Open Access

ARTICLE

Binary Collisions of Immiscible Liquid Drops for Liquid Encapsulation

Carole Planchette¹, Elise Lorenceau¹, Günter Brenn²

1 Laboratoire de Physique des Matériaux Divisés et des Interfaces, FRE 3300 CNRS, Université Paris-Est, 5 boulevard Descartes, 77454 Marne-la-Vallée cedex 2, France
2 Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology, Inffeldgasse 25/F, 8010 Graz, Austria

Fluid Dynamics & Materials Processing 2011, 7(3), 279-302. https://doi.org/10.3970/fdmp.2011.007.279

Abstract

This work is dedicated to a general description of collisions between two drops of immiscible liquids. Our approach is mainly experimental and allows us to describe the outcomes of such collisions according to a set of relevant parameters. Varying the relative velocity U as well as the impact parameter X we can build for each pair of investigated liquids a nomogram X,U showing three possible regimes: coalescence, head-on separation and off-center separation. In this paper, we also study the influence of the liquid properties, i.e. viscosity, density, surface and interfacial tensions using a set of aqueous glycerol solutions together with a set of silicon and perfluorinated oils. We show that the coalescence regime always leads to full spreading of the oil on the aqueous drop (encapsulation) in contrast to the separation regimes where part of the oil is expelled from the encapsulated drop. For head-on separation, three different mechanisms were identified: reflexive separation, single-reflex separation, and crossing separation. Concerning the stability limits of such collisions, the aqueous phase seems to be of little influence in the range of studied liquids. For off-center collisions, the efficiency of the encapsulation is measured via the amount of oil forming the encapsulating shell. We show that the thickness of this coating can be tuned independently from the liquid properties and drop relative velocity by varying the impact parameter. Finally, we briefly address the case of unequal sized drops and the regimes observed for head-on separation.

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