Spontaneous and Flow-Driven Interfacial Phase Change: Dynamics of Microemulsion Formation at the Pore Scale

Abstract

The dynamic behavior of microemulsion-forming water-oil-amphiphiles mixtures is investigated in a 2.5D micromodel. The equilibrium phase behavior of such mixtures is well-understood in terms of macroscopic phase transitions. However, what is less understood and where experimental data are lacking is the coupling between the phase change and the bulk flow. Herein, we study the flow of an aqueous surfactant solution-oil mixture in porous media and analyze the dependence of phase formation and spatial phase configurations on the bulk flow rate. We find that a microemulsion forms instantaneously as a boundary layer at the initial surface of contact between the surfactant solution and oil. The boundary layer is temporally continuous because of the imposed convection. In addition to the imposed flow, we observe spontaneous pulsed Marangoni flows that drag the microemulsion and surfactant solution into the oil stream, forming large (macro)emulsion droplets. The formation of the microemulsion phase at the interface distinguishes the situation from that of the more common Marangoni flow with only two phases present. Additionally, an emulsion forms via liquid-liquid nucleation or the Ouzo effect (i.e., spontaneous emulsification) at low flow rates and via mechanical mixing at high flow rates. With regard to multiphase flow, contrary to the common belief that the microemulsion is the wetting liquid, we observe that the minor oil phase wets the solid surface. We show that a layered flow pattern is formed because of the out-of-equilibrium phase behavior at high volumetric flow rates (order of 2 m/day) where advection is much faster than the diffusive interfacial mass transfer and transverse mixing, which promote equilibrium behavior. At lower flow rates (order of 30 cm/day), however, the dynamic and equilibrium phase behaviors are well-correlated. These results clearly show that the phase change influences the macroscale flow behavior.

Effect of hydrophobically modified PEO polymers (PEO-dodecyl) on oil/water microemulsion properties: in vitro and in silico investigations

“…[14][15][16][17] The interfacial lm formed by the surfactant molecules is characterized by its tension, its rigidity, and its spontaneous curvature. [18][19][20][21] Their relative importance depends on the stresses undergone by the lm which determines the physical properties of microemulsions such as their phase behavior, their stability, their structure, and their solubilization capacity. [22][23][24][25] Although there are still few products on the market, microemulsions exhibit remarkable properties, in particular an ultralow water/oil interfacial tension 26,27 and a high solubilizing power both towards hydrophilic and lipophilic compounds.…”

Interfacial Rheology Measured with a Spinning Drop Interfacial Rheometer: Particularities in More Realistic Surfactant–Oil–Water Systems Close to Optimum Formulation at HLDN = 0

“…These lenses appear around the oil drops but do not cover the whole drop. Indeed, the microemulsion phase does not wet the oil–water interface (Abillon et al, 1991; Chatenay et al, 1985; Kahlweit et al, 1990; Sottmann and Strey, 1997; Tagavifar et al, 2017; Widom, 1987). During the spinning drop elongation, the lens is stretched and might affect the elastic response.…”

How the Influence of Different Salts on Interfacial Properties of Surfactant–Oil–Water Systems at Optimum Formulation Matches the Hofmeister Series Ranking

“…It is worth noting that the phase angle decreases to low values at optimum formulation in the Winsor III region, being lower for the systems with chaotropic ions (NH 4 + , NO 3 − ). This can be explained by the occurrence of a nonwetting behavior by the middle‐phase microemulsion at HLD = 0 (Abillon et al, ; Aratono and Kahlweit, ; Tagavifar et al, ), which might generate an elastic response due to the stretching of microemulsion lenses during the spinning drop elongation (Chen et al, ; Widom, ), even if the amount of microemulsion present is very small (Marquez et al, ).…”