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Dr. Ignacio Pagonabarraga
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Lattice-Boltzmann simulation of complex fluids
The study of the dynamics of suspensions containing mesoscopic particles (colloids, polymers, surfactants, proteins, etc.) poses a number of fundamental problems, because it is necessary to describe the dynamics both of the solvent and of the suspended objects. Since their sizes differ orders of magnitude, also the time scales in which they evolve will differ similarly.One of the possible ways to tackle the problem is to approximate the dynamic description of the solvent, in such a way that we do not need to follow it in its microscopic details. In this school several strategies to perform such a task in a consistent way will be discussed.
In this set of lecture I will concentrate in lattice-Boltzmann, a simulation technique that has been developed during the previous decades and it is by now a well established method to deal with complex fluids in complex geometries. Although initially introduced to study high Reynolds fluid dynamics, it has been in its application to porous media and soft matter where it has shown its major capabilities.
I will describe the basics of the method, showing how the collective dynamics of the solvent is recovered, which provides a sound procedure to account for the collective dynamics of the solvent. I will concentrate on the application of lattice-Boltzmann to binary mixtures (and in general to other complex fluids). I will also consider how boundaries are incorporated, both as real solid walls, or by implementing Lees-Edwards boundary conditions. In the case of mixtures, it is also important to account for wetting behavior when the fluid is in contact with the solid wall. In some cases it is important to keep track of the positions of the solute. I will analyze this situation in detail for the particular case of colloidal dynamics, where it is necessary to combine lattice-Boltzmann with MD-like algorithms. I will also describe a recent approach to account for polymer dynamics within lattice-Boltzmann. Along the previous discussions I will try to emphasize how this method compares with other techniques, pointing out its potentiality and also its weaknesses.