Ionic effects on polymers

Abstract

In the conventional theories, ions are usually treated as point charges, and their influences on the properties of polymers are mainly controlled by the ionic strength effect. However, many important phenomena in polymer systems cannot be understood by merely considering the ionic strength effect. This requires us to consider the ionic effects on polymers beyond the influence of ionic strength. Herein, we will discuss the specific ion effect, the ionic hydrogen bond effect, the ionic hydrophilicity/hydrophobicity effect, and the multivalent ion effect in polymer systems. The specific ion effect exists in various charged and neutral polymer systems, and can be observed in different types of solvent systems. The ionic hydrophilicity/hydrophobicity effect can be used to modulate many important properties of strong polyelectrolyte brushes including hydration, wettability, and adhesion. The ionic hydrophilicity/hydrophobicity effect can be applied to tune not only the properties of the surface-grafted polyelectrolytes, but also the properties of the polyelectrolyte solutions and hydrogels. The multivalent ion effect can be used to control the properties of polyelectrolyte brushes and polymer hydrogels through the electrostatic crosslinking interactions. The ionic effects on polymers demonstrated here would widen and deepen our understanding of the interactions between ions and polymers, forming a basis for tuning the polymer properties with ions, and can be further expanded to other types of important ion-polymer interactions.