Bacterially induced degradation of aqueous solutions of poly(l-lysine)-graft-poly(ethylene glycol) and poly(l-lysine)-graft-dextran: consequences for their lubrication properties

Experimental data are presented comparing the degradation in the lubrication behaviour of aqueous solutions of the brush copolymers poly(l -lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) and poly(l -lysine)-graft-dextran (PLL-g-dex) when aged after exposure to bacterial contamination. While PLL-g-PEG solutions appear to be relatively unaffected by bacteria after a storage period of as much as 8 weeks, PLL-g-dex solutions exposed to bacteria during preparation lead to as much as a twofold increase in friction coefficient, when used as a lubricant in tribological tests, over an 8 week period when compared to reference data from freshly prepared and tested samples. Solutions prepared under sterile conditions and aged for up to 8 weeks do not appear to be degraded. Further experiments implementing the anti-bacterial agent sodium azide effectively prevented bacterial colonization and degradation in lubrication behaviour. Copyright © 2009 John Wiley & Sons, Ltd.     

The Influence of Molecular Architecture on the Macroscopic Lubrication Properties of the Brush-Like Co-polyelectrolyte Poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) Adsorbed on Oxide Surfaces

The co-polymer poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) has been investigated as a potential biomimetic boundary-lubrication additive for aqueous lubrication systems. In this work, the influence of the co-polymer's architecture on its tribological performance has been investigated. The architectural parameters investigated comprise side-chain (PEG) length, Lys/PEG grafting ratio and backbone chain (PLL) length. The tribological approaches applied in this work include ultra-thin-film interferometry, the mini-traction machine (MTM), and pin-on-disk tribometry. Both an increase in the molecular weight of the PEG side chains and a reduction in the grafting ratio result in an improvement in the lubricating properties of aqueous PLL-g-PEG solution at low speeds. MTM measurements show that an increase in the molecular weight of the PLL backbone results in an increase of the coefficient of friction.     

Boundary Lubrication of Oxide Surfaces by Poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) in Aqueous Media

In this work, we have explored the application of poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) as an additive to improve the lubricating properties of water for metal-oxide-based tribo-systems. The adsorption behavior of the polymer onto both silicon oxide and iron oxide has been characterized by optical waveguide lightmode spectroscopy (OWLS). Several tribological approaches, including ultra-thin-film interferometry, the mini traction machine (MTM), and pin-on-disk tribometry, have been employed to characterize the frictional properties of the oxide tribo-systems in various contact regimes. The polymer appears to form a protective layer on the tribological interface in aqueous buffer solution and improves both the load-carrying and boundary-layer-lubrication properties of water.     

Self-healing behavior of a polyelectrolyte-based lubricant additive for aqueous lubrication of oxide materials

We report on the self-healing behavior of a polyelectrolyte-based aqueous lubricant additive, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), during aqueous lubrication of an oxide-based tribosystem. Combined pin-on-disk tribometry and fluorescence microscopy experiments have shown that stable lubricating performance was enabled by means of rapid healing of the worn tribopair surface by polymers dissolved in the adjoining bulk lubricant. This rapid ‘self-healing’ of PLL-g-PEG is attributed to electrostatic interactions between the polycationic poly(l-lysine) (PLL) backbone of the polymer and negatively charged oxide surface. In contrast, a similar healing effect was not readily achievable in the case of methoxy-poly(ethylene glycol)-trimethylsilylether (Sil-PEG), a lubricant additive that is covalently bonded to the surface prior to tribological stress.     

Tribological performance of poly(sodium 4‐styrenesulphonate) as additive in water–glycol hydraulic fluid

The tribological behaviour of poly(sodium 4‐styrenesulphonate) (PSS) as additive in the base fluid of water–glycol hydraulic fluid was evaluated with four‐ball machine and Optimol SRV‐IV (Optimol Instruments, Munich, Germany) oscillating friction and wear tester, and its viscosity‐enhancing performance was also investigated. The results show that PSS exhibits excellent friction‐reducing and anti‐wear properties in the base fluid and can significantly improve the latter's welding load and viscosity. The worn surfaces were characterised by scanning electron microscope and X‐ray photoelectron spectroscopy. The analytical results of typical elements on the worn surfaces demonstrate that PSS molecules adsorb on the rubbing surface and form a stable chemically absorbed film through the interactions between the sulphonate anions and surface metallic atoms during the sliding process, which contributed to improve the tribological properties of the base fluid. Copyright © 2012 John Wiley & Sons, Ltd.     

Benzimidazolyl phosphates as anti‐wear additives in poly(ethylene glycol) for steel/steel contacts

Four novel benzimidazolyl phosphates (BPs) were synthesized and evaluated as anti‐wear additives in poly(ethylene glycol) for steel/steel contacts. The friction experiments were carried out on an Optimol SRV‐I oscillating reciprocating friction and wear tester (SRV) both at room temperature and high temperature. The worn surfaces of the steel discs were analysed by JSM‐5600LV scanning electron microscope and PHI‐5702 multifunctional X‐ray photoelectron spectrometer. It was indicated that poly(ethylene glycol) with 2 wt% BP additives had better friction‐reducing and anti‐wear properties than the commercial lubricant additive, tricresyl phosphate. Excellent tribological performance of BPs could be ascribed to the formation of high quality boundary films that consisted of the ordered adsorption films and tribo‐chemical reaction films. Copyright © 2013 John Wiley & Sons, Ltd.     

Scratch properties of poly(methyl methacrylate) surfaces: The time‐temperature dependence of friction and hardness

Viscoelastic‐viscoplastic behaviour is usually not taken into account in models describing the scratch properties of polymeric surfaces. In the case of a standard indentation test with stationary tip, the elastic‐plastic boundary and the boundary of the region being subjected to hydrostatic pressure beneath the tip are understood. Such well‐known models have been used in this study to understand the geometry of the groove left on the surface of a viscoelastic‐viscoplastic body by a moving diamond tip. A new apparatus was built that can control the velocity of the tip over the range 1 μm/s to 15 mm/s, at several different temperatures from −10 to +100°C. The material used was a commercial grade of cast poly(methyl methacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress‐ and temperature‐activated process. The values for the activation energy and volumes of the dynamic hardness and of the interfacial shear stress were in good agreement with the mechanical properties usually attributed to PMMA.     

Nanoscale Fabrication of the Ferroelectric Polymer Poly(vinylidene Fluoride with Trifluoroethylene) P(VDF‐TrFE) 75:25 Thin Films by Atomic Force Microscope Nanolithography

Thin films of an organic ferroelectric system, poly(vinylidene fluoride with trifluoroethylene) P(VDF‐TrFE, Kureha Corporation, Tokyo, Japan) 75:25 layers, have been deposited on highly ordered pyrolytic graphite and silicon dioxide by the horizontal Schaefer method of Langmuir–Blodgett techniques. It is possible to “shave” or mechanically displace small regions of the polymer film by using atomic force microscope nanolithography techniques such as nanoshaving, leaving swaths of the surface cut to a depth of 4 nm and 12 nm exposing the substrate. The results of fabricating stripes by nanoshaving two holes close to each other show a limit to the material “stripe” widths of an average of 153.29 nm and 177.67 nm that can be produced. Due to the lack of adhesion between the substrates and the polymer P(VDF‐TrFE) film, smaller “stripes” of P(VDF‐TrFE) cannot be produced, and it can be shown by the sequencing of nanoshaved regions that “stripes” of thin films can be removed. SCANNING 34: 404‐409, 2012. © 2012 Wiley Periodicals, Inc.