The recent developments of soft lithography and microfluidic techniques now permit the manipulation of small quantities of fluids with very good control and reproducibility. These advances open a new ...“bottom-up” route to emulsification that paves the way to the fabrication of calibrated hierarchically organized emulsions and particles. In this article, we describe the microfluidic techniques elaborated for engineering emulsions and new dispersed materials and discuss their advantages over “top-down” approaches. We review and comment the high potentialities these techniques offer to emulsion and colloid science, to the development of high-throughput set-ups for chemistry, physics and biology. We illustrate them through a few examples taken from the current literature.
We describe a continuous flow scheme to conceive and produce hierarchically organized large emulsions and particles with very good control over size, shape and internal structure. By assembling ...together elementary co-axial flow modules and integrating their corresponding functions, modular set-ups can be designed “on demand” to engineer complex architectures in characteristic sizes ranging from 50
μm up to a few millimeters. The high potentiality of this approach stems from the continuous production of drops and the ability to manipulate and functionalize each one independently “on line”. Its great versatility is limited only by the number of combinations possible using the modular toolbox and one's imagination. We illustrate this through the encapsulation of droplets or solid particles of various shapes, composition and size, in liquid or solidified drops as well as the formation of large organic or inorganic cylindrical particles.
We report that, when a train of confined droplets flowing through a channel reaches a junction, the droplets either are alternately distributed between the different outlets or all collect into the ...shortest one. We argue that this behavior is due to the hydrodynamic feedback of droplets in the different outlets on the selection process occurring at the junction. A "mean field" model, yielding semiquantitative results, offers a first guide to predict droplet traffic in branched networks.
By studying the repartition of monodisperse droplets at a simple T junction, we show that the traffic of discrete fluid systems in microfluidic networks results from two competing mechanisms, whose ...significance is driven by confinement. Traffic is dominated by collisions occurring at the junction for small droplets and by collective hydrodynamic feedback for large ones. For each mechanism, we present simple models in terms of the pertinent dimensionless parameters of the problem.
A high-throughput tubular millifluidic platform for performing slow kinetics measurements occurring in liquid phase, using minute amounts of reactant is described. The method consists of generating ...periodic trains of monodisperse droplets in a capillary tube and using these droplets as micro-reactors. In contrast to microfluidic lab-on chip devices, limited to fast kinetics measurements, this setup permits to extract kinetic rate constants of slow reactions at very low cost without requiring any use of soft lithography or glass etching technique for its design, nor miniaturization of analytical tools. It therefore appears very well suited for laboratories and industrial research and development centers.
The continuous production “on demand” of large polymerized objects is presented using a versatile, easy to implement and low cost “millifluidic” reactor. Over microfluidic devices, the present set-up ...offers two considerable advantages: (i) much larger particles are produced with a very good control of sizes and shapes and (ii) no lithography is required for its design. Considering the high modularity of this synthetic pathway, “tubular millifluidic” appears as a new concept of synthesizing particles with a strong control over final object sizes, monodispersity and aspect ratio. The possibility to reach a high scale production makes it a promising production tools for the industry.
For the first time we have combined sol–gel chemistry and millifluidic to generate silica ceramic engineering their sizes and aspect ratios. The particle sizes are controlled by varying the flow ...rates of the continuous and disperse phases within the home-made millifluidic reactor. Also, the silica particles aspect ratio can be tuned by adjusting the constrained geometry of the millifluidic devices, leading to the production of rod-like silica ceramics. Both SAXS and nitrogen physisorption measurements reveal that final inorganic silica ceramics are essentially microporous.
We present experimental, numerical, and theoretical studies of droplet flows in hydrodynamic networks. Using both millifluidic and microfluidic devices, we study the partitioning of monodisperse ...droplets in an asymmetric loop. In both cases, we show that droplet traffic results from the hydrodynamic feedback due to the presence of droplets in the outlet channels. We develop a recently-introduced phenomenological model W. Engl, Phys. Rev. Lett. 95, 208304 (2005) and successfully confront its predictions to our experimental results. This approach offers a simple way to measure the excess hydrodynamic resistance of a channel filled with droplets. We discuss the traffic behavior and the variations in the corresponding hydrodynamic resistance length L_{d} and of the droplet mobility beta , as a function of droplet interdistance and confinement for channels having circular or rectangular cross sections.
