Potential-Dependent Interfacial Frictional Behavior between Charged Microspheres and Gold in Aqueous Solutions

Abstract

We study the interfacial frictional behavior between negatively charged hydroxyl- and carboxyl-functionalized and positively charged amino-functionalized colloidal probes and a gold electrode (GE) through electrochemical atomic force microscopy. The charged microspheres exhibit similar potential-dependent frictional behavior, with high and low frictional forces at positive and negative gold potentials, respectively. However, normal force and X-ray photoelectron spectroscopy revealed that the oppositely charged microspheres exhibit differences in the potential-controlled friction mechanism, attributed to a rearrangement of hydrated ions and water molecules due to varying gold potentials and microsphere properties. At the positive potential, surface polar groups on the negatively charged microspheres can directly form hydrogen bonds with an ice-like water layer on the gold surface, thereby increasing friction, whereas the positively charged microspheres rely on the hydrated Cl– ions adsorbed on the surface to form a hydrogen bond with the ice-like water layer. At the negative potential, the lubrication of the hydrated Na+ ions between the negatively charged microspheres and the GE reduced friction and facilitated superlubricity. However, at the interface between the positively charged microspheres and the GE, the electrostatic force generated by the hydration ions with different electrical properties increases frictional energy loss, but the lubrication of hydrated Na+ ions at the interfaces continues to induce superlubricity. The influence of different surface charges/potentials on interfacial adhesion and friction behavior is discussed in line with the mechanism of potential-controlled friction, which aids in the design of controllable friction devices in water-based environments.

A Review of Electric Potential-Controlled Boundary Lubrication

“…Experimental results from a surface force apparatus (SFG) and AFM indicate that under positive potentials in the electrolyte, a viscous ice-like water layer forms on the gold surface [76][77][78][79]. Pashazanusi and Li et al [33,34,[80][81][82] proposed that strong hydrogen bonding between this ice-like water layer and the polar friction materials accounts for the high friction. Thus, the tribological mechanism of potential modulation on gold surfaces in salt solutions warrants further investigation.…”

“…The adhesion and friction between interfaces under a positive potential are primarily attributed to the hydrogen bonding force between the ice-like water layer and the hydroxyl groups on the SiO 2 surface, as illustrated in Figure 11. Recently, Li et al [82] also identified differences in hydrogen bonding mechanisms between positive microspheres (−NH 3 terminal microspheres) and negative microspheres (−OH and −COOH terminal microspheres) and the ice-like water layer. Negative microspheres directly form hydrogen bonds with the ice-like water layer through surface polar groups, while positive microspheres generate hydrogen bond sets with the ice-like water layer through hydrating anions adsorbed on the surface within their hydration shell.…”

Electric-field frictional effects in confined zwitterionic molecules

“…[1][2][3][4] In particular, the tuning role of applied electric fields in confined geometries has been widely investigated in triboelectrochemistry experiments. [5][6][7][8][9][10][11][12][13] In most of these experiments ions move in a liquid solution driven by the applied field, covering and effectively modifying the sliding surfaces, thus inducing changes in friction. [14][15][16][17][18][19][20][21][22] An alternative approach is based on the ability of the electric field to reorient macromolecules, thus changing their conformation in aqueous solution [23][24][25] and dry environments, [26][27][28] with potentially dramatic effects on friction.…”