title: Effect of the charge and roughness of surfaces on normal and friction forces measured in aqueous solutions.
abstract: We used the atomic force microscope (AFM) to determine how the roughness and charge on a surface affect the adhesion and friction when measured against a smooth surface (colloid probe) in an aqueous solution. The effect of roughness was investigated by coating TiO2 crystal substrates with TiO2 nano- or micro-sized particles, where an increase in the particle size increased the RMS roughness of the substrate. The charge of the substrate was varied by changing the pH of the aqueous solution. Force-separation curves and friction-load data were measured for the smooth colloid probe-rough substrate systems. The adhesion and friction between two surfaces in solution were seen to depend on the surface charge and roughness. A noncharged surface gave the greatest adhesion, while a charged surface gave weaker adhesions. Increasing the roughness of the surface resulted in a stronger adhesion. The magnitude and range of the adhesions were not affected by the measuring velocity in the case of a noncharged substrate but decreased with an increasing velocity for charged surfaces. The friction was seen not to depend on roughness in the case of a noncharged surface. However, in the case of a charged surface, the friction decreased with an increased roughness for low loads and then showed no dependence on the surface roughness for high loads. The results of this experiment show that the adhesion and friction of a system can be decreased via the roughness and charge of the substrate and the ion types in the solution.
authors.affiliation: Shinshu University, Ueda, Nagano, Japan. mcnamee@shinshu-u.ac.jp
authors.forename: Cathy E
authors.initials: CE
authors.lastname: McNamee
authors.forename: Ko
authors.initials: K
authors.lastname: Higashitani
mesh_terms: D017276:Friction; D018625:Microscopy, Atomic Force; D053758:Nanoparticles / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: C009495:titanium dioxide; D014025:Titanium