Coalescence of contaminated water drops at an oil/water interface: Influence of micro-particles

Abstract

International audienceThe effect of micro-particles and interface aging on coalescence of millimetre-sized water drops withan oil/water interface is studied over long times. The system is not pure and interface contaminationgrows with time, resulting in a slow but continuous decrease of interfacial tension over time (from 35to 10 mN/m), which is measured in situ using an original technique. Without added micro-particles,coalescence times are randomly distributed and uncorrelated to drop diameter or interfacial tension. Inpresence of 10 !m size hollow glass particles at the oil/water interface, coalescence times become morereproducible and show a clear dependence upon drop diameter and interface aging. Results are consistentwith a classical drainage model assuming that the critical thickness at which interstitial film rupturesscales as the micro-particle diameter, a result that tends to validate the bridging scenario. Interestingly,the film retraction speed during the coalescence process does not follow theoretical predictions in aplanar geometry. High-speed imaging of the retracting film reveals that the hole rim is bending upwardwhile retracting, resulting in a strong slowdown of retraction speed. This is caused by the difference ofinterfacial tension between oil/drop freshly formed interfaces and the aged oil/water interface

Coalescence of Water Drops at an Oil–Water Interface Loaded with Microparticles and Surfactants

“…The physical interpretation of the experimental results is proposed in section 4. The comparison with the results of de Malmazet et al 29 is of crucial importance to unveil the mechanisms involved in the coalescence process. In section 5, the main results and findings of this study are summarized.…”

Drop coalescence in technical liquid/liquid applications: a review on experimental techniques and modeling approaches

“…These investigations were continued by Gillespie and Rideal (1956), Watanabe and Kusui (1958), and Charles and Mason (1960a,b), investigating different oil phases and the influence of surfactants. In the following decades, numerous investigations were published on this topic (Allan et al 1961, MacKay and Mason 1963b, Jeffreys and Hawksley 1965a, Davis and Smith 1976, Dickinson et al 1988, Stevens et al 1990, Kourio et al 1994, Hool et al 1998, Basheva et al 1999, Mohamed-Kassim and Longmire 2004, Aryafar and Kavehpour 2006, Thoroddsen 2006, Ortiz-Duenas et al 2010, Bozzano and Dente 2011, Malmazet et al 2015, where the systematic investigations of Hartland (1967a,b,c) should be emphasized in particular. A review on experimentally determined rest times during the 1950s and 1960s can be found in the work of Vijayan and Ponter (1975).…”

Surfactant effects on the coalescence of a drop in a Hele-Shaw cell

“…With the image acquisition frequency used of 2 kHz only five images could be captured for pure solutions in the first regime compared to approximately 30 for the highest concentrated surfactant solution. Secondly, the pure system is more susceptible to dust present in the cell compared to the surfactant ones (as also reported by [3]), which can affect the final neck expansion velocity. Similar velocity deviations have also been reported by Eri and Okumura [22], where for one set of liquids, neck velocities ranged from 250 to 350 mm/s.…”

“…The film thinning and the coalescence rates depend on the fluid properties and the system conditions. Understanding the dynamics of these two phenomena is important for numerous multiphase applications that involve immiscible liquids and is thus still attracting the interest of many investigators [1][2][3][4][5]. The study of coalescence directly in the complex environment where drops appear (i.e., dispersions, emulsions, and separators) can prove challenging.…”