Experimental and Theoretical Investigations on the Nanoscale Kinetic Friction in Ambient Environmental Conditions

Abstract

The liquid lubrication, thermolubricity and dynamic lubricity due to mechanical oscillations are investigated with an atomic force microscope in ambient environmental conditions with different relative humidity (RH) levels. Experimental results demonstrate that high humidity at low-temperature regime enhances the liquid lubricity while at high-temperature regime it hinders the effect of the thermolubricity due to the formation of liquid bridges. Friction response to the dynamic lubricity in both high- and low-temperature regimes keeps the same trends, namely the friction force decreases with increasing the amplitude of the applied vibration on the tip regardless of the RH levels. An interesting finding is that for the dynamic lubricity at high temperature, high-humidity condition leads to the friction forces higher than that at low-humidity condition while at low temperature the opposite trend is observed. An extended two-dimensional dynamic model accounting for the RH is proposed to interpret the frictional mechanism in ambient conditions.

Current trends in the physics of nanoscale friction

“…Recent FFM experiments demonstrate that high humidity at low temperature enhances the liquid lubricity while at higher temperature moisture hinders the thermolubric effect due to the formation of liquid bridges [96]. Friction response to the dynamic lubricity in both high-and low-temperature regimes keeps the same trends, namely the friction force decreases with increasing the amplitude of the applied vibration on the tip regardless of the relative humidity levels [96].…”

“…The thermally activated growth process of a capillary meniscus also affects the adhesion force between an AFM tip and a hydrophilic surface: it decreases logarithmically with the sliding velocity and vanishes at high sliding velocities [95]. Recent FFM experiments demonstrate that high humidity at low temperature enhances the liquid lubricity while at higher temperature moisture hinders the thermolubric effect due to the formation of liquid bridges [96]. Friction response to the dynamic lubricity in both high-and low-temperature regimes keeps the same trends, namely the friction force decreases with increasing the amplitude of the applied vibration on the tip regardless of the relative humidity levels [96].…”

Micro/Nanoscale Tribological and Mechanical Investigation of the Articular Surfaces of Katydid Leg Joints: Potential for the Novel Bioinspired Lubrication Systems

“…Friction traces provide information useful for assessing the processes and interactions of the two sliding surfaces [7,8]. The photographs and SEM micrographs of the surfaces studied are given in Figures 1a-c, which show that the katydids have saltatorial legs with an elongated tibia and femur adapted for jumping.…”

Vibration-induced nanoscale friction modulation on piezoelectric materials

“…Using atomic force microscopy (AFM), Socoliuc et al [12] showed that, by imposing an alternating current (AC) voltage between a conductive probe and an ionic crystal, friction could be substantially reduced owing to vibration caused by alternating electrostatic force. Similar friction modulation has also been achieved by directly vibrating the base of the AFM probe [20,21], or the sample using external transducers [22][23][24][25][26]. The effect of mechanical vibration on microscopic friction is commonly understood by the modified Prandtl-Tomlinson (P-T) model [27][28][29], where the mechanical vibration is considered as a perturbation to the interaction corrugation associated with sliding.…”

“…Furthermore, although nanoscale friction reduction has been demonstrated experimentally, the vibration driving methods so far are not easily implementable for practical applications. For instance, the alternating electrostatic force relies on the complex electrostatic interaction between the AFM probe and the sample [12,14,20], which is closely related to the dielectric constant and surface potential of the sample, and geometries of the system [30]; while the other schemes require vibration of the whole contact interface using external actuators [20][21][22][23][24][25][26], which may introduce adverse impacts on functioning of the device. Therefore, it would be highly desirable if one can tune friction by vibrating the contact interface locally in a simple way.…”