The electrokinetic behaviour of surfaces modified by particle adsorption

Abstract

The adsorption of particles on an oppositely charged surface modifies the electrokinetic behaviour of the latter. In general the extent of this modification is observed to vary monotonically with particle coverage. In this manuscript a number of simple models are examined to quantitatively explain this behaviour. The models are essentially empirical and aim to relate the readily measured parameters of the component particles and surfaces, such as the zeta potentials ( ζ), particle size, particle coverage ( θ) and Debye length, to the zeta potential of the surface with adsorbed particles. The models are applied to the adsorption of silica particles on aminopropylsilane modified glass and also to other previously reported experimental data. It is clear that the surface of shear does not closely follow the topography of the particle adsorbed surface. The experimental ζ/ θ data can be predicted only when the shear plane adjacent to the particle-free areas of the surface is shifted away from the surface. For silica particles the shift required is linearly related to particle coverage and exceeds one half of a particle diameter at coverages of 0.35. The most refined model can predict the experimentally measured particle size and ionic strength dependence of the zeta potential for surfaces with adsorbed particles. The model may also be used to predict the effect of roughness on electrokinetic behaviour, by applying it to the case of a chemically symmetric particle/surface combination.