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Emulsions stabilization using electrokinetics

Monday, June 13, 2016 2:00 PM;

JGU Mainz, Physics, Newton-Raum

Speaker: Julien Lombard; University of Barcelona

Binary fluids, composed of two immiscible solvents, are relevant in many processes in nature, biology as well as in industrial applications dealing e.g. with oil extraction, food production or drug formulation1. When initially mixed, these fluids tend to form domains where one of the phases is predominant. The ability to understand the formation of these domains and more importantly to control and tune their shape and their stability is of high importance.

Recently, the generation of droplets of submicronic size has attracted a lot of interest, resulting in the emergence of the new research field of nanoemulsions. Those emulsions display specific properties, among which for example, an increased effectiveness when used for drug delivery. However, unlike their submicronic size counterparts, those nanodroplets are not thermodynamically but only kinetically stable. There is therefore a need to understand and develop new ways of producing stable nanoemulsions.

In this talk, we will present new numerical results regarding the stabilization of nanoemulsions through the addition of ions in the binary fluid solution. Indeed, the size of the droplets being comparable to the length scales (typically the Debye length2) over which dissolved ions partition at their interface, electrokinetics effects can play a role in the way a binary fluid demixes and in the structure of the resulting emulsions by introducing a repulsive force between the charged droplets (an effect already observed in the case of charged colloids3).

We will first present the numerical approach we use through the program Ludwig4, which aims at simulating the behavior of complex fluids in 3D. This program based on the Lattice-Boltzmann model (LB) simulates the Boltzmann equation with linearized collisions on a lattice, which allows for a mesoscopic description5 of the system, accounting for interfacial effects such as ionic distribution. The particular case of binary fluid is considered via an order parameter φ in a diffuse interface-like description.

In a second part, we will give an overview of the results we obtained so far concerning the stabilization of emulsions and the parameters controlling the fluid demixing.

Finally, we will show how the ionic distribution across a 1D fluid/fluid interface can lead to various electro-osmotic profiles and streaming currents depending on the properties of the fluid.

[1] C. Holtze, J. Phys. D: Appl. Phys. 46, 114008 (2013).
[2] L. Bocquet and E. Charlaix, Chem. Soc. Rev. 39, 10731095 (2009).
[3] M. E. Leunissen, A. van Blaaderen, A. D. Hollingsworth, M. T. Sullivan and P. M. Chaikin, PNAS 104, 2585-2590 (2007).
[4] Jean-Christophe Desplat, Ignacio Pagonabarraga and Peter Bladon, Computer Physics Communications 134 273–290 (2001).
[5] B. Rotenberg, I. Pagonabarraga and D. Frenkel, Faraday Discussions 144, 223 (2010).


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