In this paper, we present a simple method to manipulate free microdroplets using ferrofluid dynamics. First, we use two strip magnets (20 Gauss) to generate a ferrofluid cage-array pattern. Then, a magnetic stirrer (200 Gauss) is placed and rotated underneath them to induce a dynamic change in the pattern. The generated ferrofluid pattern and its dynamics are compared with the simulation results of the magnetic field distribution under various static/dynamic configurations using finite element method (FEM). The mixing effect in individual cells is investigated using silica beads (0.2 μm in size) and a water droplet (40 microliter in volume) first. In order to demonstrate free droplet mixing, two colored water microdroplets (10 microliter in volume) are placed in two separate wells and are driven to move and mix without sample evaporation.

Volume Subject Area:
Fluids Engineering
Topics:
Ferrofluids, Drops, Dynamics (Mechanics), Finite element methods, Water, Evaporation, Magnetic fields, Magnets, Simulation results, Strips, Wells
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