Control of emulsion drop production in flow focusing microfluidics

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Title: Control of emulsion drop production in flow focusing microfluidics
Author: Kim, Haejune
Abstract: Generating droplets using flow -focusing microfluidics in multiphase flows has reached its limit that it cannot generate submicrometer droplets in size . Flow focusing geometry together with an electric field has been used to make smaller droplets in microchannels . The droplet size was controllable by the flow rate ratio as well as the electric field . The droplets size decreased as the voltage increased . A Taylor cone was formed to generate very fine droplets which were less than 1m ? in diameter . The tip made smaller droplets due to the tangential force by the electric field . A small inner flow rate and high electric field were required to form a stable Taylor cone in a DC electric field . The droplet size , however , was not stable at a small water flow rate because the flow rate was not as accuate as required . When I used a modified syringe pump with more accurate flow rate control , I was able to obtain a stable set of data . A small change in droplet size occurred at low voltage . The drop size changed dramatically , when the voltage was high enough . I also observed how an AC electric field affects the droplet size . The droplet size was not solely determined by the voltage . This is because of the imbalance of the supplied flow rate and the emitted flow rate . I also found that the droplet size is related to the tip position of the dispersed phase . The droplet size decreased as the tip stretched more . Typically , the microfluidic device generated monodispese droplets in narrow size distribution . It also generated a bigger droplet followed by a smaller one consecutively at low flow rate ratio of inner and outer fluid flow ( )265 .0 /09 .0 ? ?oiQQ . To understand this instability of drop formation , a numerical calculation was conducted . The simulation results showed inside of the tip still pointed downstream after it generated a big droplet . Then , the tip generated another smaller droplet while the tip was stretched . Finally , the tip moved back and began a new cycle .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1563
Date: 2009-05-15


Control of emulsion drop production in flow focusing microfluidics. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1563 .

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