The precision manipulation of streams of fluids with microfluidic devices is revolutionizing many fluid-based technologies and enabling the development of high-throughput reactors that use minute quantities of reagents. However, as the scale of these reactors shrinks, contamination effects due to surface adsorption and diffusion limit the smallest quantities that can be used. The confinement of reagents in droplets in an immiscible carrier fluid overcomes these limitations, but demands new fluid-handling technology. We present a platform technology based on charged droplets and electric fields that enables electrically addressable droplet generation, highly efficient droplet coalescence, precision droplet breaking and recharging, and controllable droplet sorting. This is an essential enabling technology for a high-throughput droplet microfluidic reactor.Networks of small channels are a flexible platform for the precision manipulation of small amounts of fluids. [1,2] The utility of such microfluidic devices depends critically on enabling technologies such as the microfluidic peristaltic pump, [3] electrokinetic pumping, [4,5] and dielectrophoreticpump or electrowetting-driven [6] flow; these technologies can form the essential building blocks for the assembly of fluidhandling modules.[7] These modules can be used to perform a variety of key tasks including the measurement of precise aliquots of fluids, the combination of fluid streams, and the mixing of multiple fluid components. The assembly of such modules into complete systems provides a convenient and robust way to construct microfluidic devices. These have myriad uses; for example, high-throughput screening, [8] the exploration of chemical phase diagrams, assays of biological molecules, [9][10][11] single-cell analysis, [12][13][14][15][16][17] and combinatorial approaches to protein crystallization [18] can all be performed with only minimal consumption of reagents. However, virtually all microfluidic devices are based on flows of streams of fluids; this sets a limit on the smallest volume of reagent that can be used effectively because of the contaminating effects of diffusion and surface adsorption. As the dimensions of small volumes are decreased, diffusion becomes the dominant mechanism for mixing leading to dispersion of reactants. Moreover, surface adsorption of reactants, although small, can be highly detrimental at low concentrations and small volumes. As a result current microfluidic technologies cannot be reliably used for applications involving minute quantities of reagent-for example, bioassays at levels down to the single molecule are not easily performed. An approach that overcomes these limitations is the use of aqueous droplets in an immiscible carrier fluid; [19] these droplets provide a well-defined, encapsulated microenvironment that eliminates cross-contamination or changes in concentration caused by diffusion or surface interactions. Droplets provide the ideal microcapsule that can isolate reactive materials, cells, or small particles f...

A microfluidic device denoted the Phase Chip has been designed to measure and manipulate the phase diagram of multi-component fluid mixtures. The Phase Chip exploits the permeation of water through poly(dimethylsiloxane) (PDMS) in order to controllably vary the concentration of solutes in aqueous nanoliter volume microdrops stored in wells. The permeation of water in the Phase Chip is modeled using the diffusion equation and good agreement between experiment and theory is obtained. The Phase Chip operates by first creating drops of the water/solute mixture whose composition varies sequentially. Next, drops are transported down channels and guided into storage wells using surface tension forces. Finally, the solute concentration of each stored drop is simultaneously varied and measured. Two applications of the Phase Chip are presented. First, the phase diagram of a polymer/salt mixture is measured on-chip and validated off-chip and second, protein crystallization rates are enhanced through the manipulation of the kinetics of nucleation and growth. Keywords microfluidics; PDMS; water permeation; high throughput protein crystallization; phase diagram; nucleation; growth; Ostwald ripening Microfluidic instruments are capable of precisely manipulating sub-nanoliter quantities of fluids. Their purpose is to vastly reduce the amount of fluids used in chemical processing and provide accurate delivery of fluids in a defined geometry on the micron length scale with a temporal accuracy of milliseconds. A microfluidic device can include channels for transporting fluids, valves for controlling flow, nozzles to create drops, pumps to propel fluids, storage chambers, and mixers to homogenize multiple fluid streams and drops 1-4 . To this panoply of components we add the abilities to store drops and to controllably vary the water content of stored drops. Each of these primitive functions can be combined in numerous ways to create complex devices optimized for specific tasks. Other powerful features of microfluidics are the ease and rapidity of their construction and the low cost of materials. This paper reports the development of a microfluidic device, the Phase Chip shown in Figure 1a, which is designed to determine the phase diagram of multi-component fluid mixtures. The

Diblock copolymers are known to spontaneously organize into polymer vesicles. Typically, this is achieved through the techniques of film rehydration or electroformation. We present a new method for generating polymer vesicles from double emulsions. We generate precision water-in-oil-in-water double emulsions from the breakup of concentric fluid streams; the hydrophobic fluid is a volatile mixture of organic solvent that contains dissolved diblock copolymers. We collect the double emulsions and slowly evaporate the organic solvent, which ultimately directs the self-assembly of the dissolved diblock copolymers into vesicular structures. Independent control over all three fluid streams enables precision assembly of polymer vesicles and provides for highly efficient encapsulation of active ingredients within the polymerosomes. We also use double emulsions with several internal drops to form new polymerosome structures.