Deposition of latex particles on alumina fibers

The deposition of sub-micron latex particles during flow through beds of fine alumina fibers has been studied as a function of pH and ionic strength in the vicinity of the fiber isoelectric point (i.e.p.). Conditions were chosen so that the predominant capture mechanism was diffusion. Results have been compared with the “classical” theory of convective diffusion to cylinders and with modern theory, which takes into account colloidal and hydrodynamic interactions between particles and collector.Initial fiber collection efficiencies, determined at the i.e.p. where the fibers bear no surface charge, are considerably lower than those predicted by classical theory and are insensitive to ionic strength. This lack of dependence on ionic strength suggests that neither constant potential nor constant charge conditions are maintained during particle-fiber encounters and that some intermediate condition is more appropriate. Particle capture results obtained at pH values above and below the fiber i.e.p. agree qualitatively with the predictions of the Spielman and Friedlander “surface reaction” model, although this is not strictly valid below the i.e.p. where the fibers are positively charged and there is no repulsion barrier. Under these conditions a significant enhancement of capture efficiency is observed at low ionic strength, as a result of double layer attraction. Above the i.e.p., where the fibers and particles are both negatively charged, double layer repulsion causes a large reduction in capture efficiency, although the predicted is even larger.The saturation coverage of the fibers by deposited particles was found to decrease strongly as the ionic strength was decreased, indicating the importance of lateral interactions between particles.