A Non-stoichiometric Universality in Microbubble-Polyelectrolyte Complexation

TL;DR

This study explores the electrical properties of microbubbles encapsulated with oppositely charged polyelectrolytes, revealing unusual overcharging behaviors that challenge traditional stoichiometric expectations.

Contribution

It uncovers a non-stoichiometric universality in microbubble-polyelectrolyte complexation, supported by experimental observations and a theoretical model explaining overcharging phenomena.

Findings

Overcharging occurs at concentrations independent of polyelectrolyte chain length.

Overcharging concentrations are much larger than neutralization points.

A theoretical model explains the inefficient charge-reversal through adsorption-desorption kinetics.

Abstract

We investigated the fundamental electrical properties of microbubbles (MBs) that are directly encapsulated by the addition of oppositely charged polyelectrolytes (PEs). Charge-reversal of the MB-PE complex particles has been observed by the microscopic electrophoresis method, revealing unusual overcharging behaviors in MB-PE complex solutions, as follows. The critical concentrations of cationic PEs added for overcharging were not only independent of their chain lengths and molecular species, but also much larger than stoichiometric neutralization points. Thus, we provide a theoretical sketch that considers the adsorption-desorption kinetics of small anions on the surface of genuine microbubbles, which can explain the inefficient charge-reversal.