Lubricants interaction with surfaces

In the absence of mechanical activation, the XPS spectrum is different from that obtained in the presence of mechanical activation. Thus, sulfur compounds that are formed on the surface (162 eV) appear in the spectra that are not present in the spectra for static immersion. Cutting produces a change in the surface chemistry and the reaction product formed appears to be similar to that obtained by mechanical activation. Thus, mechanical activity plus increased surface temperatures on a solid surface tend to promote surface chemical reactions. A lubricant interacting with metal oxide can produce entirely different reaction products from that of a lubricant interacting with rubbing metal surfaces. 

The lubricant dynamics can alter the nanoscale aerodynamics of the slider. Conversely, the lubricant morphology and dynamics may be altered because of the presence of the slider. For these types of applications, a molecule-level understanding of the lubricant interaction with nanoscale airbearing and solid surfaces is critical. The HDD industry must cope with problems of lubricant film uniformity, roughness [5], durability [6], and stability [7] in order to achieve its goal of increasing areal density. 

Abstract Aqueous biocompatible tribosystems are desirable for a variety of tissue-contacting medical devices. L-3,4-dihydroxyphenylalanine (DOPA) and lysine (K) peptide mimics of mussel adhesive proteins strongly interact with surfaces and may be useful for surface attachment of lubricating polymers in tribosystems. Here, we describe a significant improvement in lubrication properties of poly (dimethylsiloxane) (PDMS) surfaces when modified with PEG-DOPA-K. Surfaces were characterized by optical and atomic force microscopy, contact angle, PM-IRRAS, and X-ray photoelectron spectroscopy. Sudi surfaces, tested over the course of 200 rotations ( 8 m in length), maintained an extremely low friction coefficient (p) (0.03 0.00) compared to bare PDMS (0.98 0.02). These results indicate... 

Greenberg et al. compared the effects of IF addition in oil under three lubrication regimes hydrodynamics, mixed and limit [44]. They based the lubrication mechanism of IF on a film formation on surfaces and showed that the IF are most effective at mixed Inbrication because all conditions for a good efficiency of IF are combined, hi the hydrodynamic regime, fullerenes do not have interactions with surfaces. In a boundary Inbrication regime, film formed on surfaces is quickly removed, due to contact severity. 

Metal oxides have surface sites which are acidic, basic, or both and these characteristics control important properties such as lubrication, adhesion, and corrosion. Some of the newer infrared techniques such as lazer-Raman and Fourier transform infrared reflection spectroscopy are important tools for assessing just how organic acids and bases interact with the oxide films on metal surfaces. Illustrations are given for the adsorption of acidic organic species onto aluminum or iron surfaces, using Fourier transform infrared reflection spectroscopy. 

The basic processes of dissolution, acid-base interaction, micellization, solubilization, oxidation and reduction take place in oil formulation. During engine operation, additives of the lubricant interact continuously with engine surfaces and themselves. Thus, there is a progressive change in the surface due to the lubrication, friction, and wearing processes, tribofilm formation, and oxidation. All these processes are presented and discussed throughout this book. Surfactant additives are fundamental to reverse micelles (RMs) formation in oil... 

It has been recognized for many years that films on solid surfaces can influence the mechanical behavior of a solid. Mechanical activation gives rise to the input of a considerable quantity of energy at the surface. This energy can produce a number of changes in the nature of the solid surfaces and the lubricant additives that interact with the solid surface to provide a very stable surface tribofilm (see Table 5.6)... 

X-ray Photoelectron Spectroscopy (XPS) tests were conducted on surfaces lubricated with a sulfur-containing extreme pressure additive, dibenzyl sulfide (Baldwin, 1976 Bird and Galvin, 1976). The films can arise from the use of additives that contain sulfur, phosphorus, chlorine, bromine, or boron and the differences in reactivity are affected by the formation of protective layers. Triboinduced electrons are said to activate the formation of iron halides, iron phosphates and iron sulfides (Dorison and Ludema, 1985 Grunberg, 1966 Kajdas, 2001 McFadden et al., 1998 ). When a chemical reaction takes place, e.g., oxygen interacts with aluminum to form aluminum oxide, a large oxygen peak is seen at approximately 500 eV in the Auger electron spectra (Benndorf et al., 1977 Nakayama et al., 1995). 

Friction, abrasion and wear, for instance, are - mathematically - "operators" of a system, i.e. they depend on the parameters of a system, such as the geometry of the surface, the temperature, the load, the relative velocities, the composition of the environmental atmosphere, etc. The operational character of wear, for example, depends on the physicochemical interaction of surfaces and on their interaction with the lubricant and the atmosphere. 

The yield stress of a foam depends to a considerable extent on the character of foam interaction with the tube walls or the cylindrical surface of the viscometer, used in the study of its rheological properties. At low flow rates and smooth tube walls the maximum shear stress of the foam layers contacting the wall can be less than the shear stress of the foam matrix (shear of bubble layers). Hence, the foam flow will occur as a movement of a continuous medium in a cylinder covered with a thin lubricating layer of thickness 2-10 pm [9,16], In this case t0 is ca. 1 Pa, that is, much less than its theoretical value. 

The large size of the hyaluronic acid molecules and their random-coil configuration lead to molecular interactions, even in dilute solution. As a result of these interactions, solutions of the polymer exhibit non-Newtonian and elastoviscosity (Bll). Synovial fiuid shows an increase in viscosity with reduced shearing force and possesses structural rigidity which is reversibly broken down by shearing. Such viscosity behavior makes synovial fluid an ideal lubricant between joint surfaces, which move slowly under considerable pressure for most of the time but which may be required to accelerate violently (03). 

The application of polymer affects choice of filler. For example, to prepare conductive materials, special fillers must be used to obtain the required properties. Also, the method of processing imposes certain constraints on the choice and treatment of the filler before its use. For example, polymers processed at high temperature require fillers which do not contain moisture. This affects both the choice of the filler and/or its pretreatment. The choice of additives used to improve the incorporation of the filler depends on the application and the properties required from a product but it is also determined by the processing method. For example, the viscosity of a melt is reduced by special lubricating agents whereas the viscosity of filler dispersions is controlled by the surface treatment of filler. In some cases, the order of addition is important or a special filler pretreatment is used to achieve the desired results. These methods are discussed in special section in the table. Some fillers simply caimot be used with some polymers. In other cases, special care must be taken to ensure polymer stability or filler may interact with some vital components of the formulation. This subject is discussed in special considerations of filler choice. 

The effect of polymer brushes on the reduction of sliding friction was also observed for solid friction, using surface force apparatus (SEA) measurements [83-86]. For example, Klein et al. reported a massive lubrication between mica surfaces modified by repulsive polyelectrolyte brushes in water [83]. These results show that polymer dangling chains on solid or gel surfaces can dramatically reduce the surface friction if the polymer brush has a repulsive interaction with the sliding substrate. 

The free hydroxyl group in ricinoleic acid is able to interact with polar groups on metal surfaces, thereby giving superior lubricity. The largely mono-ene nature of castor oil gives it low-temperature fluidity without the loss of oxidative stability of polyunsaturates. Castor oil is used in specialist two-stroke applications and can be modified for use in greases. 

In boundary lubrication, solid surfaces are so close together that appreciable contact between opposing asperities is possible. Under these conditions, friction and wear are determined predominantly by interactions between the solid and the liquid phases [15]. The chemistry of friction surfaces and their state therefore determine their interaction with the lubricant components. However, this type of interaction, especially in industrial tribological systems, is very complex and difficult to explain, even applying the most modern analytical techniques. 

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