Interaction of two similar plane double layers for z+/z− = −1/2 asymmetric electrolytes at positive surface potential

The interaction energies between two similar plane double-layers for z+/z− = −1/2 asymmetric electrolytes at positive surface potential are expanded in the power series at lower potential and smaller absolute value of integral constant as well as higher potential and larger absolute value of integral constant, respectively. When dimensionless surface potential y0 is less or equal to 20, the number of the series terms required to obtain the interaction energies with six significant figures are not more than 5 if high potential expressions are combined with low potential expressions. The accurate numeral results are given and they can be used to check up the validity of approximate expressions people obtain. The present results are also fit for z+/z− = −2 asymmetric electrolytes at negative surface potential.