, respectively. Modeling reveals three compositionally distinct regions within the polymer film: interfacial regions at the electrode and solution interfaces and a “bulk” interior. The new methodology, supported by simultaneous in situ visible transmission spectroscopy, reveals an unprecedented level of insight into the temporal and spatial mechanistic details of film solvation changes, including a two-stage (de)solvation mechanism for redox switching, differences in interior (in)homogeneity for reduced and oxidized films, and permselectivity failure under dynamic electrochemical conditions for the reduced (but not oxidized) state, in contrast to static conditions that allow permselectivity for both states. [ABSTRACT FROM AUTHOR]

Electrochemical, acoustic wave and imaging (AFM) methods were used to characterize electroactive poly[Ni(3-Mesalophen-b15-c5)] films. The distinct physical principles of these techniques generate different responses to film characteristics, such that their simplistic correlation in the context of a single uniform film model does not adequately describe the data. Film behaviour can only be rationalised using a two layer model comprising a dense (poorly solvated) inner layer and an outer layer comprising islands of diffuse (highly solvated) polymer. The two layers can be observed directly by AFM imaging. The balance of their contributions shifts with polymer coverage: the inner layer dominates thin films and the outer layer dominates thick films. The inner layer is acoustically more rigid and, even if ion transport is slow, is sufficiently thin as to pose no major barrier to electrochemical communication with the underlying electrode. For very thin films, gravimetric interpretation of the acoustic wave response correlates simply with coulometric data; thicker films require viscoelastic phenomena to be considered. The low polymer segment density of the outer layer facilitates ion transport but results in weak acoustic coupling, such that the acoustic and coulometric assays differ. By combining the AFM, acoustic wave and electrochemical responses one can establish a quantitative picture of component layer populations and characteristics. [ABSTRACT FROM AUTHOR]

EQCM experiments were carried out on PEDOT films exposed to TEABF4/CH3CN and TEABF4/CH2Cl2 under permselective conditions and subjected to cyclic voltammetry in the potential range corresponding to p-doping. Current and frequency responses were used to obtain time-resolved ion and solvent flux data as functions of potential. Normalization of these fluxes with potential scan rate distinguishes thermodynamically (ir)reversible elementary steps in the overall redox process. The specific mechanisms are different in the two solvents, although both show mechanistic switches at partial redox conversion during both p-doping and undoping. These different mechanistic signatures are characterized according to the solvent identity, by different patterns of deviation from scan rate normalization for the experimentally measured ion and solvent fluxes. Comparison of these ion and solvent fluxes demonstrates that the rates of solvent expulsion (during doping) and entry (during undoping) are key determinants of mechanism. In both switching directions there are changes between kinetically limiting and rapid solvent transfer that depend upon solvent identity, i.e. the mechanism depends substantially upon charge state, switching direction and solvent. These mechanistic pathways and shifts can be visualized by a scheme-of-cubes representation. [ABSTRACT FROM AUTHOR]

Polyaniline itself can be converted to its conductive form from its insulating form by applying an oxidising potential in which polyaniline is converted to its positive charge state. Anions in the target solution are driven into the positively charged polymer film by electrostatic force, and this process is reversed when a reduction potential is applied. Consequently, interfacial processes of polyaniline modified electrode make it viable to remove undesirable ions from the target solution. During this process, polyaniline operates as an ion-exchanger by directing specific ions at definite potentials, which is the principle of the electrochemically switched ion-exchange technique. Therefore, polyaniline can be employed as a convenient material to perform as a new ion-exchanger modified film in an acidic environment. On the other hand, an abrupt decrease in the electroactivity of polyaniline at elevated pH values restricts its use in such practical applications. To overcome this problem, copolymerization of aniline and o -toluidine is expedient as it will be able to enhance the electrochemical properties of polyaniline. Hence, several copolymers were synthesised in the presence of different aniline and o -toluidine feedstock ratios. It was found that the surface coverage value of a representative poly(aniline- co - o -toluidine) copolymer film was 139.7 nmol cm−2 compared with 76 nmol cm−2 for pure Pani under identical conditions. In addition, the redox cycling in monomer-free NaF solutions showed that the poly(aniline- co - o -toluidine) film exhibited excellent reversibility between redox reactions at pH 6.60. These outcomes clearly illustrate the contribution of o -toluidine to the electrochemical properties of polyaniline at raised pH medium. [ABSTRACT FROM AUTHOR]

The electrochemical quartz crystal microbalance was used to determine redox-driven ion transfers accompanying p-doping of polypyrrole (PPy) films in the choline chloride-based deep eutectic ionic liquid ethaline; electroneutrality maintenance is gravimetrically dominated by choline cation transfer and this requires the presence within the undoped film of ionic liquid, when this finite reservoir of choline is exhausted there is a shift to chloride transfer. [ABSTRACT FROM AUTHOR]

EQCM experiments were carried out on PEDOT films exposed to TEABF(4)/CH(3)CN and TEABF(4)/CH(2)Cl(2) under permselective conditions and subjected to cyclic voltammetry in the potential range corresponding to p-doping. Current and frequency responses were used to obtain time-resolved ion and solvent flux data as functions of potential. Normalization of these fluxes with potential scan rate distinguishes thermodynamically (ir)reversible elementary steps in the overall redox process. The specific mechanisms are different in the two solvents, although both show mechanistic switches at partial redox conversion during both p-doping and undoping. These different mechanistic signatures are characterized according to the solvent identity, by different patterns of deviation from scan rate normalization for the experimentally measured ion and solvent fluxes. Comparison of these ion and solvent fluxes demonstrates that the rates of solvent expulsion (during doping) and entry (during undoping) are key determinants of mechanism. In both switching directions there are changes between kinetically limiting and rapid solvent transfer that depend upon solvent identity, i.e. the mechanism depends substantially upon charge state, switching direction and solvent. These mechanistic pathways and shifts can be visualized by a scheme-of-cubes representation.