We describe continuous flow liquid-liquid phase separation in microfluidic devices based on capillary forces and selective wetting surfaces. Effective liquid-liquid phase separation is achieved by using a thin porous fluoropolymer membrane that selectively wets non-aqueous solvents, has average pore sizes in the 0.1-1 microm range, and has a high pore density for high separation throughput. Pressure drops throughout the microfluidic network are modelled and operating regimes for the membrane phase separator are determined based on hydrodynamic pressure drops and capillary forces. A microfluidic extraction device integrating mixing and phase separation is realized by using silicon micromachining. Modeling of the phase separator establishes the operating limits. The device is capable of completely separating several organic-aqueous and fluorous-aqueous liquid-liquid systems, even with high fractions of partially miscible compounds. In each case, extraction is equivalent to one equilibrium extraction stage.
All for one and one for all: A continuous‐flow, multistep microchemical synthesis of carbamates starting from aqueous azide and organic azoyl chloride by using the Curtius rearrangement reaction is described. The procedure involves three reaction steps and two separation steps (one gas–liquid and one liquid–liquid). Formation of a microreactor network for parallel synthesis of analogous compounds is also demonstrated.
Continuous-flow dielectrophoretic (DEP) particle separation based on size is demonstrated in a microfluidic device. Polystyrene microspheres suspended in a neutrally buoyant aqueous solution are used as model particles to study DEP induced by an array of slanted, planar, interdigitated electrodes inside of a soft-lithography microchannel. The E-field gradients from the slanted electrodes impart a net transverse force component on the particles that causes them to "ratchet" across the channel. Over the length of the device, larger particles are deflected more than smaller particles according to the balance of hydrodynamic drag and DEP forces. Consequently, a flow-focused particle suspension containing different-sized particles is fractionated as the beads flow and separate down the length of the device. The flow behavior of spherical particles is modeled, and the total transverse particle displacement in the microfluidic device predicts fourth-order size and voltage and second-order inverse flow rate dependences. The model is verified experimentally for a range of flow rates, particle sizes, and E-field strengths.
Einer für alle, alle für einen: Eine mehrstufige mikrochemische Durchflusssynthese von Carbamaten aus wässrigem Azid und einem organischen Azoylchlorid mithilfe der Curtius‐Umlagerung wird beschrieben. Der Prozess umfasst drei Reaktionsstufen und zwei Trennschritte (eine Gas‐flüssig‐ und eine Flüssig‐flüssig‐Trennung). Ein Mikroreaktornetzwerk für die Parallelsynthese analoger Verbindungen wird ebenfalls vorgestellt.
Continuous microfluidic liquid-liquid extraction is realized in a microfluidic device by generating emulsions with large interfacial areas for mass transfer, and subsequently breaking these emulsions using electric fields into easily separated segments of immiscible liquids (plugs). The microfluidic device employs insulated electrodes in a potassium hydroxide-etched channel to create large electric fields (100 kV m(-1)) that drive coalescence of the emulsion phase. The result is a transition from disperse to slug flow that can then readily be separated by gravity. Extractions of phenol and p-nitrophenol from an aqueous to hexane-surfactant solution serve as model systems. In addition to the increased surface area in the emulsion, extraction efficiency is enhanced by reverse micelles resulting from the presence of surfactants. The surfactant concentration is varied approximately 1-10 wt% and a general two-parameter model is developed to quantify the extraction behavior and demonstrate the effectiveness of reverse micelle enhanced extraction.
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