Temperature dependence of friction

Temperature dependence of friction and wear of some heat resistant polymers was studied. Except the one filled with glass fibers of kO wt. PPS, the specimen polymers were unfilled. 

FIGURE 7.13 Temperature dependence of friction of CHjfCH inSH is shown as a plot of the slope of the friction signal as a function of the coefficient of friction vs. temperature [87]. (From Ohzono, T., and Fujihira, M. 2000. Phys. Rev. B 62 17055. With permission.)... 

Figure 6, Temperature dependence of friction on 20-nm films ofPMMA, PET, and...

The temperature dependence of friction on a PMMA film is shown in Figure 4. "Friction difference (trace - retrace) images are displayed for 3 temperatures 50°C, 90 C, and 110 C (Figure 4a). All three images have the same Z (fnction) scale and... 

Results of friction tests performed on a friction machine of type-147 indicate applicability of XPS to solving tribological problems of UHMWPE. Figure 11 shows temperature dependence of frictional heating of UHMWPE plate on the treatment temperature with SC-CO. One can see the gradual decrease of frictional heating with increasing temperature SC-CO till 85°C, and as it follows from the XPS data, the sharp rise since 100°C. 

K.A. Grosch, The speed and temperature dependence of rubber friction and its bearing on the skid resistance of tires. The Physics of Tire Traction, Theory and Experiment. D.L. Hayes and A.L. Browne (eds.). Plenum Press, New York/London, 1974, 143. 

An example of the velocity dependence of friction is given in Figure 5 for a boundary lubricant confined between two incommensurate surfaces.25 For the given choice of normal pressure and temperature, one finds four decades in sliding velocity for which Eq. [7] provides a reasonably accurate description. 

Fig. 3.8 Temperature dependence of the monomeric friction coefficients for PEP and PE. The symbols present the NSE results (filled triangle PEP, filled circle PE). The solid lines display the respective rheological predictions extrapolations are shown as dashed lines (solid lines prediction [51],point dashed line prediction [34] for PEP)...

Fig. 4.35 Right-hand side Monomeric friction coefficients derived from the viscosity measurements on PB [205]. The open and solid symbols denote results obtained from different molecular weights. Solid line is the result of a power-law fit. Dashed line is the Vogel-Fulcher parametrization following [205]. Left hand side Temperature dependence of the non-ergodicity parameter. The three symbols display results from three different independent experimental runs. Solid line is the result of a fit with (Eq. 4.37) (Reprinted with permission from [204]. Copyright 1990 The American Physical Society)...

The temperature dependence of the friction coefficient of poly(acrylamide) gel was studied at two different concentrations of acrylamide (AAm) and N,N -methylenebisacrylamide (Bis) AAm Bis = 1.24 M 22.4 mM and AAm Bis = 693 mM 7 mM. The weight concentrations of these sample gels was about 8.8 and 5 wt.%, respectively. The composition of the latter gel is almost the same as the composition typically recommended for acrylamide gel electrophoresis. The friction coefficient of these gels was measured at a fixed pressure of 5.88 x 103 Pa, which corresponds to 60 cm of the height of the water column. The temperature was varied from about 0 to 60 °C. 

Fig. 6. The temperature dependence of the friction coefficient of the poly( acrylamide) gels. The total concentrations of acrylamide are 1.24 M (8.8% mass fraction), and 693 mM (5% mass fraction), respectively. Open symbols are used for the results obtained in the cooling process and closed symbols represent the results taken upon increasing the temperature. In the upper part of this figure, the temperature dependence of the ratio f(T)/rj T) is shown. The values of the viscosity are taken from a table. Symbols are the same as those used in the raw value of the friction coefficient...

Here, both the viscosity of water and the correlation length of the gel are a function of the temperature. Therefore, in order to discuss the temperature dependence of the correlation length of the gel, it is convenient to use the ratio f(T) /r (T) rather than the raw value of the friction coefficient f(T) since the ratio directly represents the effective size of the pores and their distribution. 

The temperature dependence of the friction coefficient of poly(acrylamide) gels are analyzed according to the above equation. In our analysis, the values of the viscosity of water is taken from the table. The results thus obtained are also shown in Fig. 6. It can be seen from this figure that the friction of the poly(acrylamide) gel normalized with the viscosity of water is independent of the temperature. It indicates that the pore size of the poly(acrylamide) gel is stable in the temperature range studied. 

The temperature dependence of the friction coefficient normalized by the viscosity of the water, f/rj, is given in Fig. 10. The solid symbols are used in the increasing of the temperature and the open symbols are used in the lowering of the temperature. The values of the viscosity of the water, tj(T), are taken from the literature. For the chemically cross-linked gels, such as the poly(acrylamide) gel, the friction, f/rj, is independent of the temperature which has been already shown in previous section. It is, however, found from this figure that the friction... 

Fig. 10. The temperature dependence of the friction coefficient f of polyfiV-isopropylacrylamide) gel normalized by the viscosity of water T - Solid circles are used in the increasing of the temperature and open circles are used for the lowering of the temperature...

In practical applications, the increase of viscous friction with speed is often lower than expected from Eq. (11.9). The explanation is that friction leads to an increased temperature of the lubricant which reduces the viscosity. For most lubricants the temperature dependence of the viscosity is given by... 

At much higher temperatures, where CDCs are able to develop, one has a temperature dependence of ocdc> which involves both oy2 and the monomeric friction coefficient, f. In systems where the activation energy of f is high enough, its temperature dependence can lead to a steeper decrease of ctcdc with increasing temperature than for ay. For such polymers, at temperatures not much lower than Ta, CDCs can be the favoured micromechanism and a SDZ-CDC transition will take place. 

A few comments on (2.27), (2.29), and (1.12) are appropriate at this point. The activation energy in the Arrhenius region is independent of 17, since friction changes only the velocity at which a classical particle crosses the barrier and thus affects only the preexponential factor. However, friction reduces both kc and Tc and thereby widens the Arrhenius region. Dissipation has a noticeable effect on the temperature dependence of... 

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