2 research outputs found
Molecular rotors for in situ local viscosity mapping in microfluidic chips
In numerous industrial processes involving fluids, viscosity is a determinant
factor for reaction rates, flows, drying, mixing, etc. Its importance is even
more determinant for phenomena observed are at the micro- and nano- scales as
in nanopores or in micro and nanochannels for instance. However, despite
notable progresses of the techniques used in microrheology in recent years, the
quantification, mapping and study of viscosity at small scales remains
challenging. Fluorescent molecular rotors are molecules whose fluorescence
properties are sensitive to local viscosity: they thus allow to obtain
viscosity maps by using fluorescence microscopes. While they are well-known as
contrast agents in bioimaging, their use for quantitative measurements remains
scarce. This paper is devoted to the use of such molecules to perform
quantitative, \textit{in situ} and local measurements of viscosity in
heterogeneous microfluidic flows. The technique is first validated in the
well-controlled situation of a microfluidic co-flow, where two streams mix
through transverse diffusion. Then, a more complex situation of mixing in
passive micromixers is considered and mixing efficiency is characterized and
quantified. The methodology developed in this study thus opens a new path for
flow characterization in confined, heterogeneous and complex systems.he
methodology developed in this study thus opens a new path for flow
characterization in confined, heterogeneous micro- and nano- systems
Compressed carbon dioxide as a medium in catalytic hydrogenations: Engineering and chemistry
International audienceIn the frame of designing eco-friendly chemical processes, solvents represent a crucial economic and environmental concern. Compressed carbon dioxide (CO2) is an alternative green solvent for many industrial applications. Herein, we present the most relevant aspects of using compressed CO2 in metal-catalyzed hydrogenation reactions. In the first part, we discuss engineering fundamentals for the description of processes in supercritical fluids, gas-expanded liquids, continuous-flow applications and process design, including safety aspects and examples of heterogeneous catalysis. In the second part, we focus on catalytic systems based on both metal complexes and nano-systems, emphasizing how the catalysts have been adapted to the specificity of CO2. For this purpose, significant aspects such as the catalyst design, the reaction conditions and the use of co-solvents are considered. The main goal of this review is to show the advantages of using this green solvent in catalytic hydrogenations, including a critical analysis concerning its limitations