Deposition of colloidal spheres under quiescent conditions

Chai Geok Tan
The phenomenon of deposition (or release) of fine particles or other microscopic species, suspended in a liquid, onto (or from) a foreign substrate surface plays a critical role in many natural and industrial processes. Traditionally, the analysis of this phenomenon has been conceptually divided into two steps — the transport step and the adhesion step. Attempts to understand the role of the adhesion step on the overall deposition process under most practical situations are complicated by the
more » ... esence of a large number of interdependent parameters such as double layer thickness, particle and wall zeta-potential, particle size and flow, amongst others. Thus, as a first step towards gaining a better understanding of the phenomenon, an experimental study of a very simple deposition system, where only the random nature of the deposition process and the double layer interactions between deposited particles are important, was undertaken. In this idealized system, a stable suspension of monodispersed, negatively charged colloidal silica spheres one micron in diameter, suspended in an aqueous medium in a specially constructed deposition cell, were allowed to settle by gravity and be deposited permanently onto a cationic polymer-coated glass cover slip. The magnitude of surface potential was altered by adjusting the pH of the suspension using NaOH and HC1, while the electrical double layer thickness was varied by dissolving different predetermined quantities of KC1 into the suspension. The results showed that the trends in the experimental surface coverages obtained were in accordance with expectation in that as the double layer thickness, 1/К, or the particle zeta potential, ζ⍴' , increased (leading to an increase in the interaction energy between the particles), the surface coverage decreased. Furthermore, the extent of surface coverages obtained when both 1/К and ζ⍴ were changed was found to be greater than that when 1/К alone was used as the controlling variable. A separate series of studies examining the effect of [...]
doi:10.14288/1.0058839 fatcat:nxz6o2vburdnbkvrvzsuygvfgy