Friction of polymer

Slip and friction of polymer melt flows N. El Kissi, J-M. Rau... 

Since dynamic friction of polymers has a large contribution from internal viscoelastic dissipation, plots of the friction force, determined, e.g., by AFM, vs./D are qualitatively similar to plots of tan<5 vs. fa. Hence, by measuring dynamic friction forces under well-controlled conditions, the dynamics of a given polymer can be directly probed at the free surface of a sample specimen. Thereby surface vs. bulk properties can be probed as well as confinement effects. 

Contact during and after CMP is between a wafer and a polymer as a pad or brush thus the nature of the contact is predominantly elastic. As we saw in Section 2.1, the ratio of the elastic modulus E and the hardness H determines the extent of the plasticity in the contact region as well as the surface topography. For metals, E/H is typically 100 or greater, whereas for many of the softer polymers (low P s), E/H is only about 10. Thus the contact between metals and polymers is almost completely elastic except against very rough surfaces. Another factor that affects the friction of polymers is the strong time dependence of their mechanical properties most polymers are viscoelastic and also show a marked increase of flow stress with strain rate. 

The friction of polymers or CMP processes can be attributed to two major sources in mixed modes deformation involving the dissipation of energy in quite a large volume around the local area of contact, and adhesion originating from the interface between the wafer and the pads (brush). The details of the deformation and adhesion will be discussed in Chapter 5, along with a clear schematic illustration. 

CZlCHOS Contact Deformation and Static Friction of Polymers... 

Figure 17. Friction of polymer/polymer pairs (PTFE, POM, PA66, PP against ANS).

Erhard, G. "Sliding Friction of Polymer-Polymer Pairs" (in German), Jahrbuch VDI-Ges. Werkstoff-technik (Dtisseldorf), 1981 7. 

Friction of Polymer Pins Sliding Against Steel Disk. Figures 16(a) and (b) show variations of the coefficients of friction of variotis polymers with disk temperature in the steady state of friction and at the initial stage of sliding, respectively. It may be assmed that friction in the steady state corresponds approximately to the friction between the polymers and their transferred layer while the initial friction indicates that between the polymers and steel disk. Except for PPS, the initial friction is considerably lower than steady-state friction in temnerature ranges below a certain critical temperature which depends upon the type of polymer. The critical temperature is approximately 60, lUO, 150 and 150 C, for PI, PAI, PEEK and PES, respectively. For PPS, the coefficient of initial friction is about... 

Polyimide friction. The friction of polymers consists of an adhesion component and a deformation component. The adhesion component arises from the shearing of adhered junctions and is usually modeled as the product of the real area of contact and the shear strength of the polymer. The deformation component arises from the frictional work required to balance the energy dissipated in plastic deformation. Some Investigators have developed friction models in which the adhesive bonds at the junctions Increase the amount of plastic deformation over that which would exist in the absence of these bonds (13). 

B. Briscoe, Friction of Polymers in Friction and Traction , ed. D. Dowson et aU Westbury Press, London, 1981. 

Briscoe, B.J. "Friction of Polymers" in Fundamentals of Friction Macroscopic Origins , Eds. E. Singer and H. Pollack, Kluwer Academic Press, Netherlands, 1992. 

In general the coefficient of friction of polymer pellets against a steel surface will rise with increasing temperature, although the results in Table 6.1 show no significant rise up to 120 °C. The fall between 60 and 100 °C may be a rubbing-in characteristic of the instrument. 

Adhesion in the Friction of Rubber-like Polymers Theories of Rubber Friction Adhesion in the Friction of Polymers The Effect of Pressures Effect of Speed and Temperature The Interfacial Layer Boundary Lubrication... 

We turn to the part that adhesion plays in the friction of polymers. It now becomes desirable to treat rubber-like materials under one heading and polymers below their glass transition temperature under another. 

With unlubricated surfaces there is general agreement with the view that the adhesion component is responsible for the major part of the friction of polymers. The adhesion component is not, of course, a constant but depends on speed, temperature and contact pressure in a manner suggesting a close correlation with bulk viscoelastic properties. This appears to be reasonably valid for rubbers but not... 

Originally, rol1-formation was proposed by Reznikovskii and Brodskii to be limited to high elastic materials. New evidence shows that sliding friction of polymers with varying degrees of ductivity can also undergo roll formation. Furthermore, polymers usually considered to be brittle at room temperature can be ductile under load (20 to 30 Kg/cm ) about 80° under their Tg s. 

Adhesion and Deformation Friction of Polymer on Hard Solids... 

Hitherto, the discussion referred to the details of the mechanism of friction of elastic bodies. In friction of polymers, it is necessary to consider the viscoelastic properties of the materials. 

In order to minimize complications, most of the studies describe the friction of polymers on hard solids. The friction-speed relation then, displays the influence of the viscoelastic properties of the polymer. The hard solid countersurfaces have usually been steel and glass. 

V. A. Belyi et al.. Friction of Polymers [Russian Nanka Moscow 1972. ... 

J. J. Bikerman As long as no excessive speeds or loads are used, sliding friction of polymers without wear readily occurs for long periods of time. 

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