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| - Nanometer-Scale Probing of Potential-DependentElectrostatic Forces, Adhesion, and Interfacial Friction atthe Electrode/Electrolyte Interface
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| - The atomic force microscope (AFM) was used to examine the influence of an applied electrochemicalpotential on the interfacial properties of the electrode/electrolyte interface. Measurements of electrostaticforce, adhesion, and friction coefficient were performed at two different electrode surfaces: glassy carbonand a thin film of sulfonate-derivatized poly(aniline) (SPANi). At the carbon electrode, changes in electrostaticforce between probe and substrate exhibited a potential-dependent transition from repulsive to attractivevalues at potentials negative and positive of the potential of zero charge (Epzc). Simultaneous measurementsof tip−substrate adhesion and friction coefficient showed a change from low to high values over the samepotential range, suggesting a common mechanism dominated by the electrostatic force. Measurement ofthese same properties at a SPANi-coated electrode also displayed a potential-dependent response. Theelectrostatic force and the adhesion tracked with the oxidation state of the initially neutral film. However,the friction coefficient appeared insensitive to the charge state of the polymer. A calculation of the forcesbetween probe and substrate using DLVO theory accurately reflected the measured force curves as wellas the change in adhesive force as a function of surface charge. Consideration of the forces that determinethe friction coefficient suggested that the influence of electrostatic interactions was strongly dependentupon the geometry of the tip−sample contact and the presence of microgaps between the tip and thesubstrate over which electrostatic forces could operate. The absence of potential-dependent friction at theSPANi/electrolyte interface reflected a compliant substrate, which gave rise to a predominantly adhesivetip/sample contact.
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