FLUCTUATIONS IN THE NUMBER OF PARTICLES ADSORBED UNDER THE INFLUENCE OF DIFFUSION AND FLOW

Fluctuations in the number of colloid particles adsorbed irreversibly under diffusion and flow were determined. The experimental measurement s were carried out in the impinging-jet cells using as model colloids the monodisperse polystyrene latex particles of micrometer size range adsorbing at mica sheets. The surface concentration of adsorbed partic les was determined quantitatively using the direct microscope observat ion method coupled with an image analyzing system. Two series of exper iments were performed (i) for diffusion controlled adsorption when the random sequential adsorption (RSA) mechanism was valid and (ii) for f low controlled adsorption. It was found that in the case of RSA the re duced variance of the distributions decreased markedly for increasing surface concentration theta in accordance with theoretical predictions based on the mean-field approximation. The experimental results were in a good agreement with the numerical simulations performed according to the RSA algorithm. It was also determined that the magnitude of fl uctuations in our irreversible system was very similar to reversible s ystems described by the scaled-particle theory. A significantly differ ent behavior was observed for flow affected adsorption when the reduce d variance (at the same surface concentration) was much smaller than f or the RSA model, therefore deviating considerably from an equilibrium system. The decrease in the variance indicated that the surface exclu sion effects (described by the available surface function) were more i mportant under flow due to the hydrodynamic scattering effect. (C) 199 6 American Institute of Physics.