Publications
134 results found
Hili J, Pelletier C, Jacobs L, et al., 2018, High-Speed Elastohydrodynamic Lubrication by a Dilute Oil-in-Water Emulsion, Tribology Transactions, Vol: 61, Pages: 287-294, ISSN: 1040-2004
When a concentrated contact is lubricated at low speed by an oil-in-water emulsion, a film of pure oil typically separates the surfaces (stage 1). At higher speeds, starvation occurs (stage 2) and the film is thinner than would be expected if lubricated by neat oil. However, at the very highest speeds, film thickness increases again (stage 3), though little is known for certain about either the film composition or the mechanism of lubrication, despite some theoretical speculation. In this article, we report the film thickness in a ball-on-flat contact, lubricated by an oil-in-water emulsion, at speeds of up to 20 m/s, measured using a new high-speed test rig. We also investigated the sliding traction and the phase composition of the film, using fluorescent and infrared microscopy techniques. Results show that, as the speed is increased, starvation is followed by a progressive change in film composition, from pure oil to mostly water. At the highest speeds, a film builds up that has a phase composition similar to the bulk emulsion. This tends to support the “microemulsion” view rather than the “dynamic concentration” theory.
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Lu J, Reddyhoff T, Dini D, 2017, 3D Measurements of Lubricant and Surface Temperatures Within an Elastohydrodynamic Contact, Tribology Letters, Vol: 66, ISSN: 1023-8883
We present an infrared microscopy technique, capable of measuring the temperature of both the bounding surfaces and the oil film in an elastohydrodynamic contact. This technique can, for the first time, spatially resolve the oil film temperature in three dimensions. The contact is produced by loading a steel ball against a sapphire disc, and the film is viewed using an infrared microscope focussing through the disc. Two band pass filters are used to isolate the radiation from the oil film, and Planck’s law is applied to data obtained at a known temperature as part of the calibration procedure. The proposed technique requires the emissivity of the oil film to be measured, which is acquired in situ and is shown to vary strongly as a function of thickness and temperature. The technique is validated under pure rolling conditions, when the temperature of the oil film is equal to the controlled lubricant reservoir temperature, and also compared to an equation commonly used to predict average film temperatures, confirming the value of the unknown constant. The technique is then used to gain insights into the thermal/rheological behaviour within a contact. This is important since the temperature of elastohydrodynamic contacts is critical in determining friction and hence the efficiency of machine components and this technique enables much needed validation and provides input data for CFD and numerical simulations.
Vladescu S, Ciniero A, Tufail K, et al., 2017, Looking into a laser textured piston ring-liner contact, Tribology International, Vol: 115, Pages: 140-153, ISSN: 1879-2464
This paper presents an experimental study into the flow behaviour of lubricant in a reciprocating contact simulating a piston ring–cylinder liner pair. The aim was to understand the effects of cavitation, starvation and surface texture, as well as the interaction between these, in order to improve automotive engine performance. A custom-built test rig was used, in which a section of piston ring is loaded against a reciprocating, laser-textured, fused silica pad representing the liner. A fluorescence microscope focusses through the silica specimen onto the contact in order to image the distribution of dyed oil. Tests were performed using a range of texture geometries and orientations, under starved and fully-flooded lubrication conditions, with measurements being compared against those from a non-textured reference.Under limited oil supply conditions, the non-textured reciprocating contact sweeps oil towards the reversal points (TDC and BDC), leading to starvation and increased friction. This issue is alleviated by the presence of surface texturing, with each pocket transferring oil from the inlet to the outlet of the contact as it passes; the result being 33% lower friction and oil distributed evenly over the liner surface. Even under fully flooded conditions, starvation is shown to occur following each reversal, as the change in sliding direction causes the cavitated outlet to become the oil-deprived inlet. This proof of cavitation-reversal-starvation, which occurs for up to the first 5% of the stroke length, depending on the lubricant’s viscosity, corresponds to regions of high wear, measured in this study and on actual cylinder liners reported in the literature. This process is also counteracted by the presence of surface texture, with each pocket depositing oil into the cavitated region prior to reversal.Fluorescence data also provides insights into other mechanisms with which different textures geometries control friction. Grooves oriented parallel
Vlădescu S-C, Ciniero A, Tufail K, et al., 2017, Optimisation of Pocket Geometry for Friction Reduction in Piston-Liner Contacts, Tribology Transactions, Pages: 00-00, ISSN: 1040-2004
ciniero A, Le-Rouzic J, Reddyhoff T, 2017, The Use of Triboemission Imaging and Charge Measurements to Study DLC Coating Failure, Coatings, Vol: 7, ISSN: 2079-6412
We present a study on the simultaneous evolution of the electron emission and surface charge accumulation that occurs during scratching tests in order to monitor coating failure. Steel discs coated with a diamond-like-carbon (DLC) film were scratched in both vacuum (~10−5 Torr) and atmospheric conditions, with electron emission and surface charge being measured by a system of microchannel plates and an electrometer, respectively. The results highlight a positive correlation between emission intensity values, surface charge measurements and surface damage topography, suggesting the effective use of these techniques to monitor coating wear in real time.
Ciniero A, Le Rouzic J, Baikie I, et al., 2017, The origins of triboemission - correlating electron emission with surface damage, Wear, Vol: 374-375, Pages: 113-119, ISSN: 0043-1648
Triboemission – i.e. the emission of photons, electrons and other charged particles that arise from a sliding contact – may play a key role in tribochemical processes, such as lubricant degradation. However, the mechanisms that give rise to this type of emission are not well understood. For the first time, we present spatially resolved measurements of electron emission, obtained as a range materials are worn. These are obtained from scratch tests, carried out under vacuum conditions (10−5 Torr), in which microchannel plates coupled to a phosphor screen are used to image electron emission.The results show that electron emission occurs at specific locations on the worn surface and, depending on the conductivity of the material, these sites remain active and decay with a time constant of up to several seconds. SEM images of the worn surface at these sites reveal that either surface fractures or grain defects are present. This suggests that fractoemission mechanisms are at least partially responsible for triboemission (however, the possible contribution of tribocharging mechanisms are also discussed). Specifically, this provides evidence to support the theory that triboemission results from the imbalance of charge on opposing faces of wear cracks and that this generates an electric field sufficient to accelerate molecular fracture products, which then bombard the surface leading to secondary emission.The strong geometric correlation between damage topography and electron emission distributions shows the potential of using this technique to monitoring wear and crack formation in real time and under high (30x) magnification.
Profito FJ, Vladescu S-C, Reddyhoff T, et al., 2017, Experimental validation of a mixed-lubrication regime model for textured piston-ring-liner contacts, Materials Performance and Characterization, Vol: 6, Pages: 112-129, ISSN: 2165-3992
Recent experiments have shown that automotive piston-liner friction may be reduced by up to 50 % if the surface of the liner is laser textured with certain configurations of micro-pockets. It is important to model this behavior to understand and optimize the friction reduction mechanisms that are occurring. However, until now, very few models that predict the lubrication performance of textured surfaces have been successfully validated against experimental data. This is because of the requirement for them to: (1) reproduce experimental configurations with a certain degree of fidelity, (2) conserve mass properly, and (3) account for transient, boundary lubrication conditions. To address this, the current paper presents a comparison between the results from a numerical model, which fulfils these criteria, and an experimental test rig operating under the same conditions. The mathematical modeling is based on the averaged Reynolds’ equation with Patir and Cheng’s flow factors and the p − θ Elrod–Adams mass-conserving cavitation model. Simultaneously to the fluid flow solution, the contact pressures that arise from the asperity interactions are also included into the calculations through the well-known stochastic Greenwood and Tripp model for rough contacts. The experimental data is produced using a reciprocating tribometer, whose contact conditions are closely controlled and accurately mimic those found in an automotive piston–liner conjunction. Data is presented in terms of friction force versus stroke angle, and the similarities and differences between the model and experiment are discussed.
Vladescu S, Reddyhoff T, Olver A, et al., 2017, Bearing interface with recesses to reduce friction, US20170009886 A1
A bearing interface of an apparatus, the apparatus having a first element and a second element configured to move relative to each other during operation of the apparatus, the first element comprising a first bearing surface configured to engage at least a portion of a second bearing surface of the second element thereby defining a contact zone between the first bearing surface and the second bearing surface, the first bearing surface having at least one recess indented into the first bearing surface, wherein the dimension of the recess in ...
Wang P, Zhang J, Spikes HA, et al., 2016, Development of hydrodynamic micro-bearings, 16th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2016), Publisher: IOP Publishing, ISSN: 1742-6588
This paper describes the modelling and testing of mm-scale hydrodynamic bearings which are being developed to improve the efficiency of a cm-scale turbine energy harvester, whose efficiency was previously limited by poorly lubricated commercial jewel-bearings. The bearings were fabricated using DRIE and their performance was assessed using a custom built MEMS tribometer. Results demonstrate that acceptably low friction is achieved when low viscosity liquid lubricants are used in combination with an appropriate choice of friction modifier additive. Further reduction in friction is demonstrated when the step height of bearing is adjusted in accordance with hydrodynamic theory. In parallel with the experiments, hydrodynamic lubricant modelling has been carried out to predict and further optimize film thickness and friction performance. Modelling results are presented and validated against experimental friction data.
Profito FJ, Vladescu S, Reddyhoff, et al., 2016, Transient experimental and modelling studies of laser-textured micro-grooved surfaces with a focus on piston-ring cylinder liner contacts, Tribology International, Vol: 113, Pages: 125-136, ISSN: 1879-2464
This paper presents a comparison between the results from numerical modelling and experiments to shed light on the mechanisms by which surface texture can reduce friction when applied to an automotive cylinder liner. In this configuration, textured features move relative to the piston-liner conjunction and to account for this our approach is to focus on the transient friction response to individual pockets as they pass through, and then leave, the sliding contact. The numerical approach is based on the averaged Reynolds’ equation with the Patir & Cheng’s flow factors and the p-θ Elrod-Adams mass-conserving cavitation model. The contact pressures that arises from the asperity interactions are solved simultaneously to the fluid flow solution using the Greenwood and Tripp method. The experimental data is produced using a pin-on-disc set up, in which laser textured pockets have been applied to the disc specimen. Under certain conditions in the mixed and boundary lubrication regimes, both model and experimental results show i) an increase in friction as the pocket enters the contact, followed by ii) a sharp decrease as the pocket leaves the contact, and then iii) a gradual decay back to the pre-entrainment value. From the evidence obtained for the first time from the proposed combined modelling and experimental investigation conducted under carefully controlled conditions, we suggest that these three stages occur due to the following mechanisms: i) a reduction in fluid pressure due to the increased inlet gap, ii) inlet suction as the cavitated fluid within the pocket draws lubricant into the contact, and iii) film thickness decay as oil is squeezed out of the contact. The interplay of these three mechanisms is shown to control the response of micro-textured surfaces und
wang P, Reddyhoff T, 2016, Wall slip in an EHL contact lubricated with 1-dodecanol, Tribology International, Vol: 113, Pages: 197-205, ISSN: 1879-2464
Astudy was conducted ofthe factors that cause anomalous EHDfilm shapes in 1-dodecanol lubricated contacts –i.e.a thickened central plateau and an exaggerated outlet constriction. This has ledto the hypothesisthat, in the region wherepressuresexceed~0.44 GPa, dodecanol experiences slip, which reduces the average lubricant velocityand causesan elevated film thickness in order to maintain flow continuity. The analysis suggests that slip mustbeoccurringat, or closeto, the faster moving surface, since a discontinuityin the flowmidway through thethickness of the film wouldnot affectthe average speedof the lubricant. Based on this hypothesis, an equation has beenderived to predict the anomalous central film thickness as a function of applied slide-roll ratio and this has beenvalidated by comparison with experimentally measured central film thickness values. Further support of this hypothesis is provided by traction test results showing a discontinuity occurring close tothe onset of slip.
Vladescu S-C, Olver AV, Pegg IG, et al., 2016, Combined friction and wear reduction in a reciprocating contact through laser surface texturing, Wear, Vol: 358-359, Pages: 51-61, ISSN: 0043-1648
Vladescu S-C, Medina S, Olver AV, et al., 2016, The Transient Friction Response of a Laser-Textured, Reciprocating Contact to the Entrainment of Individual Pockets, Tribology Letters, Vol: 62, ISSN: 1573-2711
To shed light on the mechanisms with which surface texture improves the tribological performance of piston–liner contacts, we have measured the transient friction response as individual pockets pass through a reciprocating sliding contact. Tests were performed at different sliding speeds and results compared to those from a non-textured, reference specimen under different lubrication regimes. At low speed when the contact is in the boundary regime, friction force falls abruptly as each pocket leaves the contact zone, before gradually returning to an approximately steady-state value. This suggests that each pocket acts to temporarily increase the film thickness, which then decays to its non-textured value as oil is squeezed out. At higher speeds, friction is seen to reduce in a stepwise fashion, since the period between pockets being entrained is less than the time taken for the film to decay. In addition, friction results obtained when the contact is operating in the middle of the mixed regime point to a temporary film thickness collapse as the pocket enters the contact, and this agrees with recent modelling predictions. At higher speeds, the compound effect of successive pockets is to shift the contact to the right on Stribeck curve. These results imply that each pocket gives rise to an increase in film thickness that is both short-lived and small in magnitude (we estimate a few tens of nm). However, the resulting effect on friction can be significant (up to 82 % in this study) for two reasons: (1) provided the pocket frequency is sufficiently high, each successive pocket entrainment builds the film up without there being time for it to reduce back to its steady-state value; (2) when the contact is in the mixed regime, the Stribeck curve is at its steepest and friction is therefore most sensitive to film thickness changes. This has important practical implications in that pocket spacing on piston liners should be varied as a function of reciprocating sliding
Putignano C, Reddyhoff T, Dini D, 2016, The influence of temperature on viscoelastic friction properties, Tribology International, Vol: 100, Pages: 338-343, ISSN: 0301-679X
Viscoelastic friction strongly depends on temperature, which determines the material stiffness and, therefore, given a constant load, the volume that is deformed and dissipates energy. We compare the results obtained by a numerical approach introduced by Carbone and Putignano (2013) [1] with measurements that separate viscoelastic losses from Coulomb contribution. This is done for a range of temperatures. We show that viscoelastic friction curves for different temperatures can be arranged into a single master curve using a frequency shift coefficient, which can be found from the characterization of the viscoelastic material response. This shows that it is possible to accurately (a) use dynamic material analysis data to extrapolate viscoelastic friction measurements to values outside the tested range, and (b) use a tribometer to obtain fundamental viscoelastic material properties.
Vladescu S, medina S, olver A, et al., 2016, Lubricant film thickness and friction force measurements in a laser surfacetextured reciprocating line contact simulating the piston ring – linerpairing, Tribology International, Vol: 98, Pages: 317-329, ISSN: 1879-2464
Applying surface texture to piston liners may provide an effective means of controlling friction and hence improving engine efficiency. However, little is understood about the mechanisms by which pockets affect friction, primarily because of a lack of reliable experimental measurements. To address this, the influence of surface texture on film thickness and friction force was measured simultaneously in a convergent-divergent bearing, under conditions that closely replicate an automotive piston ring-liner conjunction. Film thicknesses were measured using a modified version of the ultra-thin film optical interferometry approach, enabling film thicknesses <50 nanometres to be measured under transient, mixed lubrication conditions. This involved using the out-of-contact curvature of the specimens in place of a spacer layer and analysing multiple interference fringes to avoid fringe ambiguity. Tests were performed on both a textured sample (with features oriented normal to the direction of sliding) and a non-textured reference sample, while angular velocity, applied normal load and lubricant temperature were controlled in order to study the effect of varying lubrication regime (as typically occurs in service). Results showed that the presence of surface pockets consistently enhances fluid film thickness in the mixed lubrication regime by approximately 20 nm. Although this is only a modest increase, the effect on friction is pronounced (up to 41% under these conditions), due to the strong dependence of friction on film thickness in the mixed regime. Conversely, in the full film regime, texture caused a reduction in film thickness and hence increased friction force, compared with the non-textured reference. Both textured and non-textured friction values show nearly identical dependence on film thickness, (showing that, under these conditions, texture-induced friction reduction results entirely from the change in film thickness). These results are important in providing
Reddyhoff T, Dobre O, Le Rouzic J, et al., 2015, Friction induced vibration in windscreen wiper contacts, Journal of Vibration and Acoustics: Transactions of the ASME, Vol: 137, Pages: 1-7, ISSN: 1048-9002
This research is aimed at understanding the mechanisms that give rise to friction induced noise in automotive windscreen wipers, with a focus on frequencies between 500 and 3500 Hz. To study this phenomenon, experimental friction, sound, and high-speed video measurements are combined with finite element modeling of a rubber wiper/glass contact. In agreement with previous research, simultaneous sound and friction measurements showed that wiper noise in this frequency range results from the negative damping effect caused by the dependence of friction on speed in the mixed lubrication regime. Furthermore, during sliding, the friction induced noise recorded by the microphone occurred in one of two frequency ranges (close to 1000 Hz and between 2000 and 2500 Hz). These coincided closely with the eigen-frequencies of first two bending modes, predicted by finite element modeling. Experimental observations also showed the wiper to be oscillating backward and forward without any torsional motion and that the thickness of the glass had no effect on the emitted noise. These observations highlight how friction induced noise—although caused by conditions within contact—has characteristics that are determined by the structure of the excited component. A number of additional findings are made. Most importantly, both experiment and finite element modeling showed that the presence of water in contact with the wiper modulates the frequency and amplitude of the emitted noise by effectively adding mass to the vibrating system. While this is occurring, Faraday-like standing waves are observed in the water. In addition to this, friction induced vibration is shown only to occur for glass surfaces with intermediate surface energies, which is possibly due to high contact angles preventing water reaching the contact. Based on the understanding gained, a number of suggestions are made regarding means of reducing windscreen wiper noise.
Leong JY, Zhang J, Sinha SK, et al., 2015, Confining Liquids on Silicon Surfaces to Lubricate MEMS, Tribology Letters, Vol: 59, ISSN: 1573-2711
Liquid lubrication may provide a solution tothe problem of high friction and wear in micro-electromechanicalsystems. Although the effectiveness of thisapproach has been demonstrated in laboratory-based frictiontests, practical constraints prevent it from being appliedin commercial devices. The main problem is how toposition the lubricant on a silicon surface in order to limitspreading and evaporation. This paper describes twotechniques to address this issue. First, low concentrationsof additives are used to promote autophobic behaviour.Tests’ results show that certain concentrations of bothmultiply alkylated cyclopentane and amine additives areeffective in halting the spread of hexadecane on silicon,and, in the latter case, cause the hexadecane drop to subsequentlyretract. The second approach involves applying amicro-contact printing technique previously used on goldsurfaces. Here, silicon surfaces are coated with octadecyltrichlorosilanemono-layers that are then selectively removed,using oxygen plasma, to leave regions ofcontrasting surface energy. Results from spin tests showthat surfaces treated in this way can anchor 1 ll drops ofhexadecane and water when forces of up to 22 and 230 lN,respectively, are applied.
Ku ISY, Chong WWF, Reddyhoff T, et al., 2015, Frictional characteristics of molecular length ultra-thin boundary adsorbed films, Meccanica, Vol: 50, Pages: 1915-1922, ISSN: 1572-9648
The paper presents measurements of friction of any ultra-thin film entrained into the contact of a pair of very smooth specimen subjected to entrainment in a converging micro-wedge of a special-purpose micro-tribometer. An ultra-thin film is expected to form at the boundary solids through adsorption of boundary active molecules. Fluids with linear and branched molecules are used in the investigation. It is found that the frictional characteristics of these films can be adequately described through use of Eyring thermal activation energy and a potential energy barrier to sustain conjunctional sliding motion. The combined experimental measurement and the simple activation energy approach shows that the thin molecular adsorbed films act like hydro Langmuir–Blodgett layers, the formation and frictional characteristics of which are affected by the competing mechanisms of adsorption, forced molecular re-ordering and discrete-fashion drainage through the contact by the solvation effect. This process is a complex function of the contact sliding velocity as well as a defined Eyring activation density (packing density of the molecules within the conjunction). It is shown that the contribution of solvation to friction is in the form of energy expended to eject layers of lubricant out of the contact, which unlike the case of micro-scale hydrodynamic films, is not a function of the sliding velocity.
Medina S, Fowell MT, Vladescu S-C, et al., 2015, Transient effects in lubricated textured bearings, Proceedings of the Institution of Mechanical Engineers Part J - Journal of Engineering Tribology, Vol: 229, Pages: 523-537, ISSN: 1350-6501
Ma G, Wang L, Gao H, et al., 2015, The friction coefficient evolution of a TiN coated contact during sliding wear, Applied Surface Science, Vol: 345, Pages: 109-115, ISSN: 0169-4332
Liang H, Guo D, Reddyhoff T, et al., 2015, Influence of thermal effects on elastohydrodynamic (EHD) lubrication behavior at high speeds, SCIENCE CHINA-TECHNOLOGICAL SCIENCES, Vol: 58, Pages: 551-558, ISSN: 1674-7321
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Vladescu S-C, Olver AV, Pegg IG, et al., 2015, The effects of surface texture in reciprocating contacts - An experimental study, TRIBOLOGY INTERNATIONAL, Vol: 82, Pages: 28-42, ISSN: 0301-679X
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Putignano C, Le Rouzic J, Reddyhoff T, et al., 2014, A theoretical and experimental study of viscoelastic rolling contacts incorporating thermal effects, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY, Vol: 228, Pages: 1112-1121, ISSN: 1350-6501
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Le Rouzic J, Reddyhoff T, 2014, Spatially Resolved Triboemission Measurements, Tribology Letters, Vol: 55, Pages: 245-252, ISSN: 1573-2711
Hernandez Battez A, Viesca JL, Gonzalez R, et al., 2014, Effect of Shear Rate, Temperature, and Particle Concentration on the Rheological Properties of ZnO and ZrO<sub>2</sub> Nanofluids, TRIBOLOGY TRANSACTIONS, Vol: 57, Pages: 489-495, ISSN: 1040-2004
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Quinchia LA, Delgado MA, Reddyhoff T, et al., 2014, Tribological studies of potential vegetable oil-based lubricants containing environmentally friendly viscosity modifiers, TRIBOLOGY INTERNATIONAL, Vol: 69, Pages: 110-117, ISSN: 0301-679X
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Yang S, Reddyhoff T, Spikes H, 2013, Influence of Lubricant Properties on ARKL Temperature Rise and Transmission Efficiency, TRIBOLOGY TRANSACTIONS, Vol: 56, Pages: 1119-1136, ISSN: 1040-2004
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Moorhouse BS, Reddyhoff T, Ward-Close M, et al., 2013, Formation of wear resistant coatings on Ti-6Al-4V by calciothermic reduction, SURFACE & COATINGS TECHNOLOGY, Vol: 221, Pages: 214-221, ISSN: 0257-8972
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Le Rouzic J, Reddyhoff, Tom, 2013, Development of Infrared Microscopy for Measuring Asperity Contact Temperatures, Journal of Tribology, Vol: 135, Pages: 021504-021504, ISSN: 0742-4787
Leong JY, Reddyhoff T, Sinha SK, et al., 2013, Hydrodynamic friction reduction in a MAC-hexadecane lubricated MEMS contact, Tribology Letters, Vol: 49, Pages: 217-225, ISSN: 1023-8883
Recent research has shown that hydrodynamic lubrication is an effective means of reducing friction in high sliding micro-electromechanical systems (MEMS). At high speeds, however, such lubrication can lead to increased friction due to viscous drag. This article describes a series of hydrodynamic tests on a silicon MEMS contact lubricated with a blend of hexadecane and a multiplyalkylated cyclopentane (MAC). Results show that the presence of the MAC reduces hydrodynamic friction compared with neat hexadecane. Such behaviour is contrary to conventional hydrodynamic theory, since the viscosity of the MAC - a mixture of di and tri(2 octyldodecyl)cyclopentane - is significantly higher than that of neat hexadecane. This effect increases with MAC concentration up to an optimum value of 3 wt%, where the hydrodynamic friction coefficient at 15,000 rpm is reduced from 0.5 to 0.3. Above this concentration, friction begins to rise due to the overriding effect of increasing viscosity. The viscosity of the blended lubricant increased monotonically with MAC concentration, when measured using both a Stabinger and an ultrahigh shear viscometer. In addition to this, no reduction in friction was observed when a squalane-hexadecane blend of equal viscosity was tested. This suggests that some property of the MAC-hexadecane lubricant, other than its viscosity, is influencing hydrodynamic lubrication. A tentative explanation for this behaviour is that the MAC induces the liquid to slip, rather than shear, close to the silicon surfaces. This hypothesis is supported by the fact that the friction reducing ability of the MAC blend was inhibited by the inclusion of octade-cylamine - a substance known to form films on silicon surfaces. Furthermore, the MAC reduces friction in the mixed regime, in a manner suggesting that the formation of a viscous boundary layer. This unusual behaviour may have useful implications for reducing hydrodynamic friction in liquidlubricated MEMS devices. © Sprin
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