Boundary Lubrication Polymers

A considerable number of experimental extensions have been developed in recent years. Luckliam et al [5] and Dan [ ] review examples of dynamic measurements in the SFA. Studying the visco-elastic response of surfactant films [ ] or adsorbed polymers [7, 9] promises to yield new insights into molecular mechanisms of frictional energy loss in boundary-lubricated systems [28, 70]. 

In summary, for metal surfaces in boundary lubrication, complex tribochemical reactions occur along with the physical/chemical adsorptions, which lead to the formation of surface hlms, consisting of reaction products, oxide layer, the mixture of particles and organometallic polymer, and perhaps a viscous layer. The surface hlms operate as a sacri-... 

The work function of the rubbing surfaces and the electron affinity of additives are interconnected on the molecular level. This mechanism has been discussed in terms of tribopolymerization models as a general approach to boundary lubrication (Kajdas 1994, 2001). To evaluate the validity of the anion-radical mechanism, two metal systems were investigated, a hard steel ball on a softer steel plate and a hard ball on an aluminum plate. Both metal plates emit electrons under friction, but aluminum produced more exoelectrons than steel. With aluminum, the addition of 1% styrene to the hexadecane lubricating fluid reduced the wear volume of the plate by over 65%. This effect considerably predominates that of steel on steel. Friction initiates polymerization of styrene, and this polymer formation was proven. It was also found that lauryl methacrylate, diallyl phthalate, and vinyl acetate reduced wear in an aluminum pin-on-disc test by 60-80% (Kajdas 1994). 

Wear is defined as the loss of material from a surface as the result of relative motion. In this chapter, the wear processes in polymer implants are discussed. Polymers are used in a wide variety of implants in the human body such as joint replacement implants, pacemakers, catheters and heart valves. Wear of polymer implants is almost exclusive to joint replacement implants, such as those used to replace the hip or knee. These implants involve the articulation of a metal or ceramic against a polymer. Typically these implants operate with a mixed or boundary lubrication regime and, therefore, there is contact between the bearing surfaces that can lead to the generation of wear debris. The chapter is divided into sections that cover implants, wear processes, polymers used in implants, the effect of wear debris on the body and, finally, likely future trends. 

The effectiveness of boundary lubrication by PLL(10)-g[2.9]-PEG(2) in aqueous buffer solution is very apparent in relatively low velocity regimes, where lubrication by water alone is practically impossible due to its extremely low pressure-coefficient of viscosity and poor film-forming properties. The relative adsorption behavior of the polymer onto SiO,t and FeO surfaces, as investigated by OWLS ( 120ng/cm for SiO and 60 ng/cm for FeO,t surfaces), seems to explain the relatively less effective lubrication for FeO /FeOx compared with the FeO t/SiO t tribo-pair. In summary, the PLL(10)-g[2.9]-PEG(2) appears to form a protective layer both on silicon oxide and iron oxide surfaces, thus effectively improving load-carrying and boundary lubrication properties of water for a variety of dynamic contact regimes. 

KEY WORDS poly L-lysine)-g-poly ethylene glycol) (P X-g-P Q), aqueous lubrication, polymer architecture, boundary... 

As shown above, the polymer PLL- -PEG functions in aqueous solution as an effective boundary-lubricating additive and this effectiveness depend upon the polymer architecture. The focus of this discussion is to consider the mechanism of this boundary-lubricating performance and thus to determine how the polymer... 

In summary, we expect that strongly attached po electrolyte brushes hold great potential as effective surfaces for aqueous boundary lubrication under low contact pressures. To this end, the controlled polymerization of dense polymer brushes via the employed photopolymerization method is believed to serve as a versatile tool for the specific fabrication of ultralow-fiiction sur ces. 

Keywords Boundary lubrication Aqueous lubrication Glycerol Polymer brushes Viscosity... 

The effect of polymer brushes in different lubrication regimes is seen in Fig. 4a and b, in which the Stribeck curves obtained from pin-on-disk and MTM measurements are plotted, respectively. The coefficient of friction is plotted against speed multiplied by viscosity for all HEPES-glycerol mixtures both in the presence and the absence of the polymer. As expected, the effect of polymer in reducing the friction is predominantly seen in the boundary-lubrication regime. The effect of polymer on the friction is also extended to the mixed-lubrication regime... 

---