(251aa) Conformations and Interfacial Properties of Weak Polyelectrolyte Brushes: Effect of Chain Architecture

Weak polyelectrolyte (PE) brushes of tunable ionization show great potential as “smart” polymer materials for diverse applications from drug delivery to energy storage. The conformational structure and resulting interfacial properties of weak polyelectrolyte brushes exhibit strong dependence on solution conditions, such as pH and ionic strength, as well as polymer chain architectures. In this work, we investigate the swelling characteristics of polycationic brushes of linear and branched poly(2-vinyl pyridine) (P2VP) chains immersed in aqueous solutions of varied pH and added ions. The critical transition pH, at which stretched P2VP brush chains collapse with a resulting increase in P2VP surface hydrophobicity, is determined in aqueous solutions by AFM or fluorescence spectroscopy. The collapse of P2VP brushes occurs over a broad pH range, in sharp contrast to the first-order-like conformational transition of linear free P2VP chains in aqueous solution. The swelling degree of surface-tethered linear P2VP brushes is found to be much greater than that of branched brushes under the similar protonation degree, possibly due to the difference in brush grafting density. Distinct scaling behaviors of P2VP brush thickness with counterion concentration are also examined.