The paper by Shelley L. Anna, Nathalie Bontoux, and Howard A. Stone from Harvard University explores the formation of dispersions using flow focusing in microchannels. The authors integrate a flow-focusing geometry into a microfluidic device to study drop formation in liquid-liquid systems. They observe two regimes: one where drop size is comparable to the orifice width, and another where drop size is dictated by the diameter of a thin "focused" thread, allowing for the formation of much smaller drops than the orifice. Both monodisperse and polydisperse emulsions can be produced by varying the flow rates of the two liquids. The study highlights the potential of this method for precise control over droplet size and distribution, which is useful in various applications such as personal care products, food, and drug delivery. The authors also discuss the fabrication methods and experimental setup used to achieve these results, emphasizing the importance of surfactants in stabilizing droplets and addressing wetting issues in small devices.The paper by Shelley L. Anna, Nathalie Bontoux, and Howard A. Stone from Harvard University explores the formation of dispersions using flow focusing in microchannels. The authors integrate a flow-focusing geometry into a microfluidic device to study drop formation in liquid-liquid systems. They observe two regimes: one where drop size is comparable to the orifice width, and another where drop size is dictated by the diameter of a thin "focused" thread, allowing for the formation of much smaller drops than the orifice. Both monodisperse and polydisperse emulsions can be produced by varying the flow rates of the two liquids. The study highlights the potential of this method for precise control over droplet size and distribution, which is useful in various applications such as personal care products, food, and drug delivery. The authors also discuss the fabrication methods and experimental setup used to achieve these results, emphasizing the importance of surfactants in stabilizing droplets and addressing wetting issues in small devices.