Publications
60 results found
Yang S, Wong J, Cai M, et al., 2018, Tribological Properties of In-situ Ionic Liquid Additives for Mixed and Hydrodynamic Lubrication, Mocaxue Xuebao/Tribology, Vol: 38, Pages: 342-348, ISSN: 1004-0595
© 2018, Science Press. All right reserved. This work focused on studying the tribological performance of IL additives in the mixed and hydradynamic lubrication regimes. Polyethylene glycol (PEG-400) was used as the base fluid, ILs were synthesized in situ by dissolving lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in PEG. Mini Traction Machine was used to measure the friction coefficients with entrainment speeds at room temperature, 60 ℃ and 80 ℃ and at various slide-roll ratios for confirming the effect of IL additives on the tribological properties, and the rheological behavior of PEG was also investigated. This work would provide a new research method for further study of the lubrication mechanism of ionic liquids, which is of great significance for guiding the design of new ionic liquid lubricating materials.
Jean-Fulcrand A, Masen M, Bremner T, et al., 2017, High Temperature Tribological Properties of Polybenzimidazole (PBI), Polymer, Vol: 128, Pages: 159-168, ISSN: 0032-3861
Polybenzimidazole (PBI) is a high performance polymer that can potentially replace metal components in some high temperature conditions where lubrication is challenging or impossible. Yet most characterisations so far have been conducted at relatively low temperatures. In this work, the tribological properties of PBI were examined with a steel ball-PBI disc contact at 280 °C under high load and high sliding speed conditions. The dry friction coefficient is relatively low and decreases modestly with increasing applied load. Surface analysis shows that PBI transfer layers are responsible for the low friction observed. In-situ contact temperature measurements were performed to provide for the first time direct links between the morphology and distribution of the transfer layer, and the temperature distribution in the contact. The results show that high pressure and high temperature in heavily loaded contacts promote the removal and the subsequent regeneration of a transfer layer, resulting in a very thin transfer layer on the steel counterface. FeOOH is formed in the contact at high loads, instead of Fe2O3. This may affect the adhesion between PBI and the counterface and thus influence the transfer layer formation process. To control PBI wear, contact temperature management will be crucial.
Campen S, di Mare L, Smith B, et al., 2017, Determining the kinetics of asphaltene adsorption from toluene; a new reaction-diffusion model, Energy and Fuels, Vol: 31, Pages: 9101-9116, ISSN: 0887-0624
Fouling by asphaltene, which constitutes the densest, most polar fraction of crude oil, poses a serious problem for the oil production industry. In order to obtain a fundamental understanding of asphaltene deposition, it is necessary to determine both the thermodynamics and kinetics that govern this process. In recent years, there have been numerous studies of the kinetics of asphaltene adsorption; however, a consensus on the model that best describes asphaltene adsorption remains elusive. In this work the adsorption of asphaltene from solution in toluene onto a gold surface is investigated using a quartz crystal microbalance inside a flow cell. The kinetics of adsorption depends on the state of the asphaltene in solution, and the adsorption behavior is altered with long-time aging of asphaltene solutions. A model is developed that links the kinetics of asphaltene adsorption to the bulk solution properties in terms of coexisting monomer and multimer states. A large portion of deposited asphaltene is effectively irreversibly bound and not easily removed by rinsing with toluene. The model suggests that asphaltene–asphaltene interactions play an important role in the formation of irreversibly bound deposits, which could lead to fouling problems.
Guo YY, di Mare L, Li RKY, et al., 2017, Structure of Amphiphilic Terpolymer Raspberry Vesicles, Polymers, Vol: 9, ISSN: 2073-4360
Terpolymer raspberry vesicles contain domains of different chemical affinities. They are potential candidates as multi-compartment cargo carriers. Their efficacy depends on their stability and load capacity. Using a model star terpolymer system in an aqueous solution, a dissipative particle dynamic (DPD) simulation is employed to investigate how equilibrium aggregate structures are affected by polymer concentration and pairwise interaction energy in a solution. It is shown that a critical mass of polymer is necessary for vesicle formation. The free energy of the equilibrium aggregates are calculated and the results show that the transition from micelles to vesicles is governed by the interactions between the longest solvophobic block and the solvent. In addition, the ability of vesicles to encapsulate solvent is assessed. It is found that reducing the interaction energy favours solvent encapsulation, although solvent molecules can permeate through the vesicle’s shell when repulsive interactions among monomers are low. Thus, one can optimize the loading capacity and the release rate of the vesicles by turning pairwise interaction energies of the polymer and the solvent. The ability to predict and control these aspects of the vesicles is an essential step towards designing vesicles for specific purposes.
Dench J, Morgan N, Wong J, 2016, Quantitative viscosity mapping using fluorescence lifetime measurements, Tribology Letters, Vol: 65, ISSN: 1573-2711
Lubricant viscosity is a key driver in both the tribological performance and energy efficiency of a lubricated contact. Elastohydrodynamic (EHD) lubrication produces very high pressures and shear rates, conditions hard to replicate using conventional rheometry. In situ rheological measurements within a typical contact are therefore important to investigate how a fluid behaves under such conditions. Molecular rotors provide such an opportunity to extract the local viscosity of a fluid under EHD lubrication. The validity of such an application is shown by comparing local viscosity measurements obtained using molecular rotors and fluorescence lifetime measurements, in a model EHD lubricant, with reference measurements using conventional rheometry techniques. The appropriateness of standard methods used in tribology for high-pressure rheometry (combining friction and film thickness measurements) has been verified when the flow of EHD lubricant is homogeneous and linear. A simple procedure for calibrating the fluorescence lifetime of molecular rotors at elevated pressure for viscosity measurements is proposed.
Laux K, Jean-Fulcrand A, SUE HJ, et al., 2016, The influence of surface properties on sliding contact temperatureand friction for Polyetheretherketone (PEEK), Polymer, Vol: 103, Pages: 397-404, ISSN: 0032-3861
Polyetheretherketone (PEEK) polymers are increasingly used intribological applications. An important aspect of PEEK tribology is thesurface temperature reached during sliding. However, most knowledge offrictional heating in PEEK is based on post-hoc analysis of debris andwear surfaces. In this study, infrared thermography was used to observethe full field temperature map of PEEK during ball-on-disc sliding.Although the measured temperatures were below any thermal transition, theresults matched closely to those predicted by flash temperature models.Additionally, friction studies were performed with steel and sapphirecounterfaces. It was observed that PEEK debris was readily deposited tosteel but not on sapphire. The friction studies also indicated a greateradhesive friction response for PEEK against steel compared to sapphire.The transfer of PEEK material to the steel surface may elevate thetemperature at the sliding interface. Analysis of films formed on steelsuggests that the transferred PEEK was oriented in the direction ofsliding. The deposition of debris and formation of oriented filmsresembled a high temperature drawing process, which was likely to be dueto localized frictional heating. The results of this study illustrate theimportant role transfer films play in determining both the friction andtemperature response of the PEEK wear interface.
Jean-Fulcrand A, Wong J, Masen M, et al., 2016, Tribological properties of PBI and PEEK polymers on steel, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Tysoe W, Spencer N, 2016, Looking at lube in a new light, Publisher: Society of Tribologists and Lubrication Engineers
Galmiche B, Ponjavic A, Wong J, 2016, Flow measurements of a polyphenyl ether oil in an elastohydrodynamic contact, Journal of Physics: Condensed Matter, Vol: 28, ISSN: 0953-8984
A novel methodology, based on the use of phosphorescence imaging, is applied to determine the local through-thickness velocity profile of lubricant in an elastohydrodynamic (EHD) contact. The technique has spatial and temporal resolutions of 40 µm and 340 µs respectively and thus allows lubricant rheology to be investigated at conditions close to service conditions. The capability of the newly-developed method is verified by examining the flow of 5P4E polyphenyl ether, a lubricant base fluid used in very high temperature applications and well-known for its high viscosity-pressure coefficient. Experimental results highlight the effect of the contact pressure on the velocity profile of this fluid in lubricated contacts. At low pressures, the velocity profile of 5P4E is close to linear, characteristic of Couette flow. As the local pressure increases, its velocity profile progressively deviates from a Couette profile and shear banding is evident at high pressure.
Ponjavic A, Dench J, Morgan N, et al., 2015, In situ viscosity measurement of confined liquids, RSC Advances: an international journal to further the chemical sciences, Vol: 5, Pages: 99585-99593, ISSN: 2046-2069
The viscosity of liquids governs crucial physical and engineering phenomena, ranging from diffusion and transport processes of nutrients and chemicals, to the generation of friction and the physics of damping. Engineering fluids frequently experience local conditions that change their bulk rheological properties. While viscosity data can easily be acquired using conventional rheometers, the results are not always applicable to fluids under engineering conditions. This is particularly the case for fluids being sheared at high pressure under severe confinement, which experience very high shear stresses and often show extensive shear thinning. There is a lack of suitable methods for measuring fluid viscosity under such conditions. This work describes a novel in situ viscosity measurement technique to fill this gap. It involves the quantification of the fluorescence lifetime of a fluorescent dye that is sensitive to viscosity. The capability of the developed technique is verified by taking measurements in submicron thick films of two model fluids confined in a ball on flat contact. Viscosity measurements were successfully performed at pressures up to 1.2 GPa and shear rates up to 105 s−1. Spatial heterogeneity in viscosity caused by variations in pressure within the thin fluid film could be observed using the technique. It was also possible to detect differences in the rheological responses of a Newtonian and a non-Newtonian fluid. These first in situ high pressure, high shear viscosity measurements demonstrate the versatility of the proposed technique in providing information on the viscosity in conditions where contemporary techniques are insufficient. More importantly it highlights the complexity of the rheology of engineering fluids and provides a means of verifying existing theories by performing in situ measurements. Information on local viscosity is crucial for understanding the physics of confined fluids and to facilitate improvements in engineering techno
Parkes M, Myant C, Cann PM, et al., 2015, Synovial fluid lubrication: The effect of protein interactions on adsorbed and lubricating films, Biotribology, Vol: 1-2, Pages: 51-60, ISSN: 2352-5738
© 2015 Elsevier Ltd. All rights reserved. Synovial fluid lubrication is dependent on protective protein films that form between joint surfaces. Under static conditions surface film formation occurs through adsorption, while under dynamic conditions protein aggregation under shear and load becomes the dominant mechanism. This work examines how the protein content of six model synovial fluids affects film formation under static and rolling conditions and if the changes in properties can be correlated. With an increase in the statically adsorbed mass and the rate of adsorption the film thickness under rolling increased. These increases did not correlate with the total protein content of the fluid, but were dependent on the type of protein. An increase in pH reduced the adsorbed mass, rate of adsorption and film thickness, but was of secondary importance to the type of protein. The rolling film thickness was also correlated with the viscoelastic properties of the films formed under static conditions. In this case thinner rolling films corresponded to the more hydrated, viscoelastic adsorbed films. The strong correlations found between the properties of the adsorbed films and those formed under rolling indicate that the same protein-protein and protein-surface interactions may govern both mechanisms of film formation despite the differences in the film structures.
Wong JSP, Hu M, Shi D, et al., 2014, In-situ Monitoring on Dynamics of Solute Transport in Polymer Films, Polymer, Vol: 58, Pages: 67-75, ISSN: 0032-3861
A new and non-invasive technique based on confocal laser scanning microscopy (CLSM) that allows the visualization of penetrant diffusion in-situ has been developed and was applied to quantify local solute dynamics in polymeric films. The effectiveness of the proposed technique was demonstrated using a model penetrant, rhodamine-6G (Rh-6G), and a system of polyvinyl alcohol (PVA) films with different degree of cross-linking, and different content of montmorillonite (MMT) clay. The penetrant's transport across PVA films were monitored by measuring the time evolutions of through thickness fluorescence intensity profiles. These profiles were then converted to concentration profiles, which allow local diffusion coefficients of the model solute (i.e. Rh-6G) to be determined. The developed methodology was applied to both single layer and bilayers films and local diffusion heterogeneity was detected. Hence the technique developed can be applied to multi-layer films, and can be beneficial to film developments for packaging and filtration technology.
Liu X, Spikes H, Wong JSS, 2014, In-situ pH responsive fluorescent probing of localized iron corrosion, Corrosion Science, ISSN: 0010-938X
Parkes M, Myant C, Cann PM, et al., 2014, The effect of buffer solution choice on protein adsorption and lubrication, Tribology International, Vol: 72, Pages: 108-117, ISSN: 0301-679X
Ponjavic A, di Mare L, Wong J, 2014, Effect of pressure on the flow behavior of polybutene, Journal of Polymer Science Part B: Polymer Physics, Vol: 52, Pages: 708-715, ISSN: 0887-6266
The rheology of submicron thick polymer melt is examined under high normal pressure conditions by a recently developed photobleached‐fluorescence imaging velocimetry technique. In particular, the validity and limitation of Reynold equation solution, which suggests a linear through‐thickness velocity profile, is investigated. Polybutene (PB) is sheared between two surfaces in a point contact. The results presented in this work suggest the existence of a critical pressure below which the through‐thickness velocity profile is close to linear. At higher pressures however, the profile assumes a sigmoidal shape resembling partial plug flow. The departure of the sigmoidal profile from the linear profile increases with pressure, which is indicative of a second‐order phase/glass transition. The nature of the transition is confirmed independently by examining the pressure‐dependent dynamics of PB squeeze films. The critical pressure for flow profile transition varies with molecular weight, which is consistent with the pressure‐induced glass transition of polymer melt.
Wong JSS, Ponjavic A, 2013, Through-thickness velocity profile of sheared sub-micron thick polymer melt
The through-thickness velocity profile of a sub-micron thick polymer melt, under - elastohydrodynamic (EHL) conditions, has been recently obtained for the first time by the authors using photobleached imaging technique. In this work, the developed technique is applied to investigate the effect of shear rate on the evolution of velocity profile in polybutene (PB). The velocity profile of PB in an EHL contact severely deviates from the common linear assumption and exhibits shear localization. Depending on the average shear rate experienced by the polymer melt, interfacial slips and localized shear banding were observed.
Ponjavic A, Wong JSS, 2013, The effect of boundary slip on elastohydrodynamic lubrication, RSC Advances, Vol: 4, Pages: 20821-20829, ISSN: 2046-2069
Ponjavic A, Chennaoui M, Wong JSS, 2013, Through-Thickness Velocity Profile Measurements in an Elastohydrodynamic Contact, Tribology Letters
The through-thickness flow profile of a lubricant within an elastohydrodynamic contact is challenging to obtain due to its small thickness. Yet, this information is crucial to the accurate friction estimation of the tribological system. In this work, a novel fluorescence based technique has been developed to extract such information in situ. The local through-thickness flow profiles map within a tribological contact is obtained for the first time. The profiles obtained are position depends with slip boundary condition observed in high normal stress locations.
Wong J, Ponjavic A, 2013, Flow-profile mapping in elastohydrodynamic lubrication region
Chennaoui M, Wong JSS, 2012, Corrosion of Aluminum in Oil-Based Nanoemulsion
While metal components immersed in oil-based lubricants suffer from corrosion, very few studies investigate such phenomenon. As water-in-oil nanoemulsions can be formed intentionally and accidently in oil lubricants, they were used as model systems in this corrosion study to investigate the effect of surface topography on corrosion of Aluminium. The initiation sites of corrosion were identified using fluorescence imaging with a resolution of 1 micrometer. It shows for the first time metal corrodes in oil-based nanoemulsion. It was found that corrosion preferentially occurred at regions with surface irregularity. The corrosion mechanisms are discussed using percolation theory and charge transfer in surfactant networks of semi-dilute micelle solutions.
Wong JSS, Hong L, Bae SC, et al., 2011, Polymer Surface Diffusion in the Dilute Limit, Macromolecules, Vol: 44
Wong JSS, Hong L, Bae SC, et al., 2010, Fluorescence Recovery after Photobleaching Measurements of Polymers in a Surface Forces Apparatus, Journal of Polymer Science. Part B, Polymer Physics, Vol: 48
Bae SC, Wong JSS, Kim M, et al., 2008, Using light to study boundary lubrication: spectroscopic study of confined fluids, Philosophical Transactions of the Royal Society A. Mathematical, Physical and Engineering Sciences, Vol: 366
Wong JSS, Granick S, 2007, Open questions about polymer friction, Journal of Polymer Science. Part B, Polymer Physics, Vol: 45
Wong JS, Bae SC, Anthony S, et al., 2006, Wong et al. Reply, Physical Review Letters, Vol: 96, ISSN: 0031-9007
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Granick S, Zhu Y, Lin Z, et al., 2006, Reply to comment on reassessment of solidification in fluids confined between mica sheets, Langmuir, Vol: 22, Pages: 2399-2401, ISSN: 0743-7463
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Wong J, Sue HJ, Zeng KY, et al., 2004, Surface damage of polymers in nanoscale, Pages: 1934-1937
Surface damage of polymers in the nanometer-range is examined and results correlated with material characteristics and surface roughness of epoxies. Under a constant loading and constant scratch rate testing condition, surface roughness plays little or no role in surface damage formed during the course of this study. Material characteristics influence the damage occurred in terms of variations in elastic recovery, damage pattern and damage mechanism. The variations in scratch head geometry, which, in turn, lead to the variations in magnitude of stress and stress field distribution, give rise to various scratch features on the polymer.
Mai YW, Wong JSS, Li RKY, et al., 2004, On the tearing toughness and permeability modelling of polymer nanocomposites, Pages: 1785-1789
This paper presents preliminary studies on two aspects of nylon-based nanoclay composite films: their out-of-plane tearing fracture resistance and moisture diffusion characteristics. Attempts to analyze the out-of-plane tearing fracture based on the essential work of fracture analysis will be presented. Also, theoretical modelling of the permeability of these polymer nanocomposites is also presented which takes into account the degree of exfoliation, orientation, aspect ratio and volume fraction of the nanoclay sheets; crystallinity of polymer matrix; and the affinity of polymer and clay with the diffusing species. Comparisons with published permeability data are given.
Wong JSS, Sue HJ, Zeng KY, et al., 2004, Scratch damage of polymers in nanoscale, Acta Materialia, Vol: 52, Pages: 431-443, ISSN: 1359-6454
Recent advances in nanoscience and nanotechnology have led to the development of miniaturized devices and components based on polymeric materials. These polymeric components and devices are subject to surface damage in the nanoscale range. Since the surface properties of polymers may be different from those of the bulk, techniques that focus on nanoscale surface damage have been applied to correlate surface damage with material characteristics and surface roughness of epoxies, polycarbonate, and polymethylmethacrylate. Under a constant loading and constant scratch rate testing condition, the results suggest that surface damage encountered is mainly material specific. Surface roughness plays little or no role in surface damage formed during the course of this study. Material characteristics influence the damage occurred when varying the penetration depth. Such variations can be assessed in terms of elastic recovery, damage pattern and damage mechanism. The variations in scratch head geometry, which, in turn, lead to the variations in magnitude of stress and stress field distribution, give rise to various scratch features on the polymer. © 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Wong JSS, Ferrer-Balas D, Li RKY, et al., 2003, On tearing of ductile polymer films using the essential work of fracture (EWF) method, Acta Materialia, Vol: 51, Pages: 4929-4938, ISSN: 1359-6454
The essential work of fracture (EWF) technique has been well established and accepted for the fracture characterization of ductile polymer films under in-plane (mode I) loading. In the present study, the technique has been further developed for the characterization of out-of-plane (mode III) tearing fracture of some ductile polymer films including PETG (polyethylene-terephthalate-glycol), PP homopolymer (H0) and a PP copolymer (C1). A two-zone model was proposed to describe the deformation and fracture behaviour of the tearing ligament. In the first zone, which is called zone A and is adjoining the initial crack-tip, the outer plastic zone height increases with the torn ligament length. At the end of zone A, the height of the plastic zone has saturated, and the deformation has entered zone B. The height of the outer plastic zone remains constant with further increase of torn ligament length. The zone B model is applicable to films with a large stabilized plastic zone (such as H0 and C1). It is observed that the tearing specific essential fracture work as measured from the zone A and zone B models are similar confirming the EWF concept can be applied to the mode III out-of-plane tearing of polymer films. © 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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