The Influence of Anchoring-Group Structure on the Lubricating Properties of Brush-Forming Graft Copolymers in an Aqueous Medium |
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Authors: | Whitney Hartung Tanja Drobek Seunghwan Lee Stefan Zürcher Nicholas D Spencer |
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Affiliation: | (1) Department of Materials, Laboratory for Surface Science and Technology, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland |
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Abstract: | We have compared the lubricating properties of two different PEG-grafted, polycationic, brush-forming copolymers to gain a
deeper understanding of the role of the polyionic backbone in the lubricating behavior of such materials, when used as additives
in aqueous lubricant systems. Previously, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) has been shown to adsorb onto oxide surfaces from aqueous solution and substantially lower frictional forces. Poly(allylamine)-graft-poly(ethylene glycol) (PAAm-g-PEG), which also has a polycationic backbone, has been synthesized in several different architectures, and its performance
investigated via adsorption tests, rolling- and sliding-contact tribometry, and the surface forces apparatus. These tests
show a clear reduction of friction forces with PAAm-g-PEG compared to water alone. However, when compared with PLL-g-PEG, while PAAm-g-PEG copolymers did not adsorb to the same extent or exhibit as high a lubricity in sliding geometry, they showed a similar
lubricating effect under rolling conditions. The difference in the chemical structure of the backbones, especially the flexibility
of the anchoring groups, appears to significantly influence both the extent and kinetics of polymer adsorption, which in turn
influences lubrication behavior.
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Keywords: | Poly(allylamine)-g-poly(ethylene glycol) (PAAm-g-PEG) l-lysine)-g-poly(ethylene glycol) (PLL-g-PEG)" target="_blank">Poly(l-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) Aqueous lubrication Polymer architecture Polymer brush Boundary lubrication Anchoring groups |
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