Physics of Micro- and Nanofluids

9 - 20 June 2008

Venue: Lorentz Center@Oort

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The properties of fluids dynamics in extremely small systems and in the proximity of interfaces has been raised from the very beginning of hydrodynamics, but still occupy a very important place in contemporary science and technology. One may cite many examples: impact problems, e.g. liquid droplets on solid surfaces or bluff bodies on liquid surfaces, with many applications from fertilizer spreading in agriculture to motion of torpedoes for military purposes; drag reducting effects by polymers and bubbles, whose origin is still much debated; miniaturizing fluidic systems to develop lab-on-a-chip (and where the enhancement of viscous damping at micrometric scales makes it necessary to look for new solutions for fluid manipulation); fluid dynamics in biological systems and the understanding of locomotion at small Reynolds number; nanorheology, for example lubrication flows, or flows in nanopores and around nanotubes. Over the last decade, the development of new techniques, both at the experimental and computational level, have allowed to gain much insight into the dynamics at the different scale involved: nanohydrodynamics, dynamical surface force apparatus and atomic force microscopy, particle image velocimetry at the micron scale, high speed video imaging, but also molecular dynamics simulations, continuum like approaches (e.g. Lattice Boltzmann or phase field techniques) and the recent efforts to develop multiscale approaches for the simulations of flows, etc.  Many questions remain however open and the understanding of the interplay of the dynamics at the different scales involved remains to be investigated and understood.  At the lowest microscopic level, surface properties result from the complex interplay of many physical and chemical ingredients: roughness, affinity to the fluid or vapor, surface charges (resulting from dissociation), surfactant adsorption, etc.  At a more macroscopic scale, the influence of these ingredients on the interface properties should be rationalized using established surface concepts like wetting, hydrodynamics boundary condition or surface (e.g. Marangoni) stresses.  Yet, from a dynamical point of view, very little is known concerning the mutual influence of these ingredients on the interface dynamics, nor its potential consequence on the flow pattern at much larger, macroscopic scales. We would like to acquire knowledge from the simplest but representative systems, in order to be able to put this expertise in the development of complex devices. Some questions, particularly in the context of micro and nanoflows, have already been posed, here we would like to better rationalize them, in such a way to ease the approach to these problem. At present there are several experimental challenges, which may strongly impact on the field, and progresses in these directions will be reported and discussed during the workshop. We would like to bring together experimentalists, computer scientists, and theoreticians to disentangle the many effects that are intrinsically connected at the various scales.  The focus of the workshop will be on the physical aspects related to the above mentioned problematics.  One important point will be to gather scientist with different domain of specialization in fluid dynamics, biophysics, chemistry, and micro- and nano-fabrication, in order to share their experience and give the opportunity to induce exchanges between these different communities.

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