Application of the DLVO theory for particle deposition problems

Implications of the DLVO theory for problems associated with colloid partic le adsorption and deposition at solid/liquid interfaces were reviewed. The electrostatic interactions between two planar double-layers described by th e classical Poisson-Boltzmann (PB) equation were first discussed. Then, the approximate models for calculating interactions of curved interfaces (e.g. spheres) were exposed in some detail, inter alia the extended Derjaguin su mmation method and the linear superposition approach (LSA), The results ste mming from these models were compared with the exact numerical solution for two dissimilar spheres (including the case of sphere/plane interactions) o btained in bispherical coordinate system. The electrostatic interaction ene rgy was used in combination with dispersion interactions for constructing t he DLVO energy profiles discussed next. The influence of surface roughness and charge heterogeneity on energy profiles was also discussed. It was demo nstrated that in particle deposition problems the monotonically changing pr ofiles determined by the electrostatic interactions played the most importa nt role. In further part of the review the role of these electrostatic inte ractions in adsorption and deposition of colloid particles was discussed. T he governing continuity equation was exposed incorporating the convective t ransport in the bulk and the specific force dominated transport at the surf ace. Approximate analytical models aimed at decoupling of these transfer st eps were described. It was demonstrated that the surface boundary layer app roximation (SFBLA) was the most useful one for describing the effect of ele ctrostatic interaction at initial adsorption stages. A procedure of extendi ng this model for non-linear adsorption regimes, governed by the steric bar rier due to adsorbed particles, was also presented. The theoretical results were then confronted with experimental evidences obtained in the well-defi ned systems, e.g. the impinging-jet cells and the packed-bed columns of mon odisperse spherical particles. The experiments proved that the initial adso rption flux of particles was considerably increased in dilute electrolytes due to attractive electrostatic interactions. This was found in a quantitat ive agreement with the convective diffusion theory. On the other hand, the rate of later adsorption stages was diminished by the electrostatic lateral interactions between adsorbed and adsorbing particles, Similarly, the expe rimental data obtained by various techniques (AFM, reflectometry, optical m icroscopy) demonstrated that these interactions reduced significantly the m aximum monolayer coverages at low ionic strength. This behaviour was found in good agreement with theoretical MC-RSA simulation performed by using the DLVO energy profiles, The extensive experimental evidences seem, therefore , to support the thesis that the electrostatic interactions play an essenti al role in adsorption phenomena of colloid particles. (C) 1999 Elsevier Sci ence B.V. All rights reserved.