Streaming Current and Effective C-Potential for Particle-Covered Surfaces with Random Particle Distributions

A detailed theoretical and experimental study is presented concerning the streaming current and the derivative effective zeta-potential for a planar surface covered by a monolayer of adsorbed particles. Precise simulation results are obtained for the equilibrium and random-sequential-adsorption (RSA) distributions of monodisperse spherical particles interacting via the excluded-volume potential. The streaming current is calculated in the thin-double-layer regime for all physically accessible particle area fractions. The results are expressed as a linear combination of the interface and particle contributions D-I and D-P weighted by the interface and particle zeta-potentials zeta(I) and zeta(P). We find that in the area-fraction regime where both particle distributions exist, the equilibrium and RSA results for the streaming current are nearly indistinguishable. Our numerical data show that D-I exponentially decays to zero when the particle area fraction theta is increased, whereas D-P exponentially tends to a linear behavior. The results are described (with the accuracy better than 1.5% of the maximal value) by the exponential and linear plus exponential approximations, with only one fitting parameter. The numerical and theoretical predictions are in agreement with experimental data obtained for a wide range of zeta-potentials of the interface and the particles. Results obtained for a rough surface with spherical asperities indicate that the roughness can reduce the effective zeta-potential (as evaluated from the streaming current) by more than 25%; this prediction is also confirmed by experiments.