ROLE OF ELECTROSTATIC INTERACTIONS IN PARTICLE ADSORPTION

The role of the electrostatic double-layer interactions in adsorption of colloid particles at solid/liquid interface was reviewed. The pheno menological formulation of the governing PB equation was presented wit h the expressions for the pressure tensor enabling one to calculate fo rces, torques and interaction energies between particles in electrolyt e solutions. Then, the limiting analytical results for an isolated dou ble-layer (both spherical and planar) were discussed in relation to th e effective surface potential concept. The range of validity of the ap proximate expression connecting the surface potential and the effectiv e surface potential with surface charge for various electrolytes was e stimated. The results for double-layer systems were next presented inc luding the case of two planar double-layers and two dissimilar spheric al particles. Limiting solutions for short and long distances as well as for low potentials (linear HI-IF model) were discussed. The approxi mate models for calculating interactions of spheres, i.e., the extende d Derjaguin summation method and the linear superposition approach (LS A) were also introduced. The results stemming from these models were c ompared with the exact numerical solution obtained in bispherical coor dinate system. Possibilities of describing interactions of nonspherica l particles (e.g., spheroids) in terms of the Derjaguin and the equiva lent sphere methods were pointed out. In further part of the review th e role of these electrostatic interactions in adsorption of colloid pa rticles was discussed. Theoretical predictions were presented enabling a quantitative determination of both the initial adsorption flux for low surface coverages and the surface blocking er surface coverages. P ossibility of bilayer adsorption for dilute electrolytes was mentioned . The theoretical results concerning both the adsorption kinetics and structure formation were then confronted with experimental evidences o btained in the well-defined systems, e.g.,the impinging-jet cells and the packed-bed columns of monodisperse spherical particles. The experi ments proved that the initial adsorption flux was considerably increas ed in dilute electrolytes whereas the monolayer coverages were conside rably decreased due to lateral interactions among particles. It was th en concluded that the good agreement between experimental and theoreti cal data confirmed the thesis of an essential role of the electrostati c interactions in adsorption phenomena of colloid particles.