Abstract

Depositions of negatively charged polystyrene particles in a parallel plate flow chamber to negatively and positively charged collector surfaces are compared at different shear rates and ionic strengths. The observation of adhering particles was done in situ during the deposition process with the aid of an image analyzer and the adsorption and desorption of each particle was monitored individually using a special tracking algorithm. Initial deposition rates j(0)(EXP) were higher to positively charged glass than to negatively charged glass collector surfaces, depending on shear rates and ionic strength. All observed experimental deposition rates were, however, smaller than the Smoluchowski-Levich (SL) approximate solution of the convective-diffusion (CD)equation. Initial deposition rates were also calculated using an exact numerical solution of the CD equation; they were two times higher than the experimentally observed deposition rates for positively charged glass and about equal or lower for negatively charged glass. The desorption rates j(des)(t) Of polystyrene particles on positively charged glass were nearly zero under all conditions, whereas the desorption rates from the negatively charged glass were considerable and finally balanced the adsorption rates j(ads)(t). From the residence time dependent desorption probability beta(t - tau), it could be determined that polystyrene particles on negatively charged collector surfaces have the highest probability of desorption within the first 5-10 min after deposition. Experimental results were subsequently compared with those from a proposed adsorption-desorption model for deposition kinetics, using the parameters derived as an input, and with a Monte Carlo simulation of the deposition process. A high degree of similarity between experimental results, the adsorption-desorption model and the Monte Carlo simulation results was observed, which indicates; the consistency of the applied experimental methods and theoretical models.

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