Adhesive friction of elastomer

Chernyak YB, Leonov AI (1986) On the theory of the adhesive friction of elastomers. Wear 108 105-138... 

The main objective of this paper is to present a detailed view of various aspects of adhesion and deformation friction based mainly upon the research findings of this laboratory. An attempt is also made to analyse the large number of results reported elsewhere in order to develop a coherent presentation. Certain fundamental aspects of friction are discussed at first from a phenomenological point of view. A discussion of the law of friction relating to motion follows with a study of the stick-slip phenomena. The next part deals with the isothermal adhesive friction of elastomers on nominally flat and smooth surfaces. 

Experimental Investigation of the Effect of Electrical Potential on Adhesive Friction of Elastomers... 

The role of adhesion and surface energetics on polymer friction has been critically examined by Lee. The application of molecular kinetic theory to adhesion and friction of elastomers has been carried out by Lavrentev , and molecular interaction for solids at contact have been reviewed . 

Adhesion and Friction Properties of Elastomers at Macroscopic and Nanoscopic Scales... 

Polymers generally exhibit complex tribological behaviors due to different energy dissipation mechanisms, notably those induced by internal friction (chain movement), which is dependent on both time and temperature. Polymer friction is then governed by interfacial interactions and viscoelastic dissipation mechanisms that are operative in the interfacial region and also in the bulk, especially in the case of soft materials. Friction of a polymer can be closely linked to its molecular structure. The role of chain mobility has been studied in the case of elastomers, based on dissipation phenomena during adhesion and friction processes of the elastomer in contact with a silicon wafer covered by a grafted layer [1-5]. 

The adhesion component of the unlubricated sliding friction for an elastomer may be expressed in terms of tan 6, the loss angle ... 

The analysis makes use of relaxation and retardation spectra of elastomers. The estimation of the magnitude of friction has not yet been attempted. However, a major step towards that goal has been shown. In particular the wetting theory has been found to be useful in describing the strength of a countersurface in adhesion. 

New methods based on the contact mechanics technique promise to make it possible to measure simultaneously the work of adhesion, area of contact, and normal and lateral forces between two elastomer surfaces and thus offer the possibility of providing new insights on microscopic mechanisms of friction, adhesion, and wear. 

When the water film is squeezed out, the thick water layer is removed and the surfaces are separated by lubricant film of only molecular dimensions. Under these conditions, which are referred to as BL conditions, the very thin film of water is bonded to the substrate by very strong molecular adhesion forces and it has obviously lost its bulk fluid properties. The bulk viscosity of the water plays little or no part in the frictional behavior, which is influenced by the nature of the underlying surface. By comparing with the friction force of an elastomer sliding on a rigid surface in a dry state, Moore was able to conclude that for an elastomer sliding on a rigid surface under BL conditions, one can expect ... 

Today it is claimed that the surface fluorination of polymers using F2 gas mixtures enhances a wide range of properties, e.g., low permeability to nonpolar liquids4 improved permselectivity,5-6 excellent wettability and adhesion,7 low friction coefficient (especially for elastomers),8 and chemical inertness.9 Obviously, these properties depend on the chemical composition ofthe fluorinated layer, which in turn is determined by the chemical structure ofthe base polymer, the composition of the F2 gas mixture, and the fluorination parameters. 

The triblock copolymers exhibit increasing friction with increasing slide rate (111). Under high-slide rates, frictional work heats the surface of the shoe soles up to the glass transition of the hard block, about 75°C as it appears in commercial materials. Only the surface 40 to 50 nm or so need to be heated. Above the glass transition temperature of the hard block, the elastomer temporarily becomes an adhesive note Section 8.13. By contrast, chemically cross-linked homopolymer elastomers may shred at high-sUde rates, reducing their coefficient of friction. 

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