Flow instabilities due to the interfacial formation of surfactant–fatty acid material in a Hele-Shaw cell

Abstract

We present an experimental study of pattern formation during the penetration of an aqueous surfactant solution into a liquid fatty acid in a Hele-Shaw cell. When a solution of the cationic surfactant cetylpyridinium chloride is injected into oleic acid, a wide variety of fingering patterns are observed as a function of surfactant concentration and flow rate, which are strikingly different than the classic Saffman-Taylor (ST) instability. We observe evidence of interfacial material forming between the two liquids, causing these instabilities. Moreover, the number of fingers decreases with increasing flow rate Q, while the average finger width increases with Q, both trends opposite to the ST case. Bulk rheology on related mixtures indicates a gel-like state. Comparison of experiments using other oils indicates the importance of pH and the carboxylic head group in the formation of the surfactant-fatty acid material.

Rapid Stabilization of Immiscible Fluids using Nanostructured Interfaces via Surfactant Association

“…Aqueous surfactant solutions containing spherical micelles have been previously shown to develop various interfacial instabilities when the micelles come into contact with a second solution such as NaSal solution or fatty acid [48][49][50]. Here, we show that similar interfacial instabilities form when a CPCl solution is injected into OA.…”

“…However, research on dynamic phenomena in which structural self-assembly stabilizes the interface under nonequilibrium conditions is still in its infancy. This is despite the fact that in situ self-association of amphiphilic molecules has been widely observed for a variety of practical or industrial applications including oil recovery [45][46][47], flow instabilities [20,[48][49][50][51], biological systems [52][53][54], and rare metal extraction [55]. There has yet to be a fundamental study on dynamics of interfacial material formation between associating surfactants at immiscible liquid interfaces, and the connection between structure and property relationships, in addition to the underlying mechanism of structure development at the molecular level.…”

Chemo-Hydrodynamic Patterns and Instabilities

“…This instability has been thoroughly studied both experimentally and theoretically because, among others, of its ubiquity in oil recovery when a fluid like water or CO2 displaces the more viscous oil in the soils (Saffman & Taylor (1958), Homsy (1987)). In this context, reactions producing for instance surfactants in situ can modify the local surface tension and affect the Safmann-Taylor instability between two immiscible fluids (Jahoda & Hornof (2000), Nasr-El-Din et al (1990), Hornof & Baig (1995), Fernandez & Homsy (2003), Niroobakhsh et al (2017), Tsuzuki et al (2019)). We won't review this particular case as we focus here on miscible systems.…”

Impact of surfactant addition on non-Newtonian fluid behavior during viscous fingering in Hele-Shaw cell

“…When the flow rate increases, the interface becomes more unstable and the number of fingers increases. The fingers become narrower and side-branching occurs 3,4,5,8,14,20 .…”

“…Recently Tsuzuki et al 19 proposed an alternative explanation and suggested that surfactant advection could be enhanced by a combination of fountain flow and Marangoni effect 46 . Niroobakhsh et al 20,21 investigated the injection of cationic surfactant solution into oleic acid and included the interfacially forming material as a cause of the viscous instabilities.…”