Abstract The chapter offers an introduction to microfabrication techniques. Photolithography is presented. Techniques dedicated to hard materials, such as wet and plasma etching, sputtering, bonding, electron beam lithography. Direct writing and 3D printing are shown. Soft lithography, and in particular those using PDMS (PolyDimethylSiloxane) is presented, with applications to valving, pumping, leading to Large Scale Integration Systems. Paper microfluidics is discussed, along with recent technological approaches, such as photosensitive hydrogels, NOA technology, microcontact printing or flow lithography.

Abstract This concerns the hydrodynamics of microfluidics, in the presence of free interfaces. In particular bubbles an droplets in microchannels. Basics of interfaces are shown, including discussions on capillarity, surface tension Laplace law, wetting. Surfactants, which play a major role in microfluidics, are presented. Various laws are discussed: Washburn law, Landau Levich, Breteherton, Rayleigh Plateau. These notions are used to discuss the behaviour of droplets in microfluidic systems: breakup, coalescence, bubble pressure drop, droplet production.

Abstract This concerns the hydrodynamics of small systems, without free interface, i.e. with rigid boundaries. The foundations of the governing equations are discussed: the notion of fluid particle, introduced by GK Batchelor, the case of nanofluidics and sub-nanofluidics, the mean free path in gases. Then the notion of slippage at walls are presented for the cases of liquids and gases. Sections are devoted to the notions of hydrodynamic resistances and capaticances. Finally, inertial microfluidics, i.e. microfluidics or millifluidics at moderate Reynolds numbers, is presented.

The capacity of microfluidic technology to fabricate monodisperse emulsion droplets is well established. Parallelisation of droplet production is a prerequisite for using such an approach for making high-quality materials for either fundamental or industrial applications where product quantity matters. Here, we investigate the emulsification efficiency of parallelised drop generators based on a flow-focusing geometry when incorporating the role of partial wetting in order to make emulsion droplets with a diameter below 10 μm. Confinement intrinsically encountered in microsystems intensifies the role played by interfaces between liquids and solids. We thus take advantage of partial wetting to enhance the maximum confinement accessible due to liquid flow focusing. We compare the performances brought by partial wetting to more established routes such as step emulsification. We show that the step configuration and the partial wetting regime are both well suited for being parallelised and thus open the way to the production of fine and calibrated emulsions for further applications. Finally, this new route of emulsification that exploits partial wetting between the fluids and the channel walls opens possibilities to the formation of substantially smaller droplets, as required in many fields of application.

Submitted for the MAR06 Meeting of The American Physical Society Playing with Microfluidic Droplets and Actuators PATRICK TABELING, ESPCI-CNRS, VALESSA BARBIER, Univ Paris XIII, HERVÉ WILLAIME, ESPCI-CNRS, MMN TEAM — In the lab-on a chips of the future, flows will be handled at the microscale through mazes of microchannels using actuators. Here we concentrate on PDMS based microfluidic systems and we use actuators to introduce localized perturbations on a chip, close to where droplets are formed, i.e. near the intersection of a main and a side channel along which oil and water flows are driven. We observe Arnold tongues and devil staircases leading to the formation of regular or quasiperiodic-like droplets. These behaviors are well accounted for by modelling the system as a non linear oscillator driven by an external forcing. The characteristics of the regimes that are observed depend on the flow-rate conditions. In some range of flow-rates, we show that the droplet sizes can be varied by one order of magnitude by changing the actuation frequency, without modifying the flow-rates.These findings are used to understand the complex behavior of droplet emittors placed in parallel. Patrick Tabeling ESPCI-CNRS Date submitted: 03 Dec 2005 Electronic form version 1.4

Emulsion activable par ultrasons comprenant, en emulsion dans une solution aqueuse, des microparticules (1) de diametre (D) inferieur a 10 µm comprenant un agent actif et un precurseur gazeux (3) sous forme liquide encapsules par un premier emulsifiant (4). Les microparticules contiennent des nanoparticules (5) de taille inferieure a 1 µm en emulsion dans le precurseur gazeux, chaque nanoparticule comprenant un liquide interne (6) qui contient l’agent actif et qui est encapsule par un deuxieme emulsifiant (7).

We propose a novel approach, based on microfluidic technology, dedicated to the exploration of phase diagrams of binary and ternary aqueous systems. The system consists in concentrating solutions in independent microchambers by pervaporating water through PDMS membranes. On the chip, we implement a novel optical technique that allows to monitor in real time the concentration in each chamber. The approach is applied to binary and ternary mixtures, including salts and surfactant solutions. The system allows to detect the formation of crystals along with measuring supersaturations and the solubility level.