Direct measurement of plowing friction and wear of a polymer thin film using the atomic force microscope

Nanometer-scale plowing friction and wear of a polycarbonate thin film were directly measured using an atomic force microscope (AFM) with nanoscratching capabilities. During the nanoscratch tests, lateral forces caused discrepancies between the maximum forces for the initial loadings prior to the scratch and the unloading after the scratch. In the case of a nanoscratch test performed parallel to the cantilever probe axis, the plowing friction added another component to the moment acting at the cantilevered end compared to the case of nanoindentation, resulting in an increased deflection of the cantilever. Using free-body diagrams for the cases of nanoindentation and nanoscratch testing, the AFM force curves were analyzed to determine the plowing friction during nanoscratch testing. From the results of this analysis, the plowing friction was found to be proportional to the applied contact force, and the coefficient of plowing friction was measured to be 0.56 +/- 0.02. Also, by the combination of nanoscratch and nanoindentation testing, the energetic wear rate of the polycarbonate thin film was measured to be 0.94 +/- 0.05 mm(3)/(N m).

Experimental measurement of polyethylene chain modulus by scanning force microscopy

Nanoindentation technique and scanning force microscopy have been used to measure directly the polyethylene modulus along the chain axis. Single crystals of polyethylene were employed in order to obtain well-aligned chain segments. To minimize effects of scanner creep, a Z scan rate of 3 Hz was employed. The "X Rotate" value of 25 degrees was selected to eliminate effects of lateral tip motion. The results were analyzed by the Oliver -Pharr method for which direct observation and measurement of the contact area are not required. Considering the influence of tip roundness on the projected contact area, the nanoindentation results were analyzed by the Sawa method. The chain modulus obtained from the thinner polyethylene single crystal sample was 204 +/- 21 GPa by the Oliver-Pharr method and 168 +/- 17 GPa by the Sawa method. The lower values than expected were due to substrate effects and anisotropy of chain deformation during nanoindentation. An extrapolation of the chain modulus obtained by various strains to zero nanoindentation eliminated the effect of substrate and anisotropy of chain deformation. The corresponding chain modulus obtained from the thicker sample was 278 GPa by the Oliver-Pharr method and 267 GPa by the Sawa method, respectively, in better agreement with the value of 340 Cpa determined theoretically. (C) 2001 Elsevier Science Ltd. All rights reserved.

Atomic force microscopy imaging of molybdenum oxide film electrodeposited on a carbon electrode

Non-stoichiometric mixed-valent molybdenum(VI, V) oxide film was grown on carbon substrates by the electrodeposition method. Responses of the prepared molybdenum oxide thin films to potential and to different solution acidities were studied by cyclic voltammetry, and the corresponding morphological changes of the film were monitored by atomic force microscopy (AFM). AFM images of the molybdenum oxide film show that the characteristic domed structure on the film surface increased during the transition from the oxidized state to the reduced state without signification change in the KMS surface roughness value. Furthermore, AFM studies show that the solution acidity has great effect on the morphology of the films, and the films undergo a homogenizing process with increasing pH of the solutions. (C) 1999 Elsevier Science S.A. All rights reserved.

The kinetics study in liquid-liquid systems with constant interfacial area cell with Laminar flow

A novel constant interfacial cell with laminar flow is proposed as an approach to obtain extraction kinetics data in liquid-liquid systems. Applications and theoretical fundamentals of the apparatus have been elaborated.. The equation which can express the mass transfer of liquid-liquid system run in the constant interfacial cell with laminar flow is deduced. Simulations from the equations indicate that diffusivity is a suitable factor to represent the characteristics of extraction kinetics rather than the extraction rate in the diffusion controlling step. The dependence of the aqueous phase concentration on time is recommended to determine the extraction regime. The diffusivities of the EuCl3-HDEHP extraction system obtained by different methods are compared to certify the hydrodynamic theory of the cell. The diffusivities of the ErCl3-HEH/EHP extraction system are determined, which show that this technique is a convenient method to obtain the diffusivities in the liquid-liquid system and to determine the extraction regime. (C) 1998 Elsevier Science Ltd. All rights reserved.

Effect of Eu3+ on the domain structures in phosphatidylcholine LB monolayer film observed by atomic force microscopy

Ordered domain structures were observed by atomic force microscope in dipalmitoylphosphatidycholine monolayer film, which was spread on the subphase of Eu3+ solution.

Electrochemical scanning tunneling microscopy and electrochemical quartz crystal microbalance study of the adsorption of phenanthraquinone accompanied by an electrochemical redox reaction on the Au electrode

In situ electrochemical scanning tunneling microscopy (ECSTM) and an electrochemical quartz crystal microbalance (EQCM) have been employed to follow the adsorption/desorption processes of phenanthraquinone (PQ sat. in 0.1 mol l(-1) HClO4, solution) accompanied with an electrochemical redox reaction on the Au electrode. The result shows that: (1) the reduced form PQH(2) adsorbed at the Au electrode and the desorption occurred when PQH(2) was oxidized to PQ; (2) the adsorption process initiates at steps or kinks which provide high active sites on the electrode surface for adsorption, and as the potential shifts to negative, a multilayer of PQH(2) may be formed at the Au electrode; (3) the reduced PQH(2) adsorbed preferentially in the area where the tip had been scanned continually; this result suggests that the tip induction may accelerate the adsorption of PQH(2) on the Au(111) electrode. Two kinds of possible reason have been discussed; (4) high resolution STM images show the strong substrate lattice information and the weak monolayer adsorbate lattice information simultaneously. The PQH(2) molecules pack into a not perfectly ordered condensed physisorbed layer at potentials of 0.1 and 0.2 V with an average lattice constant a = 11.5 +/- 0.4 Angstrom, b = 11.5 +/- 0.4 Angstrom, and gamma = 120 +/- 2 degrees; the molecular lattice is rotated with respect to the substrate lattice by about 23 +/- 2 degrees. (C) 1997 Elsevier Science S.A.

Determination of the standard heterogeneous rate constant in polyelectrolyte using steady state microdisk voltammograms

The steady state voltammogram at a microdisk electrode is used to measure the diffusion coefficient and standard heterogeneous rate constant (k(s)) of ferrocene in polyelectrolyte PEG + LiClO4. The k(s) obtained is smaller in polyelectrolyte than in liquid medium. It is proposed that the polymer solvent electron transfer dynamics are affected by the relaxation rates of the ether dipole sites on the polymer chains, which are in turn constrained by the rates of polymer chain segment, or local structure, relaxations. The dependence of k(s) on temperature is observed. The k(s) increases with increasing temperature.

Lanthanide ion induced formation of stripes domain structure in phospholipid Langmuir-Blodgett monolayer film observed by atomic force microscopy

Long-range ordered stripes domain structures were observed in Dipalmitoylphosphatidylcholine (DPPC) Langmuir-Blodgett monolayer film which was spread on the subphase of lanthanide ion (Eu3+) solution and transferred to a freshly cleaved mica substrate by vertical deposition. This novel phenomenon was discussed in terms of the competitive interaction of dipole-dipole and electrostatic interactions of the DPPC molecules combined with lanthanide ions with those DPPC molecules free of lanthanide ions.

STUDY ON ELECTROCATALYTIC OXIDATION OF NADH BY FERROCENE DERIVATIVES AND DETERMINATION OF CATALYTIC RATE-CONSTANT AT MICRODISK ELECTRODE

The electrocatalytic oxidation of NADH by ferrocene derivatives and the influence of complexation with beta-cyclodextrin (beta-CD) were investigated at a microdisk electrode in a buffer solution. The cyclic voltammetric behavior of the ferrocene derivatives on the microdisk electrode was used to determine the electron-transfer rate constant from NADH to the ferricinium species. The heterogeneous rate constants and the diffusion coefficient of ferrocene derivatives were determined with the microdisk electrode. The effect of temperature and pH on the electrocatalytic oxidation of NADH were assessed.

SCANNING-TUNNELING-MICROSCOPY (STM) AND LATERAL FORCE MICROSCOPY (LFM) INVESTIGATION OF THE STRUCTURE AND CHARACTER OF CONDUCTIVE POLYPYRROLE FILM

Polypyrrole doped with p-toluenesulfonate was electropolymerized onto highly oriented pyrolytic graphite (HOPG), glassy carbon (GC) and Pt electrode surfaces under the same experimental conditions. The resulting films were studied by scanning tunneling m

APPLICATIONS OF RAPID SCAN SPECTROELECTROCHEMISTRY - DETERMINATION OF HETEROGENEOUS ELECTRON-TRANSFER RATE-CONSTANT OF BILIVERDIN OXIDATION

The rapid scan spectrometer was used to determine the heterogeneous electron transfer rate parameters for the oxidation of Biliverdin in DMF by single potential step thin layer spectroelectrochemical techniques and yielded an average formal heterogeneous electron transfer rate constant K(s, h)0' = 2.45 (+/-0.12) x 10(-4) cm s-1, electrochemical transfer coefficient alpha = 0.694+/-0.008. The oxidation process of Biliverdin was also studied and the formal potential E0 = 0.637 V (vs. Ag/AgCl) was obtained.

DETERMINATION OF THE RATE-CONSTANT OF A CATALYTIC REACTION USING A PARALLEL INCIDENT SPECTROELECTROCHEMICAL CELL

The possibility of determining the rate constant of a catalytic reaction using a parallel incident spectroelectrochemical cell was investigated in this work. Various spectroelectrochemical techniques were examined, including single-potential-step chronoabsorptometry, single-potential-step open-circuit relaxation chronoabsorptometry and double-potential-step chronoabsorptometry. The values determined for the kinetics of the ferrocyanide-ascorbic acid system are in agreement with the reported values. The parallel incident method is much more sensitive than the normal transmission method and can be applied to systems which have smaller molar absorptivities, larger rate constants or lower concentrations.