  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.
