A positively charged, mixed bilayer vesicle in the presence of negatively
charged surfaces (for example, colloidal particles) can spontaneously partition
into an adhesion zone of definite area, and another zone that repels additional
negative objects. Although the membrane itself has nonnegative charge in the
repulsive zone, negative counterions on the interior of the vesicle
spontaneously aggregate there, and present a net negative charge to the
exterior. Beyond the fundamental result that oppositely charged objects can
repel, our mechanism helps explain recent experiments on surfactant vesicles.Comment: Latex using epsfig and afterpage; pdf available at
http://www.physics.upenn.edu/~nelson/Mss/repel.pd
