Temperature dependence of solvation forces as measuredin atomic force microscopy

摘要

An atomic force microscope (AFM) has been used to study the effect of temperature on solvationforces in the liquids octamethylcyclotetrasiloxane, n-hexadecane, and n-dodecanol confinedbetween the AFM tip and a graphite surface. Discrete solvation layers can be observed for all threeliquids at all the temperatures measured (298-348K). However, with increasing temperature there isa significant decrease in the magnitude of the measured solvation forces and a reduction in thenumber of solvation oscillations which can be observed. Solvation forces per se are only weaklytemperature dependent and the most plausible explanation is that we are measuring how the layersare squeezed from the tip-sample gap. The squeeze out process is a thermally activated phenomenonand gives rise to the large change in the magnitude of the force oscillations with temperature. Asimple analysis is provided based on transition rate theory. The large change in solvation force withtemperature has implications for the measurement of localized forces using AFM, particularly ininterpreting biological interactions and single asperity friction.