Stabilisation of emulsion droplets by fine powders

Abstract

Finely divided solids can stabilize emulsion droplets provided the solids are partially wetted by both the disperse liquid phase and the continuous liquid phase. The stabilisation of oil/water emulsions by finely divided solids in the presence of suitable organics has been related to the three phase (solid/oil/water) contact line. Schulman and Leja (1954a) and Taubman and Koretskii (1965) provide evidence that O/W emulsions are formed when the contact angle is less than 90° but inversion occurs to W/O emulsions when the contact angle exceeds 90°. We present a thermodynamic study of emulsion stabilization by finely divided solids, which is an extension of an earlier theory by Van der Minne (1928) who neglected interactions among the particles and droplets and also entropy effects due to Brownian motion. Only stable W/O emulsions are considered here. The starting point of the theory is an expression for the Helmholtz free energy associated with the oil/water interfaces stabilized by finely divided solids in the presence of surfactants. By minimising this free energy, it is shown that in a stable emulsion almost all the solid particles are adsorbed at the oil/water interface of the oil drops. This accounts for the experimental result that the average size of oil droplets decreases with increase in the concentration of solids. A particular example of emulsion stabilization by solids occurs in the hot water extraction process on the Athabasca oil sands. Both clay particles and anionic surfactants act as stabilizers of the bitumen droplets suspended in an aqueous alkaline environment.

Oilfield solids and water-in-oil emulsion stability

“…A decrease in the average drop size tends to result in more stable emulsions. Free energy considerations support these observations [36].…”

Effect of charged colloidal particles on adsorption of surfactants at oil–water interface

“…In these systems, fine solids, through surfactant adsorption, can act as a stabilizer of either oil-in-water or water-in-oil emulsions, depending on the nature of the fine solids and surfactants [3]. The unpredictive nature of solids in a complex system increases the difficulty of the desired phase separation [4][5][6]. In Canadian Athabasca oil sands processing, for example, Gewers [7] reported the formation of colloidal clay "skins" at the oil-water interface and its effect on the emulsion stability.…”

Surface and interfacial tensions of aqueous dispersions of charged colloidal (clay) particles

“…2 and 8). Levine et al (9)(10)(11) have provided a theoretical analysis of the stabilization of emulsions by fine particles at the interface, including some specific consideration of the bitumen-water interface. Menon et al (12)(13)(14)(15)(16)(17) have published several accounts of their investigations of emulsions stabilized by finely divided solids; these papers provide convincing evidence that such solids can have important effects on interfacial tensions.…”