title: Interactions between Polyelectrolyte Brushes and Hofmeister Ions: Chaotropes versus Kosmotropes.
abstract: We have investigated the interactions between the positively charged poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) brushes and the Hofmeister anions and the interactions between the negatively charged poly(3-sulfopropyl methacrylate potassium) (PSPMA) brushes and the Hofmeister cations using a combination of quartz crystal microbalance with dissipation and spectroscopic ellipsometry. A V-shaped anion series is observed in terms of the ion-specific interactions between the PMETAC brushes and the Hofmeister anions. We have found that the chaotropic and kosmotropic anions interact with the PMETAC brushes in different manners. The ion-specific interactions between the PMETAC brushes and the chaotropic anions are dominated by the direct interactions between the anions and the positively charged quaternary ammonium group via ion pairing mediated by ionic hydration strength or polarizability, whereas the ion-specific interactions between the PMETAC brushes and the kosmotropic anions are dominated by the competition for water molecules between the anions and the brushes. The ion-specific interactions between the PMETAC brushes and the anions have significant influences on both the hydration and the conformation of the brushes. The cations exhibit weaker specific ion effects on the PSPMA brushes in comparison with the specific anion effects on the PMETAC brushes.
authors.affiliation: Department of Chemical Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China , Hefei, P. R. China 230026.
authors.forename: Ran
authors.initials: R
authors.lastname: Kou
authors.affiliation: Department of Chemical Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China , Hefei, P. R. China 230026.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Chemical Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China , Hefei, P. R. China 230026.
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.affiliation: Department of Chemical Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China , Hefei, P. R. China 230026.
authors.forename: Guangming
authors.initials: G
authors.lastname: Liu
mesh_terms: D000838:Anions / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry*; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D058525:Quartz Crystal Microbalance Techniques; D013499:Surface Properties
chemical_list: D000838:Anions; D004573:Electrolytes; D011108:Polymers