  Due to the strong correlations between multivalent counterions condensed on a
macroion, the net macroion charge changes sign at some critical counterion
concentration. This effect is known as the charge inversion. Near this critical
concentration the macroion net charge is small. Therefore, short range
attractive forces between macroions dominate Coulomb repulsion and lead to
their coagulation. The kinetics of macroion coagulation in this range of
counterion concentrations is studied. We calculate the Coulomb barrier between
two approaching like charged macroions at a given counterion concentration. Two
different macroion shapes (spherical and rod-like) are considered. A new
"self-regulated" regime of coagulation is found. As the size of aggregates
increases, their charge and Coulomb barrier also grow and diminish the sticking
probability of aggregates. This leads to a slow, logarithmic increase of the
aggregate size with time.
