In this paper, we report a new and simple method for manipulating free droplets using ferrofluid dynamics. For the movement of free droplets using ferrofluid, a periodic pattern of ferrofluid is generated by using a strip magnet and dynamically modified using a magnetic stirrer. The dependence of droplet movement on the size of droplets and the rotation speed of the magnetic stirrer is studied. In order to improve the mixing efficiency, a discontinuity in the ferrofluid pattern at the mixing spots is created by adding a smaller strip magnet to the above setup. We demonstrate a reduction in the mixing time at the target spot as compared to the setup without the addition of the smaller strip magnet. A novel aspect of the reported work is the use of ferrofluid dynamics to control the movement and mixing of free microdroplets without sample evaporation and solid surface contact contamination.
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