End-grafted Sugar Chains as Aqueous Lubricant Additives: Synthesis and Macrotribological Tests of Poly(l-lysine)-graft-Dextran (PLL-g-dex) Copolymers

Abstract

Comb-like graft copolymers with carbohydrate side chains have been developed as aqueous lubricant additives for oxide-based tribosystems, in an attempt to mimic biological lubrication systems, whose surfaces are known to be covered with sugar-rich layers. As adopted in the previous studies of the graft copolymer poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), which showed both excellent lubricating and antifouling properties, a similar approach was chosen to graft dextran chains onto the same backbone, thus generating PLL-g-dex. PLL-g-dex copolymers readily adsorb from aqueous solution onto negatively charged oxide surfaces. Tribological characterization at the macroscopic scale, either under pure sliding conditions or a mixed sliding/rolling contact regime, shows that PLL-g-dex is very effective for the lubrication of oxide-based tribosystems. The relative lubricating capabilities of PLL-g-dex copolymers compared with PLL-g-PEG copolymers were observed to be highly dependent on the molecular structure of the copolymers (in particular, sidechain density along the backbone) and the measurement conditions (in particular, time between tribocontacts); the PLL-g-dex copolymers with a low degree of grafted side chains (B20% grafting of available protonated primary amine groups along the backbone) showed better lubricating performance than their PLL-g-PEG counterparts at high tribocontact frequency (Cca. 0.32 Hz).

Mesh Size Control of Polymer Fluctuation Lubrication in Gemini Hydrogels

“…Gemini hydrogel friction behavior both resembles and differs from the lubrication of self-mated solvated polymer brushes [48][49][50]15]. Previous studies of polymer brushes measured in a surface force apparatus (SFM) have shown that at low speeds (~ 450 nm/s) these materials achieved extremely low friction coefficients (µ < 0.001) by polymer chain fluctuations [51].…”

Sugars Communicate through Water: Oriented Glycans Induce Water Structuring

“…Some experiments were performed in KNO 3 solutions at concentrations ranging from 1 mM to 100 mM to determine the influence of electrostatic double-layer forces. PLL(12kDa)-g(3.5)-dextran (5 kDa; see elsewhere (21,22) for details regarding synthesis and characterization) was adsorbed onto two mica surfaces by ex situ adsorption from the buffered polymer solution (0.25 mg/mL PLL-g-dextran) for 30 min at room temperature. The grafting density achieved was 0.3 nm À2 .…”

Load-Induced Transitions in the Lubricity of Adsorbed Poly(l-lysine)-g-dextran as a Function of Polysaccharide Chain Density

“…3,4,6À8 Recently, the lubrication properties of poly(L-lysine)-graft-dextran (PLL-g-dex) with a variety of grafting ratios and dextran molecular weights under aqueous conditions were also studied both on the macroand the nanoscale. 9,10 It was shown that PLL-g-dex lubricates metal oxide surfaces very efficiently, and readily forms highdensity polymer brush layers with properties dependent on the molecular weight of the dextran side chains.…”