Approximate expression for interaction of a two similar plane double layer at moderate and low potential

摘要

The interaction energy between two similar plane parallel double layers is expanded in a series of tanh y(0)/4 and a general expression is introduced. The series converges very fast at moderate and low potentials. With the first four terms of the series a very high precision with six significant figures can be reached when the dimensionless surface potential y(0) of the colloidal particles is less or equal to 3.