Journal of Colloid and Interface Science, Vol.183, No.1, 124-130, 1996
A Network Model of the Electrical Double-Layer Around a Colloid Particle
A network method, based on the theory of Network Thermodynamics, is applied in this work to the computation of electric potential, ionic concentration, and charge density of the double layer around a spherical colloid particle, It is demonstrated that the nonlinear Poisson-Boltzman equation is formally equivalent to the equations governing currents and voltages in a properly designed electric circuit, obtained as the series association of subcircuits corresponding to each volume element of the double layer. It is found that the reduced electric potential at any point of the double layer corresponds to a voltage at the corresponding circuit element, whereas the surface charge density is essentially proportional to the current at a certain point of the network. A simulation program is used to solve the circuit in order to obtain potential and ion concentration profiles, as well as surface charge density. All computations can be easily done for arbitrary values of surface potential, particle radius, and ionic concentrations and valencies. The results are compared to those tabulated by Loeb et al. ("The Electrical Double Layer Around a Spherical Colloid Particle." MIT Press, Cambridge, MA, 1961) when it is possible, and an excellent agreement with relative deviations below 0.1% is found in all cases. The method proves to be quite general and extremely efficient, as well as applicable to a great variety of double layer compositions.