Piezoelectric resonator and drag force study of the properties of an interfacial hexafluorophosphate solution layer at gold electrode surface

Abstract Piezoelectric resonator measurements show that there is a minimum of interfacial viscosity of sodium hexafluorophosphate aqueous solution (approximately 1% of the bulk viscosity) at the potential of zero charge of gold electrode. Drag force measurements confirm interfacial viscosity dependence on the potential obtained from piezoelectric resonator measurements but the minimum is lower (approximately 5% of the bulk viscosity). Potential dependence of interfacial viscosity has been determined in the absence of confinement of fluid between a probe and surface what provides useful comparison to probe-based methods where confinement is inherent to the measurement and where additional model assumptions are needed to separate confinement effects. By controlling the applied potential it is possible to control the viscosity of liquid layer close to the solid interface, what increases the ability to actively manipulate a wall-bounded liquid flow field to effect a desired change.