Adhesive friction

Yoshizawa H, Chen Y L and Israelachvili J N 1993 Recent advances in molecular level understanding of adhesion, friction and lubrication Wear 6B 161-6... 

The tenn tribology translates literally into the study of nibbing . In modem parlance this field is held to include four phenomena adhesion, friction, lubrication and wear. For the most part these are phenomena that occur between pairs of solid surfaces in contact with one another or separated by a thin fluid film. Adhesion describes the resistance to separation of two surfaces in contact to while friction describes their tendency to resist shearing. Lubrication is the phenomenon of friction reduction by the presence of a fluid (or solid) film between two surfaces. Finally, w>ear describes the irreversible damage or defonnation that occurs as a result of shearing or separation. 

Noy, A., Frisbie, C.D., Rozsnyai, L.F., Wrighton, M.S. and Lieber, C.M., Chemical force microscopy — exploiting chemically modified tips to quantify adhesion, friction, and functional-group distributions in molecular assemblies. J. Am. Chem. Soc., 117(30), 7943-7951 (1995). 

Israelachvili, J. N., Adhesion, Friction and Lubrication of Molecularly Smooth Surfaces, Fundamentals of Friction, I. L. Singer and H. M. PoUock, Eds., Kluwer Academic Publishers, 1991,PP-351-385. 

On the dusted track the diminished adhesion friction component is clearly apparent for all three rabbers when comparing them with the master curves on the clean track The friction plateau observed for the rubbers filled with 50 pphr black which is typical for tire tread compounds is observed for most rubbers, as shown in Figure 26.5. 

When forces are transmitted, slip occurs because the wheel is being deformed. The relation between force and slip is one of the most important laws in tire mechanics, because it influences the all important properties of traction, durability, and tire wear. (This is not only true for tires, but also for all force transmission by adhesion friction). 

It was pointed out in Section 26.2.1 that the friction coefficient is considerably larger on a rough track than on a smooth one when the log ajv values of the master curve are small, i.e., when the temperature is high, and the speed is low, i.e., when the viscoelastic losses are low. Moreover, the adhesion friction, which enables tangential stresses to be built up, is low. 

Chapter 1 is a view of the potential of surface forces apparatus (SFA) measurements of two-dimensional organized ensembles at solid-liquid interfaces. At this level, information is acquired that is not available at the scale of single molecules. Chapter 2 describes the measurement of surface interactions that occur between and within nanosized surface structures—interfacial forces responsible for adhesion, friction, and recognition. 

For example a polymer s interfacial characteristics determine chemical and physical properties such as permeability, wettability, adhesion, friction, wear and biocompatibility. " However polymers frequently lack the optimum surface properties for these applications. Consequently surface modification techniques have become increasingly desirable in technological applications of polymers. - ... 

Paint and printing adhesion friction Oil and gas production Oil spill... 

Most solids return to their original volume when they have parted with the caloric which caused the distan-tion of their particles some, however, are incapable of doing so, and are permanently elongated or enlarged every time they are subjected to the influence of a high temperature. Such is the case, more especially, with zinc and lead—the particles of which, in sliding over each other, are supposed to possess an amount of adhesive friction which prevents their retraction to the full extent they had expanded. 

Friction of rubber is a very complicated phenomenon but is generally thought of as being composed of two parts, adhesive friction and hysteresis... 

In spite of the apparent sensitivity to the material properties, the direct assignment of the phase contrast to variation in the chemical composition or a specific property of the surface is hardly possible. Considerable difficulties for theoretical examination of the tapping mode result from several factors (i) the abrupt transition from an attractive force regime to strong repulsion which acts for a short moment of the oscillation period, (ii) localisation of the tip-sample interaction in a nanoscopic contact area, (iii) the non-linear variation of both attractive forces and mechanical compliance in the repulsive regime, and (iv) the interdependence of the material properties (viscoelasticity, adhesion, friction) and scanning parameters (amplitude, frequency, cantilever position). The interpretation of the phase and amplitude images becomes especially intricate for viscoelastic polymers. 

Micromechanical experiments made so far can be roughly divided into two parts (i) design of special techniques to measure and evaluate separately different contributions in the net force, such as adhesion, friction, deformation, and (ii) imaging of various heterogeneous surfaces such as blends, composites and microphase separated structures by conventional SFM s to collect statistical information and understand the origin of the mechanical contrast. Many of the micromechanical experiments were discussed elsewhere [58, 67, 68, 381, 412-414]. Here we will focus on recent advances in analytical applications of the active probe SFM. 

Concerning properties, SFM has become a unique technique in probing local adhesion, friction and elastic response of various materials. This is based on the ability to measure forces as small as picoNewtons and probe areas well below 100 nm. The peculiar sensitivity of the force probe to different types of static and dynamic interactions provides a great number of contrast mechanisms which can map the surface structure regarding the chemical composition and physical properties. However, in most SFM measurements the interpretation of the surface maps remain to be very intricate, mostly because of the concurrent contribution of different forces into the net force. The progress in this field relies on new developments in technique which would allow to measure the properties like stiffness, adhesion, friction and viscosity, separately. 

Buckley, D.H., Surface Effects in Adhesion, Friction, Wear, and Lubrication, Elsevier, Amsterdam, 1981. 

Houston IE Kim HI, Adhesion friction, and mechanical properties of functionalized alkanethiol self-assembled monolayers, Acc. Chem. Res., 2002, 35, 547-553. 

With respect to screw geometry, we turn back the clock to Wolfen, where the team was searching for the perfect mechanical apparatus for high-viscosity technology. It had to function despite the adhesive, frictional, and antifrictional properties of the product, cope with various material consistencies, and overcome rheological changes caused, for instance, by reactions in the machine. 

Keywords. Polymers, Interfaces, Grafted chains, Adsorbed chains, Polymer brushes, Adhesion, Friction, Chains pull out, Slip at the wall... 

Where one or both of the contacting surfaces becomes permanently deformed during sliding, the energy required to produce the deformation represents an additional component of the friction force. For engineering surfaces the amount of permanent deformation which can be tolerated is very limited so that the deformation friction is small in comparison with the adhesive friction. Elastic deformation only makes a significant contribution to the total friction when there is a high level of hysteresis in the elastic recovery, such as in vehicle tyres, and this is not normally a consideration when molybdenum disulphide is used. For practical purposes it can therefore be assumed that adhesive friction is the only type of friction which needs to be considered. 

It can therefore be accepted that whether it is in the natural crystalline form or in a consolidated film, the friction of molybdenum disulphide is adhesive friction, and its low magnitude is due to the easy shear between adjacent lamellae which is made possible by the unusually favourable crystal and electronic structure. However, it must be remembered that the correct orientation of the crystallites is essential for the maintenance of low friction. The shear strength is low only parallel to the basal plane of the lamellae. In other directions the shear strength is high, so that the coefficient of friction will also be high . ... 

There is some evidence that running-in of a film is improved in the presence of moisture, and this may again be due to the effect of increased friction in removing high spots in an unburnished film. This would in fact be a specific case of the general effect of moisture on film wear, which is to increase wear rate and reduce wear life Both effects are consistent with the effect of moisture in increasing friction, since in general any factor which increases adhesive friction will also tend to increase adhesive wear. 

Use Roofing compounds, hot-melt adhesives, friction tape, sealants, heating oil for large buildings, factories, etc. 

Compositional contrast, as well as modulus, can also be assessed by laterally resolved imaging of normal or lateral forces in the contact mode AFM. In the corresponding mapping [121] (see also Chap. 4), force-displacement curves are recorded for each pixel. Subsequently, the pull-off forces, as a measure for adhesion, and the indentation part of the loading curves, to extract/fit the elastic modulus, are evaluated for each pixel. In particular for adhesion mapping, the use of chemically functionalized AFM probe tips [122], has been shown to be a suitable approach to map chemical composition and functional group distributions down to the sub-50 nm scale [123]. The mapping of adhesion, friction, and surface mechanical properties will be treated in more detail in Chap. 4. 

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