Engineering tribology

We have investigated the tribological properties of surfaces with adsorbed poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) sliding in aqueous glycerol solutions under different lubrication regimes. Glycerol is a polar, biocompatible liquid with a significantly higher viscosity than that of water. Macrotribological performance was investigated by means of pin-on-disk and mini-tractionmachine measurements in glycerol-PLL-g-PEG-aqueous buffer mixtures of varying compositions. Adsorption studies of PLL-g-PEG from these mixtures were conducted with the quartz-crystal-microbalance technique. The enhanced viscosity of the glycerol-containing lubricant reduces the coefficient of friction due to increased hydrodynamic forces, leading to a more effective separation of the sliding partners, while the presence of hydrated polymer brushes at the interface leads to an entropically driven repulsion, which also helps mitigate direct asperity-asperity contact between the solid surfaces under boundary-lubrication conditions. The combination of polymer layers on surfaces with aqueous phases of enhanced viscosity thus enables the friction to be reduced by several orders of magnitude, compared to the behavior of pure water, over a large range of sliding speeds. The individual contributions of the polymer and the aqueous glycerol solutions in reducing the friction have been studied across different lubrication regimes.

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“…The relative magnitude of the film thickness in comparison to the surface roughness is given by the k ratio [32].…”

Section: ''Rehealing'' Studies Of Pll-g-peg In Aqueousmentioning

confidence: 99%

Macrotribological Studies of Poly(L-lysine)-graft-Poly(ethylene glycol) in Aqueous Glycerol Mixtures

et al. 2009

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“…One of the key findings is that the lubricant film thickness does not obey EHL rules; i.e. positive speed and negligible load dependency 2014;Stachowiak and Batchelor;. It was concluded that film thickness predictions could not be made using simple Newtonian fluid rheology and steady state contact conditions.…”

Section: Introductionmentioning

confidence: 99%

The effect of transient conditions on synovial fluid protein aggregation lubrication

Myant

Cann

2014

Journal of the Mechanical Behavior of Biomedical Materials

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Little is known about the prevailing lubrication mechanisms in artificial articular joints and the way in which these mechanisms determine implant performance. The authors propose that interfacial film formation is determined by rheological changes local to the contact and is driven by aggregation of synovial fluid proteins within the contact inlet region. A direct relationship between contact film thickness and size of the protein aggregation within the inlet region has been observed.In this paper the latest experimental observations of the protein aggregation mechanism are presented for conditions which more closely mimic joint kinematics and loading. Lubricant films were measured for a series of bovine calf serum solutions for CoCrMo femoral component sliding against a glass disc. An optical interferometric apparatus was employed to study the effects of transient motion on lubricant film formation. Central film thickness was measured as a function of time for a series of transient entrainment conditions; start-up motion, steady-state and non-steadystate uni-directional sliding, and bi-directional sliding. The size of the inlet aggregations was found to be dependent upon the type of transient condition. Thick protective protein films were observed to build up within the main contact region for all uni-directional tests. In contrast the inlet aggregation was not observed for bi-directional tests. Contact film thickness and wear was found to be directly proportional to the presence of the inlet protein phase. The inlet phase and contact films were found to be fragile when disrupted by surface scratches or subjected to reversal of the sliding direction.

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“…In this case the friction may be predicted in terms of the traction forces acting on the film [11], neglecting the surface roughness effect on friction. For moderate loads hydrodynamic friction is independent of the normal load, but it is a function of matrix viscosity, film thickness and pulling rate according to…”

Section: Introductionmentioning

confidence: 99%

“…The coexistence of two lubrication modes, hydrodynamic and boundary lubrication, is referred to as the regime of mixed lubrication. The asperity contact area is determined from geometric features of the surface and its ability to deform during applied normal force [11,12]. In composite applications it is expected that surface roughness in combination with matrix distribution is important to the interply friction behaviour.…”

Section: Introductionmentioning

confidence: 99%

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On the interply friction of different generations of carbon/epoxy prepreg systems

Larberg

Åkermo

2011

Composites Part A: Applied Science and Manufacturing

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Using pre-stacked material that is formed as a first step in the manufacturing process offers reduced process cycle time for production of complex structural components. The forming is achieved by forcing layers to deform by e.g. intraply deformation and interply slippage, where the latter is the scope of this study. The prepreg-prepreg friction is experimentally determined for four unidirectional carbon/epoxy prepreg systems. The materials differ considering volume fraction of fibres, fibre stiffness and phase of thermoplastic toughener (solved or particles). The study shows large individual differences between the tested materials, where the material systems with particle tougheners seem to obey a boundary lubrication friction, while the other materials show hydrodynamically dominated friction. A large difference between the high and low friction materials, almost a factor of 10, correlates to trends seen in the herein performed surface roughness measurements. Vacuum as well as autoclave consolidated materials are tested.

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Engineering tribology

Cited by 77 publications

References 0 publications

Macrotribological Studies of Poly(L-lysine)-graft-Poly(ethylene glycol) in Aqueous Glycerol Mixtures

Macrotribological Studies of Poly(L-lysine)-graft-Poly(ethylene glycol) in Aqueous Glycerol Mixtures

The effect of transient conditions on synovial fluid protein aggregation lubrication

On the interply friction of different generations of carbon/epoxy prepreg systems

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