Screening of a charged particle by multivalent counterions in salty water:Strong charge inversion

Screening of a macroion such as a charged solid particle, a charged membran e, double helix DNA, or actin by multivalent counterions is considered. Sma ll colloidal particles, charged micelles, short or long polyelectrolytes ca n play the role of multivalent counterions. Due to strong lateral repulsion at the surface of the macroion such multivalent counterions form a strongl y-correlated liquid, with the short-range order resembling that of a Wigner crystal. These correlations create additional binding of multivalent count erions to the macroion surface with binding energy larger than k(B)T. As a result even for a moderate concentration of multivalent counterions in the solution, their total charge at the surface of the macroion exceeds the bar e macroion charge in absolute value. Therefore, the net charge of the macro ion inverts its sign. In the presence of a high concentration of monovalent salt the absolute value of inverted charge can be larger than the bare one . This strong inversion of charge can be observed by electrophoresis or by direct counting of multivalent counterions. (C) 2000 American Institute of Physics. [S0021-9606(00)50227-X].