Charged aggregation.

We introduce an aggregation process that begins with equal concentrations of positively and negatively "charged" monomers. Oppositely charged monomers merge to form neutral dimers. These dimers are the seeds for subsequent aggregation events in which neutral clusters of necessarily even mass join irreversibly to form neutral aggregates of ever-increasing size. In the mean-field approximation with mass independent reaction rates, we solve for the reaction kinetics and show that the concentration of clusters of mass k, c_{k}(t), asymptotically scales as A_{k}/t, with A_{k} having a nontrivial dependence on k. We also investigate the phenomenon of gelation in charged aggregation when the reaction rate equals the product of the two incident cluster masses. Finally, we generalize our model to the case of three and more types of monomers.