The development and operation of a modified method for the preparation of quasi-monodisperse (CV < 16%) emulsions are reported. The device uses a microfabricated-nozzle (MN) array, produced by micromachining technology, to achieve a higher rate of emulsification [76.8 m 3 /(m 2 ·h)] than previously reported for microchannel (MC) emulsification methods. The dispersed phase is extruded into a continuous phase through the MN, and the emulsion droplets are formed by viscous drag force of the continuous phase. The droplet diameter decreased with an increase in the flow velocity and viscosity in the continuous phase, which was explained by the theoretical model. The range of droplet diameters produced (130 to 370 µm) was larger than in previously reported MC emulsification, membrane emulsification, and shear-rupturing methods.Paper no. J10940 in JAOCS 82, 73-78 (January 2005).Emulsions have been widely used in various industries, including foods, cosmetics, and pharmaceuticals. Many of the most important properties of emulsion-based products (e.g., shelf life, appearance, texture, and flavor) are determined by the size of the droplets they contain (1). Emulsions are conventionally prepared by using colloid mills, rotor-stator systems, and highpressure homogenizers. Emulsions produced by these methods are polydisperse and require high energy input (2). Several methods have been developed for preparing quasimonodisperse emulsions. Nakashima et al.(3) developed a membrane-emulsification process for producing monodisperse emulsions (CV of 10-20%). This technique is applicable to both oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions (4,5). The emulsion droplet size is controlled by the size of the membrane pore (3), the dispersed-phase flux, and the continuous-phase flux (6-11). The rate of emulsion formation is determined by the flux of the dispersed phase. In membrane emulsification, the maximum flux of the dispersed phase for an emulsion containing 25% volume fraction is 3.55 m 3 /(m 2 ·h) (4). A different method has been proposed to produce quasi-monodisperse emulsions by shear rupturing in Couette flow (12)(13)(14). In this method, quasi-monodisperse emulsions are produced through droplet rupturing in viscoelastic fluids. The rate of emulsion production for this technique is 1 to 2 L/h for an emulsion containing 70 to 85% volume fraction of oil phase (14).Recently, we proposed a novel method for making monodisperse emulsion droplets from a microfabricated channel (MC) array (15), i.e., MC emulsification. Emulsions with a CV of 5% (16) and droplet sizes of 3 to 100 µm (17,18) have been prepared successfully using this technique. As the driving force for droplet formation, MC emulsification exploits interfacial tension, the dominating force on a micrometer scale. During droplet formation, the distorted dispersed phase is spontaneously transformed into spherical droplets by interfacial tension (16). Droplet formation by spontaneous transformation at a high production rate is difficult, since in theory there i...
