Influence of Humidity on Friction Forces in Point-Contact under Small Loads

Abstract

The frictional force in point-contact between a Si 3 N 4 probe and a polished SUS304 steel surface was investigated by lateral force microscope under different press forces and relative humidity (RH). Variations in the coef cient of friction due to adsorbed water and meniscus necking between the probe and the steel surface were analyzed. At 65% RH, the coef cient of friction between the probe and the hydrophilic surface sharply decreased from 4.0 to 1.0 as vertical nominal load increased from 6 nN to 35 nN, slowly decreasing to 0.7 when the load was increased to 66 nN. At a vertical load of 14 nN, the coef cient of friction for a hydrophilic surface increased with humidity, peaking at 3.5 at an RH of 65%, but decreasing when RH increased to 80%. The change was analyzed to be due to the amount of adhered water on the surface and the formation of meniscus necking. The coef cient of friction on a hydrophobic surface with 1H,1H,2H,2H-per uorodecyltriethoxysilane (PFDS) was much lower and independent of humidity, despite the much large adhesion force occurred between probe and PFDS molecular.

Electro-Wetting Behavior of Sodium Chloride Aqueous Solution on Hydrophobic Surfaces of Stainless Steel and Its Influence on Polarization

“…This nding was similar to the results observed on at 316-PE and 316-PFDS surfaces 12,13) . The deposited PFDS is likely a monomolecular layer of 2 nm thickness 12,20) , with the deposited PE also being several nanometers thick. Figure 4 shows an example of the CAs of aqueous solution of 3.5% NaCl before and after application of positive currents of 0.5, 0.75 and 1.0 mA to the 304-PE and 304-PFDS plane surfaces.…”