Journal: Tribology Letters

Abbreviation

Tribol Lett

Publisher

Springer

Journal Volumes

ISSN

1023-8883
1573-2711

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Publications 1 - 10 of 43
  • Substituent Effect on the Reactivity of Alkylated Triphenyl Phosphorothionates in Oil Solution in the Presence of Iron Particles
    Item type: Journal Article
    Mangolini, Filippo; Rossi, Antonella; Spencer, Nicholas D. (2010)
    Tribology Letters
  • A combinatorial approach to elucidating tribochemical mechanisms
    Item type: Journal Article
    Eglin, Michael; Rossi, Antonella; Spencer, Nicholas D. (2003)
    Tribology Letters
  • Aqueous lubrication of SiC and Si3N4 ceramics aided by a brush-like Copolymer additive, poly(L -lysine)- graft -poly(ethylene glycol)
    Item type: Journal Article
    Hartung, Whitney; Rossi, Antonella; Lee, Seunghwan; et al. (2009)
    Tribology Letters
  • Ultrathin, Oil-Compatible, Lubricious Polymer Coatings
    Item type: Journal Article
    Bielecki, Robert M.; Doll, Patricia; Spencer, Nicholas D. (2013)
    Tribology Letters
  • In Situ Attenuated Total Reflection (ATR/FT-IR) Tribometry
    Item type: Journal Article
    Mangolini, Filippo; Rossi, Antonella; Spencer, Nicholas D. (2012)
    Tribology Letters
  • Self-healing behavior of a polyelectrolyte-based lubricant additive for aqueous lubrication of oxide materials
    Item type: Journal Article
    Lee, S.; Müller, M.; Heeb, R.; et al. (2006)
    Tribology Letters
  • Molecular Mechanisms of Self-mated Hydrogel Friction
    Item type: Journal Article
    Mees, Jan; Simič, Rok; O’Connor, Thomas C.; et al. (2023)
    Tribology Letters
    Hydrogel-like structures are responsible for the low friction experienced by our joints when we walk or by our eyelids when we blink. At low loads, hydrogel contacts show extremely low friction that rises with velocity beyond a threshold speed. Here we combine mesoscopic simulations and experiments to test the polymer-relaxation hypothesis for this velocity dependence, where a velocity-dependent regime emerges when the perturbation of interfacial polymer chains occurs faster than their relaxation at high velocity. Our simulations quantitatively match the experimental findings, with a friction coefficient that rises with velocity to some power of order unity in the velocity-dependent regime. We show that the velocity-dependent regime is characterized by reorientation and stretching of polymer chains in the direction of shear, leading to an entropic stress that can be quantitatively related to the shear response. The detailed exponent of the power law in the velocity-dependent regime depends on how chains interact: We observe a power close to 1/2 for chains that can stretch, while pure reorientation leads to a power of unity. These results show that the friction of hydrogel interfaces can be engineered by tuning the morphology of near-surface chains.
  • Towards a Polymer-Brush-Based Friction Modifier for Oil
    Item type: Journal Article
    Gmür, Tobias A.; Mandal, Joydeb; Cayer-Barrioz, Juliette; et al. (2021)
    Tribology Letters
    To meet the need for oil-compatible friction modifier additives that can significantly reduce energy consumption in the boundary-lubrication regime, a macromolecular design approach has been taken. The aim was to produce a lubricious polymer film on the sliding surfaces. A series of readily functionalizable block copolymers carrying an oleophilic poly(dodecyl methacrylate) block and a functionalizable poly(pentafluorophenyl methacrylate) block of various lengths was synthesized by means of reversible addition-fragmentation chain-transfer (RAFT) polymerization. The poly(pentafluorophenyl methacrylate) block was used to attach surface-active nitrocatechol anchoring groups to the polymer. The friction-reduction properties of these polymers were assessed with 0.5 wt% solutions in hexadecane by means of rolling-sliding macroscopic tribological tests. Block copolymers with roughly equal block lengths and moderate molecular weights were significantly more effective at friction reduction than all other architectures investigated. They also displayed lower friction coefficients than glycerol monooleate-a commercially used additive. The film-formation ability of these polymers was examined using a quartz-crystal microbalance with dissipation (QCM-D), by monitoring their adsorption onto an iron oxide-coated QCM crystal. The polymer with highest lubrication efficiency formed a thin film of similar to 17 nm thickness on the crystal, indicating the formation of a polymer brush. Interferometric rolling-sliding experiments with the same polymer showed a separating film thickness of similar to 20 nm, which is consistent with the QCM-D value, bearing in mind the compression of the adsorbed layers on the two sliding surfaces during tribological testing.
  • Anomalous Wear Behavior of UHMWPE During Sliding Against CoCrMo Under Varying Cross-Shear and Contact Pressure
    Item type: Journal Article
    Dreyer, Michael J.; Taylor, William R.; Wasmer, Kilian; et al. (2022)
    Tribology Letters
    Wear of ultra-high-molecular weight polyethylene (UHMWPE) in joint implant applications has been shown to increase with cross-shear (CS, i.e., multidirectional sliding) but decrease with higher contact pressure (CP). Moreover, structural changes, resulting in protrusions, are known to occur to the surface of the pin following multidirectional sliding. However, these phenomena are not yet fully understood. In this study, we simultaneously varied CP and CS to derive an empirical formula for the wear factor as a function of these parameters. The wear factor increased when going from unidirectional sliding to multidirectional sliding but decreased with increasing CP, as has been previously observed. Following these tests, the protrusions on the pin surface were chemically and mechanically characterized to gain insights into both their origin and influence on wear behavior. Micro-FT-IR confirmed that the structures consist of polyethylene, rather than adsorbed, denatured proteins. It also allowed the crystallinity of both the protrusions and unaffected UHMWPE to be estimated, showing a strong positive correlation with the hardness of these different areas on the surface. Time-of-flight secondary-ion mass spectrometry was used to probe the chemistry of the surface and near-surface region and indicated the presence of contamination from the test fluid within the structure. This suggests that the protrusions are formed by the folding of UHMWPE following plastic deformation. It is also suggested that the higher hardness of the protrusions affords some protection of the surface, leading to the observed anomalous behavior, whereby wear increases with decreasing CP.
  • Mimicking the Mouth in a Tribometer: Immobilizing a Lubricious Salivary Mucin for Frictional Measurements of Astringency Effects in Beverages and Foodstuffs
    Item type: Journal Article
    Roye, Ashley; Yap, Kian Kun; Weston, Abby; et al. (2026)
    Tribology Letters
    Astringency is a property of food and beverages that results largely from a friction-enhancing effect in the mouth. It can be conveniently assessed by tribological measurements, which have typically been carried out by investigating the effect of the astringent on the lubricating properties of whole-mouth saliva (WMS). Saliva is notoriously variable as a reagent, however, differing in its properties from person to person, day to day, and changing its behavior rapidly after removal from the mouth. We describe a far more convenient, reproducible, and potentially useful alternative to the use of WMS for ex vivo determination of the friction-enhancing effects of an astringent substance. Key to this development is the use of a nitrene-generating adhesion promoter to immobilize a crucial lubricating mucin, MUC5B, onto the tribopair-in this case silicone rubber (PDMS) and glass. Upon sliding in saline solution, this mucin-modified tribopair exhibits friction coefficients in the range of 0.002-0.006. Addition of 1 wt% potassium alum solution (a known astringent) leads to an order-of-magnitude increase in friction coefficient, while addition of samples of greater relevance to the food and beverage industry (grapeskin extract, red wine) shows comparable effects. Interestingly, the astringents' effect on the MUC5B-modified surfaces appears to be essentially reversible upon washing with saline solution and continued sliding, suggesting that the effects of astringents in the mouth are not necessarily associated with removal of the MUC5B from the oral mucosa.
Publications 1 - 10 of 43