| Abstract
| - Dissipative particle dynamics (DPD) was used to investigate the behavior of two opposing end-grafted chargedpolymer brushes in aqueous media under normal compression and lateral shear. The effect of polymer molecularweight, degree of ionization, grafting density, ionic strength, and compression on the polymer conformation and theresulting shear force between the opposing polymer layers were investigated. The simulations were carried out forthe poly(tert-butyl methacrylate)-block-poly(sodium sulfonate glycidyl methacrylate) copolymer, referred as PtBMA-b-PGMAS, end-attached to a hydrophobic surface for comparison with previous experimental data. Mutual interpenetrationof the opposing end-grafted chains upon compression is negligible for highly charged polymer brushes for compressionratios ranging from 2.5 to 0.25. Under electrostatic screening effects or for weakly charged polymer brushes, asignificant mutual interpenetration was measured. The variation of interpenetration thickness with separation distance,grafting density, and polymer size follows the same scaling law as the one observed for two opposing grafted neutralbrushes in good solvent. However, compression between two opposing charged brushes results in less interpenetrationrelative to neutral brushes when considering equivalent grafting density and molecular weight. The friction coefficientbetween two opposing polymer-coated surfaces sliding past each other is shown to be directly correlated with theinterpenetration thickness and more specifically to the number of polymer segments within the interpenetration layer.
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