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Team:TU Eindhoven/Microfluidics/Results
From 2014.igem.org
Results Droplet Device
Before the droplets were formed, the injected fluids had to be stabilized and had to be controlled until both the oil and water phase are at the flow-focusing cross junction. If this is not done there will be air trapped inside the device, which will lead to incorrect droplet formation.
If the flow rate of the oil phase is too high in comparison with the water phase, the oil phase will enter the water inlet. This also occurs vice versa. So it was necessary to test different flow rates of both the water and oil phase. Due to the viscosity of the fluids and the resistance of the walls of the channels, the injection speed of the fluids was not always the same but most of the time it was equivalent. Also if the droplet forming was stable with a constant flow of the oil and water phase, the size of the droplets could be changed by alternating the speed of the oil phase. When the droplets were formed, it was possible to measure the size and the frequency of the droplets.
Polyacrylamide Droplets
First tests were performed to form polyacrylamide droplets. The continuous phase consists of a solution of N,N'-methylenebisacrylamide (bisacrylamide), acrylamide monomers and ammonium persulfate. (see Oil and Water Phase for more details). The oil phase contains N,N,N',N'-tetramethylethylenediamine (TEMED) and a surfactant in HFE-7500. The surfactant prevents coalescence of the droplets and makes them more stable. TEMED will diffuse to the continuous phase inside the droplets because of its better solubility in water. It acts as a catalyst activating ammonium persulfate by forming free radicals. These free radicals in turn interact with the acrylamide monomers and the bisacrylamide which also turn into free radicals. This mechanism continues until a network of polyacrylamide is formed with random cross-linkers of bisacrylamide in between.
A flow ratio oil:water of 13:1 µl/min was used to obtain droplets as seen in figure 1. A histogram (Figure 2) of another test showed the mean size of the droplets was 18 µm.
