Crucial Nonelectrostatic Effects on Polyelectrolyte Brush Behavior

Polyelectrolyte brushes have received extensive attention due to their swelling behavior in aqueous solutions, which is a result of their ionic nature and nonelectrostatic (polymer-polymer and polymer-solvent) interactions. While the nonelectrostatic contributions are typically assumed to be negligible compared to the ion osmotic pressure, we present herein a systematic investigation of how the nonelectrostatic interactions dramatically affect the swelling behavior of polyelectrolyte brushes. Using a modular synthesis procedure, polyelectrolyte brushes with similar chain lengths, grafting densities, and charge densities but with various side chains were synthesized. The swelling behaviors of the brushes were then thoroughly investigated as a function of grafting density and ionic strength using ellipsometry. A theoretical mean-field approach was also developed to quantify the contributions of the ion osmotic and nonelectrostatic effects. Accordingly, it was both experimentally and theoretically demonstrated how fundamentally different swelling behaviors can exist depending on the relative contributions of ion osmotic and nonelectrostatic effects. This new insight reveals new opportunities for applications of polyelectrolyte brushes based on their tunable hydrophobicity and provides new ideas for fundamental investigations of these systems.

Automated summary

This study systematically investigated how nonelectrostatic interactions dramatically affect the swelling behavior of polyelectrolyte brushes, revealing fundamentally different swelling behaviors depending on the relative contributions of ion osmotic and nonelectrostatic effects. The results provide new opportunities for applications of polyelectrolyte brushes based on their tunable hydrophobicity and suggest new ideas for fundamental investigations of these systems.