Counterion Condensation of Polyelectrolytes and the Electrophoretic Behavior

Abstract

The origin and the historical development of the concept of the counterion condensation is described with the emphasis that the concept is inherent to the polyions in rodlike geometr y. A couple of experimental results on the microscopic state of the condensed counterions are also discussed. Ef fects of added salt are discussed in terms of the additivity rule. In the second par t, three characteristic aspects of the electrophoretic behavior of polyions are described. (1) The free-draining behavior, (2) Negative stoichiometric transference number of counterions, and (3) The saturation behavior of the mobility with respect to the charge numbers. The last two proper ties are considered to be due to the counterion condensation. In the final par t, arguments are presented regarding the extension of the counterion condensation concept to colloid ions in general, beyond the rod-like geometr y. Three operational definitions of the counterion condensation are proposed.