The electrokinetic behaviour of surfaces modified by particle adsorption

The adsorption of particles on an oppositely charged surface modifies the e lectrokinetic behaviour of the latter. In general the extent of this modifi cation is observed to vary monotonically with particle coverage. In this ma nuscript a number of simple models are examined to quantitatively explain t his behaviour. The models are essentially empirical and aim to relate the r eadily measured parameters of the component particles and surfaces, such as the zeta potentials (zeta), particle size, particle coverage (theta) and D ebye length, to the zeta potential of the surface with adsorbed particles. The models are applied to the adsorption of silica particles on aminopropyl silane modified glass and also to other previously reported experimental da ta. It is clear that the surface of shear does not closely follow the topog raphy of the particle adsorbed surface. The experimental zeta/theta data ca n be predicted only when the shear plane adjacent to the particle-free area s of the surface is shifted away from the surface. For silica particles the shift required is linearly related to particle coverage and exceeds one ha lf of a particle diameter at coverages of 0.35. The most refined model can predict the experimentally measured particle size and ionic strength depend ence of the zeta potential for surfaces with adsorbed particles. The model may also be used to predict the effect of roughness on electrokinetic behav iour, by applying it to the case of a chemically symmetric particle/surface combination. (C) 1999 Elsevier Science B.V. All rights reserved.