(164d) Thermo-Hydrodynamic Behavior of Coflowing Fluids in Microfluidic Supercritical Antisolvent Processes

Supercritical antisolvent techniques have demonstrated promises for processing organic materials at the nanoscale. However, their industrial development is still limited by the poor understanding of the inherent coupled physico-chemical mechanisms (thermodynamics, hydrodynamics, and nucleation-growth). To address the classical limitations, it is necessary to considered microscale approaches for which the experimental conditions are well controlled and can be more easily modelled at the micrometer scale by numerical approaches in order to catch the physical phenomenon (mixing, diffusion) occurring at the smallest scales (Bachelor, Kolmogorov).

Previous work have demonstrated that it was possible to obtain implement Supercrical AntiSolvent processes in microfluidics devices (µSAS), but without deeper investigations into the physico-chemical phenomena. Indeed, micromixing could have a significant effect over particles size and size distribution since homogeneous concentration distribution and high degree of supersaturation can only be reached by intense micromixing obtained through various strategies of mixing geometries.Therefore, we have investigated coflowing fluids at high pressure, which are largely used in various supercritical fluids processes including emulsion generation or antisolvent. By observing fluid flow behavior in coflow microfluidic devices, both immiscible and miscible mixtures were tested and the obtained results will be presented in this talk.

In the particular case of miscible fluids conditions (CO₂ and ethanol), thermodynamics plays an important role over hydrodynamic behavior. Depending on the considered conditions (p, T, X_EtOH) and the location within the EtOH-CO₂ phase diagram, several different behaviors can be observed. For monophasic mixtures (liquid or supercritical), no obvious interface could be noticed, meaning the mixture velocity plays an essential role to characterize the fluid behavior. By applying a micro Particle Imaging Velocimetry (µPIV) techniques inside microfluidic systems, to a mixture of ethanol and CO₂ - at SAS conditions - fluid mixture velocity field is obtained and compared with numerical simulation in order to provide interesting data including the micromixing time.