Salt dependence of the tribological properties of a surface-grafted weak polycation in aqueous solution

Maryam Raftari, Zhenyu Zhang, Steven Carter, GJ Leggett, Mark Geoghegan

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Abstract

The nanoscopic adhesive and frictional behaviour of end-grafted poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with gold- or PDMAEMA-coated atomic force microscope tips in different potassium halide solutions with concentrations up to 300 mM is a strong function of salt concentration. The conformation of the polymers in the brush layer is sensitive to salt concentration, which leads to large changes in adhesive forces and the contact mechanics at the tip-sample contact, with swollen brushes (which occur at low salt concentrations) yielding large areas of contact and friction-load plots that fit JKR behaviour, while collapsed brushes (which occur at high salt concentrations) yield sliding dominated by ploughing, with conformations in between fitting DMT mechanics. The relative effect of the different anions follows the Hofmeister series, with I– collapsing the brushes more than Br– and Cl– for the same salt concentration.
Original languageEnglish
JournalTribology Letters
Volume66
Issue number11
Early online date5 Dec 2017
DOIs
Publication statusPublished - Mar 2018

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