Effect of Counterion-Mediated Hydrogen Bonding on Polyelectrolytes at the Solid/Water Interface: Current Understanding and Perspectives.

The counterion-mediated hydrogen bonding (CMHB) effect can be generated in polyelectrolyte systems when hydrogen bonds are formed between the bound counterions and polyelectrolyte chains. This Perspective mainly discusses the effect of CMHB on polyelectrolytes at the solid/water interface. The CMHB effect generated by the hydroxide (OH) or hydronium (HO) counterions gives rise to a pH responsiveness of strong polyelectrolyte brushes (SPBs) whose strength can be modulated by the external salt concentration. Further studies have shown that the CMHB effect on SPBs can be extended beyond the OH and HO counterions and that the CMHB effect can be observed in the systems of weak polyelectrolyte brushes (WPBs) and polyelectrolyte multilayers (PEMs). Based on the understanding of the mechanisms of the CMHB effect on polyelectrolytes at the solid/water interface, we have demonstrated that a range of important properties of SPBs, WPBs, and PEMs can be tuned by pH with the consideration of the CMHB effect. Future directions for the CMHB effect on polyelectrolytes are also discussed. The insights on the CMHB effect on polyelectrolytes at the solid/water interface would promote the development of smart interfacial polyelectrolyte materials in a wide range of fields.