NMR methods and devices for the characterization of flows and transfers in milli-channels

International audienceMilli-fluidics is the technology of flows in channels with characteristic dimensions of a few hundred microns. At this scale, capillary and viscosity effects are more important than volume forces and diffusion is often dominant over advection. The flows through milli-fluidic systems are implemented in several domains such as synthesis chemistry, biology and process engineering. The study of phenomena in milli-fluidic devices faces two major problems. One is that microfabrication techniques require costly investments and a good technological knowledge. Second, the geometric complexity of the systems induces difficulties due to optical access.NMR/MRI methods are adapted to the study of such complex systems, provided that a specific instrumentation is developed in order to improve the sensibility of the measurement. In this context, our study aims to implement, with a low-cost methodology, specific devices to study flows and transfer phenomena in milli-fluidic systems and to optimize NMR/MRI methods for their characterization.Two applications have been developed. The first one consists in a study of the growth of a biofilm in a capillary of submillimeter dimensions and the characterization of the hydrodynamics of the flow in presence of this biofilm. The second one is the study of the flow regime and hydrodynamic instabilities occurring in micromixers. For each application, a specific device was set up, including the milli-fluidic system and the radio frequency (RF) coil adapted to the geometry and dimensions of the system. The milli-coils were fabricated by etching on flexible copper/Kapton® substrates. With the considered geometrical parameters, the RF simulations showed that the milli-coils produce an intense and homogeneous field and the MRI measurements demonstrate an improvement in signal to noise ratio of a factor about 7 to 10 compared to the commercial MicWB40 probe which allows the detailed analysis of the above-mentioned phenomena in the context of milli-fluidic applications