Dispersion of Silica Fines in Water-Ethanol Suspensions

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Original entry by Hyerim Hwang, AP 225, Fall 2011.

Reference

J. Ren, S. Song, A. Lopez-Valdinieso, J. Shen, and S. Lu, "Dispersion of Silica Fines in Water-Ethanol Suspensions", Journal of Colloid and interface Science 2001 238, 279-284

Keywords

Stability, Silica fines, Water-ethanol suspensions, Solvation film, Hydration forces, Surface forces, Colloids, DLVO theory

Introduction

Figure 1. Schematic diagram of a spherical particle wetted by liquid.
There have been many researches on the dispersion of silica fines in aqueous suspensions but not on the dispersion stability of silica particles in water-ethanol suspensions. Because interaction between silica particles in water-ethanol suspensions is different from that in aqueous solutions, including electrostatic, van der Waals, and structural components, the dipersion behavior of silica fines must be different in water-ethanol suspensions. This study presents the mechanisms which shows a high dispersion stability and investigates the thickness of solvation films on silica particles.
Figure 1. Settling efficiency of silica fines in the suspensions of water, ethanol, and the water-ethanol mixture (1:1) as a function of settling time.
Figure 3. Wetting rate and zeta potential of silica fines in the water-ethanol mixture as a function of the fraction of ethanol.
Figure 2. Settling efficiency of silica fines in the suspension of the water-ethanol mixture as a function of fraction of ethanol.

Results

  • Dispersion of silica

As shown in Figure 1, the settling efficiency increased with increasing settling time. The silica fines exhibit different degrees of dispersion in different liquid media. The strongest dispersion occurs in the water-ethanol suspension, while the weakest is observed in the aqueous. suspension. The results from Figure 2 shows that the different interactions between the silica particles and the liquid media leads silica fines to have different dispersion behavior in different liquids. Plus, Figure 3 shows that the wetting rate increased as the fraction increased, whereas the negative zeta potentials of silica fines steadily decreased when the fraction increased, which means that there is no correlation between zeta potentials and the dispersion of silica fines.

  • Solvation film thickness on silica

A formula has been presented to determine the thickness of the solvation film on the basis of Einstein's theory of viscosity of dispersions, from which the solvation film thickness on silica particles in various liquid mediums have been estimated through the measurement of the suspension viscosity as a function of the volume fraction of the particles.

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Discussion

The results from this paper demonstrates that the dispersion stability of the silica suspensions increased as the fraction of ethanol increased. The stability was stronger in a pure ethanol suspension than in a pure water suspension and it means that stability which is correlated with the lyophilicity of the particles is predominated by the DLVO theory but not by surface charge.