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We introduce electro-coflow as a way to generate emulsion drops with an average size that can be larger, comparable, and smaller than the smallest geometric feature of the device. The method relies on using three immiscible liquids, two of them having a finite electrical conductivity. There are three regimes of operation that allow the steady generation of drops: dripping, electro-dripping, and an electrically dominated regime. We transit from one to the other by increasing the applied voltage and describe the changes in drop size by balancing the relevant forces in each regime.

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In this work, we present a microfluidics-based microfiber fabrication method with the ability to control both the fiber size and the extent of coiling of the generated fiber. This latter feature allows on-demand generation of both nonwoven and single fiber within the same device, broadening the scope of application of the fabricated fibers. Using a hybrid poly(dimethylsiloxane) (PDMS)-glass microfluidic device, we implement a coflowing solvent removal technique to generate poly(ethylene oxide) (PEO) fibers. Characterization of fibers by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) confirms the production of solvent-free, pure PEO fibers. Control over fiber size using both inner and outer liquid flow rates is demonstrated by scanning electron microscopy (SEM) imaging. More crucially, we employ a complementary flow toward the downstream end of the fiber solidification region to control the extent of coiling of the generated fiber. By simple variation of the complementary flow, we induce a transition from a nonwoven fiber to a single fiber. The presented technique is expected to broaden the scope of microfluidics as a tool for the continuous generation of microfibers with a wider range of applications than the existing microfluidics techniques.