LONG-RANGE ELECTROSTATIC ATTRACTION BETWEEN LIKE-CHARGE SPHERES IN A CHARGED PORE

The existence of long-range attractive electrostatic forces between pa rticles of like charge is one of the great current controversies of co lloid science. The established theory (Dejaguin-Landau-Vervey-Overbeek ; DLVO) of colloidal interactions predicts that an isolated pair of li ke-charged colloidal spheres in an electrolyte should experience a pur ely repulsive screened electrostatic (coulombic) interaction(1,2). Dir ect measurements of such interactions have shown quantitative agreemen t with DLVO theory(3-5). Recent experiments, however, provide evidence that the effective interparticle potential can have a long-range attr active component in more concentrated suspensions(6,7) and for particl es confined by charged glass walls(3,5,8-10). It is apparent that the long-range attraction in concentrated systems is due to multi-body int eractions and may have a similar explanation to the attraction observe d for otherwise confined colloids. Theoretical explanations have been proposed(11-13) but remain the subject of controversy(14-15). Here we present a quantitative theoretical explanation of these attractive for ces between confined colloidal particles, based on direct solutions of the nonlinear Poisson-Boltzmann equation for two like-charged spheres confined in a cylindrical charged pore. The calculations show that th e attraction may be explained by the redistribution of the electric do uble layers of ions and counterions in solution around the spheres, ow ing to the presence of the wall; there is thus no need to revise the e stablished concepts underlying theories of colloidal interactions.