Electrostatic repulsion of positively charged vesicles and negatively charged objects

Opposite charged objects attract each other in vacuum; same thing happens in solution according to Possion-Boltzmann theory. Yet it was observed in the experiment that a positively charged, mixed bilayer vesicle with the presence of negatively charged colloidal particles can spontaneously partition into an adhesion zone with some area and another zone that repels additional negative objects. An adhesion saturation theory based on the Possion-Boltzmann theory was formulated to explain this phenomenon. Although the membrane is strictly positively charged because it\u27s a mixture of positively charged and neutral surfactants, the counterions inside membrane can move laterally. The membrane charges along with inside counterions can partially de-mix into two regions by thermal instability. One region attracts more charged surfactants from the other region, and also attracts some positive counterions inside the membrane and renders the other region repulsive to additional incoming negative objects. This thermal instability is strongest for thin impermeable membrane case. It is weakened but still exists for finite thickness membrane. And several improvements of mean-field PB theory are considered and the instability is robust under those modifications