Structure of Polyelectrolyte Brushes in the Presence of Multivalent Counterions

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• 作者：Jing Yu ; Jun Mao ; Guangcui Yuan ; Sushil Satija ; Zhang Jiang ; Wei Chen ; Matthew Tirrell
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：August 9, 2016
• 年：2016
• 卷：49
• 期：15
• 页码：5609-5617
• 全文大小：594K
• 年卷期：0
• ISSN：1520-5835

文摘

Polyelectrolyte brushes are of great importance to a wide range of fields, ranging from colloidal stabilization to responsive and tunable materials to lubrication. We synthesized high-density polystyrenesulfonate (PSS) brushes using surface initiated atom transfer radical polymerization and performed neutron reflectivity (NR) and surface force measurements using a surface forces apparatus (SFA) to investigate the effect of monovalent Na⁺, divalent Ca²⁺, Mg²⁺, and Ba²⁺, and trivalent Y³⁺ counterions on the structure of the PSS brushes. NR and SFA results demonstrate that in monovalent salt solution the behavior of the PSS brushes agrees with scaling theory well, exhibiting two distinct regimes: the osmotic and salted brush regimes. Introducing trivalent Y³⁺ cations causes an abrupt shrinkage of the PSS brush due to the uptake of Y³⁺ counterions. The uptake of Y³⁺ counterions and shrinkage of the brush are reversible upon increasing the concentration of monovalent salt. Divalent cations, Mg²⁺, Ca²⁺, and Ba²⁺, while all significantly affecting the structure of PSS brushes, show strong ion specific effects that are related to the specific interactions between the divalent cations and the sulfonate groups. Our results demonstrate that the presence of multivalent counterions, even at relatively low concentrations, can strongly affect the structure of polyelectrolyte brushes. The results also highlight the importance of ion specificity to the structure of polyelectrolyte brushes in solution.