| EPSRC Reference: |
GR/M57118/01 |
| Title: |
ROPA:STUDY OF BOUNDARY LUBRICATING FILMS USING SOFT- FILM SCANNING PROBE MICROSCOPY |
| Principal Investigator: |
Spikes, Professor HA |
| Other Investigators: |
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| Department: |
Mechanical Engineering |
| Organisation: |
Imperial College London |
| Scheme: |
ROPA |
| Starts: |
01 September 1999 |
Ends: |
31 August 2001 |
Value (£): |
107,747
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| EPSRC Research Topic Classifications: |
| Eng. Dynamics & Tribology |
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| No relevance to Underpinning Sectors |
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Summary on Grant Application Form |
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Soft-film, scanning probe microscopy will be used to investigate the structural and physical characteristics of oil-immersed boundary films formed in rubbing contacts. Films formed by grease, antiwear additives and adsorbed viscosity-modifier polymers will be investigated. The results will be compared with film thickness and friction measurements on the same systems to increase our understanding of the nature and properties of boundary lubricating films.In recent years, growing concern for low friction and thus energy-saving in machine components has led to a general reduction in lubricant viscosities employed and also an increase in operating temperatures. Both of these trends have placed greater reliance on the presence of effective boundary lubricating films, which has focused attention upon understanding the origins and properties of these films.Boundary films are formed by the direct chemical and/or physical interaction of components of a liquid lubricant with rubbing solid (usually metal) surfaces. For many years, these films were envisaged as molecularly thin, solid-like layers. However it is now recognised that the span of boundary film types is very broad, ranging from solid-like monolayers to much thicker (10 to 100nm) semi-solid, viscous or elastoplastic coatings. Typical examples include phosphate/borate glasses 10-50nm thick formed by antiwear additives (1), deposited metal soaps 2-20nm thick formed by some friction modifier additives (2), complex deposited soap/oil films 50-1000nm thick formed by greases (3) and viscous layers 10-30nm thick formed by adsorption of some viscosity index improper polymers from solution (4)It is of both fundamental and practical importance to be able to characterise the physical and chemical properties of such boundary films, since they play important roles in controlling friction and wear. One practical problem is that they are all formed and function at relatively high temperatures within a liquid lubricant environment. This means that classical vacuum-based surface analysis techniques, which require cooling and solvent rinsing, are not well-suited to their investigation. The most successful techniques employed to study boundary lubricating films have therefore been force balance (5), ultrathin film interferometry (6), in and out-of contact vibrational spectroscopy (7) and near edge x-ray diffraction methods (8). These have enabled the chemical composition and overall thickness of boundary lubricating films to be determined but have not been able to characterise their physical properties and distribution under realistic contact conditions.One group of experimental techniques which has considerable potential for studying boundary films are those based on scanning nanoprobes, including atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). These are able, in principle, to probe solid surfaces immersed in supernatant liquid and the applicant has successfully employed AFM to map the topography and friction properties of surfaces in lubricant environments (9). Except for this work, surprisingly little published work has employed nanoprobes systematically to study immersed lubricant additive films, although valuable work has been carried out on simple liquids (10). In the last two years, the ability of AFM to characterise surface films has been greatly enhanced with the development of techniques able to detect and measure some of the properties of very thin, relatively soft layers on solid surfaces. These techniques come under a variety of names and guises depending upon the instrument manufacturer concerned, including modulated force imaging , nodding mode , layered imaging and intermittent contact mode . All relay upon varying the nanoprobe tip displacement in a controlled fashion at a series of positions across a surface, by applying a force either to the tip support cantilever or directly to the tip, and measuring one or more features of the result
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Key Findings |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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Potential use in non-academic contexts |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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Impacts |
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| Description |
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk |
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Sectors submitted by the Researcher |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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| Project URL: |
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| Further Information: |
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| Organisation Website: |
http://www.imperial.ac.uk |