A Continuous Approach to the Dynamics of Out of Equilibrium Systems

We developed miniaturized fluidic tools for chemistry and physical chemistry. After 4 years of development, we eventually focused on a reduced set of micro and millifluidic techniques for which we possess the technological expertise and a real understanding of their working behaviour. These tools are unique in the degree of control they yield in the manipulation of fluids on the nL to µL scale. We now plan to use them in focused cases with no major development but rather continuing . The core of our work is based on digital microfluidics where nL-sized drops are used as reactors. With a Chemical Engineering approach, we gave a fine description the inner hydrodynamics and the mixing process of multicomponents drops. We focussed on relevant parameters such as the degree of confinement, the channel geometries, the role of inner and outer viscosities, etc. to yield a neat description and a chart for choosing the size of the reactor in terms of kinetics, thermal exchange, mixing time. It turns out that ultra small sizes are not always relevant to industrial chemistry. By scaling up to the millimeter our devices, we actually developed ultra-fast prototyping tools not only for the sake of fluidics itself but also for Analytical chemistry. Combining the two technologies (precise microfluidics + astute millifluidics) in an environment with a high degree of automation (sensors, actuators, computing control) yields devices that offer the facile manipulation of trains of drops and their history, namely mixing, dilution, chemical reaction, thermal quench, etc. Those tools have been used intensively for the rapid and continuous production of either objects or data with i) creation in millifluidic devices of sophisticated and fine colloidal material and ii) phase diagram studies of solutions with full characterization (e.g. measurement of solubility, nucleation rate, polymorphism, etc.). The tools are now used on an industrial basis for instance for the screening of catalysts. Beside droplet-based studies, we also developed two significant microfluidic strategies for continuously probing the change of state for instance in a mixture of several components: interdiffusion and microevaporation. The former concerns the laminar case of coflowing streams of different yet miscible liquids which we fully describe experimentally and theoretically, while microevaporation exploits the confined and controlled evaporation of a solvent to concentrate a solution on the nanoliter scale and to probe it along a kinetics pathway toward high concentrations.