Interfacial frictional behavior

Attractive or repulsive interaction between two solid surfaces should play an important role in the interfacial frictional behavior [87,92-95]. From previous theoretical [89] and experimental investigations [87, 95], it was known that the attractive interaction result in a high friction and repulsive interaction results in low friction force. To characterize the interfacial molecular structure between two solids under electrostatic interaction is also important to elucidate the frictional properties of two solids. 

Dutrowski [5] in 1969, and Johnson and coworkers [6] in 1971, independently, observed that relatively small particles, when in contact with each other or with a flat surface, deform, and these deformations are larger than those predicted by the Hertz theory. Johnson and coworkers [6] recognized that the excess deformation was due to the interfacial attractive forces, and modified the original Hertz theory to account for these interfacial forces. This led to the development of a new theory of contact mechanics, widely referred to as the JKR theory. Over the past two decades or so, the contact mechanics principles and the JKR theory have been employed extensively to study the adhesion and friction behavior of a variety of materials. 

Dissipation phenomena generally occur during measurement of the adherence of polymer materials, leading to an adherence energy function of both the number and nature of interfacial interactions (adhesion) and dissipative properties, mainly due to viscoelastic behavior [1-5]. Friction properties of polymers are also governed by interfacial interactions and dissipation mechanisms. Common phenomena (interfacial interaction and dissipation) therefore control adherence and friction behaviors. However, the relationship between the two phenomena is still vague or undefined. The first objective of this experimental work is then to compare adherence and friction of polydimethylsiloxane (PDMS) networks in order to establish relationships between these two properties. 

Hard BN films obtained by an ion beam extracted from a borazine plasma were investigated in order to examine their adhesion and friction behavior. It was shown that sputter-cleaned film surfaces exhibit strong interfacial adhesion and high friction. The presence of adsorbates on the BN surfaces reduces their shear strength [116 to 118]. 

In order to elucidate the general tribological features of a solvated polymer matrix, frictions of various kinds of hydrogels have been investigated in the last several years, and very rich and complex frictional behaviors have been observed [14-30]. To describe the frictional behavior of a gel sliding on a smooth substrate, we have proposed a thermodynamic model from the viewpoint of a polymer-sohd interfacial interaction [15]. 

Based on the above complex frictional behavior of polymer gels, Gong and cowoik-ers have proposed a repulsion-adsorption model from the viewpoint of polymer-solid interfacial interactions to describe the friction behavior of gels on a smooth... 

Wear. Ceramics generally exhibit excellent wear properties. Wear is deterrnined by a ceramic s friction and adhesion behavior, and occurs by two mechanisms adhesive wear and abrasive wear (43). Adhesive wear occurs when interfacial adhesion produces a localized Kj when the body on one side of the interface is moved relative to the other. If the strength of either of the materials is lower than the interfacial shear strength, fracture occurs. Lubricants (see Lubricants and lubrication) minimize adhesion between adj acent surfaces by providing an interlayer that shears easily. Abrasive wear occurs when one material is softer than the other. Particles originating in the harder material are introduced into the interface between the two materials and plow into and remove material from the softer material (52). Hard particles from extrinsic sources can also cause abrasive wear, and wear may occur in both of the materials depending on the hardness of the particle. 

Mathematical structure-property relations have yet to be developed that tie molecular level information to a prediction of friction and wear behavior. Current theories focus on idealized structures and interfacial interactions that are rarely realized in practice. Thus, statistical representations of the surface topography and interfacial forces need to be integrated with nanotribological measurements to develop more widely applicable and predictive tools. 

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