(461g) Controlled Particle Deposition by Design of An Electrochemical Adsorption Cell

Deposition of colloidal particles on to a substrate takes place in two stages : (1) transport stage wherein the particles are brought into the vicinity of the collector by bulk fluid flow or diffusion; (2) attachment process wherein the particle is physically deposited. The attachment stage is governed by colloidal interaction forces such as London van der Waals, electrical double layer, Born repulsion , hydration hydrophobic interactions . In the theoretical section of this work it will be assumed that the main energies contributing to adsorption interaction between the surfaces will be due to electrical double layer and the van der Waals attraction . The sum of these energies provides the total interaction energy between surfaces and this constitutes the underlying assumption for the classical D.L.V.O. theory of colloidal stability.Predictions based on the D.L.V.O. theory suggest the occurrence of favorable and unfavorable deposition conditions when overall attractive and repulsive energies exist between surfaces respectively . Indeed many experimental results in the literature confirm the occurrence of favorable and unfavorable deposition conditions. However , The D.L.V.O. theory suffers from a few shortcomings discussed by Elimelech et .al . discuss the deposition studies in the literature and point out that ideal collectors and particles are usually used for investigation of deposition processes . Ideal particles are smooth, spherical , mono disperse with narrow size distribution . Ideal collectors used are parallel plate, stagnation point flow, bed of glass beads and these provide hydrodynamics and interaction energies that can be described within the existing framework . It was mentioned that the deposition process consists of two main stages i.e. transport and deposition stages. The transport stage may occur by bulk fluid flow , interception, sedimentation under the . influence of gravity, inertial impaction and diffusion. For non ? Brownian particles the diffusion process becomes negligible compared to the bulk fluid flow . The polystyrene latex particles used in this study were 5.4 Micrometer and hence effect of diffusion becomes negligible. For reasonably low flow rates, Re Conclusion For the present experimental conditions the main forces contributing to the deposition process are the surface forces and hydrodynamics. At the highest flow rate of 34 cm3 .min1 the colloidal forces were shown to be negligible compared to the hydrodynamics. Indeed the effect of surface forces at the KCI concentration of 0.001 mol/ dm3 apparently only became significant at flow rate of 1.7 cm3/min . At this flow rate and KCI concentration of 0.001 mol/dm3 the experimental results show clear evidence of conditions governing the occurrence of favorable and unfavorable deposition conditions. The variation of collector potential under unfavorable deposition condition dos not reduce large changes in the deposition rate whereas variation of collector potential under favorable conditions produce significant changes in the deposition rate. At collector potentials of -300 mV vs. SCE hydrogen evolved and this was accompanied by a rise in the pH of the solution. This rise in pH affected the zeta potential of the particles though slight but significant.