ACCURATE ANALYTIC FORMULAS FOR THE DOUBLE-LAYER INTERACTION BETWEEN SPHERES

Very simple but accurate analytic formulas are presented for the elect rical double-layer force and interaction free energy between two spher ical colloidal particles, valid up to the moderate to high-potential r egime. These formulas represent a remarkable improvement on previous a nalytic and semianalytic formulas for the interaction, while maintaini ng an excellent degree of analytic simplicity. Furthermore, a detailed derivation of the interaction free energy between two dissimilar sphe res in the linear Debye-Huckel approximation is presented that is vali d for all kappa h, where kappa is the Debye screening parameter and h is the distance of closest approach between the spheres. In doing so, it is demonstrated that the well-known Hogg-Healy-Fuersteneau (HHF) fo rmula, which is valid only in the small Kh regime, may be trivially mo dified to extend its range of applicability to all Kh. (C) 1995 Academ ic Press, Inc.