SURFACE ELEMENT INTEGRATION - A NOVEL TECHNIQUE FOR EVALUATION OF DLVO INTERACTION BETWEEN A PARTICLE AND A FLAT-PLATE

A novel method, the surface element integration (SEI), is developed to determine the van der Waals and electrostatic double layer interactio ns between a particle and an infinite flat plate from the correspondin g interactions per unit area between two infinite flat plates. Compari son with the Hamaker expression for nonretarded van der Waals interact ion reveals that the new technique gives the exact interaction energy between a spherical particle and a flat plate. Available analytical ex pressions for the electrostatic double layer interaction energy betwee n two infinite flat plates, based on the linearized Poisson-Boltzmann equation, are used in SEI to obtain the sphere-flat plate interaction energy. These sphere-hat plate interaction energies determined using S EI are compared with the corresponding interaction energies obtained f rom a detailed numerical solution of the Poisson-Boltzmann equation ba sed on finite element analysis. The comparisons reveal that SEI scales the flat plate interaction to the corresponding sphere-flat plate geo metry exactly, while the scaling based on the conventional Derjaguin a pproximation technique grossly overpredicts the interaction energy for small particles and low electrolyte concentrations. (C) 1997 Academic Press.