Impact of inlet channel geometry on microfluidic drop formation
Wiki entry by : Dongwoo Lee, AP225 Fall 2010.
Paper in this Wiki : A. R. Abate, A. Poitzsch, Y. Hwang, J. Lee, J. Czerwinska, and D. A. Weitz, Impact of inlet channel geometry on microfluidic drop formation, PHYSICAL REVIEW E 80, 026310 (2009)
The paper illustrates the impact of inlet channel geometry on microfluidic drop formation. With some experiments, it was found that in TJ and PJFF drop formation, the asymmetric injection of fluids leads to a stable drop formation at low capillary numbers, while monodisperse drop formation was made at high capillary numbers in FF drop formation as shown in the Fig. 1. In the experiment, the emulsions formed consist of water drops in fluorocarbon oil stabilized by fluorosurfactant. Figure 2 shows more quantitative comparison of the capillary effect on the drops for different geometries. In the Figure, the authors include the stable drops only. Thus, we can clearly see the geometry and the capillary number effects on the stability of the drops. One interesting characteristic we can see in the plot is that as capillary number is increased, drop size is reduced. This is because shear stress in the nozzle increases. Fig. 3 shows the full phase space for stable drop formation for different channel geometries. Generally, the PJFF drop maker has a large region of stable drop formation as in the Fig. 3(b) In FF2 drop maker, smaller stable drop formation region exists. However, the authors says that FF drop makers form monodisperse drops most rapidly, useful for applications that require large quantities of drops.
Soft Matter Discussion
This paper describes the effect of channel geometry and the capillary number on the stability and shape of drop formation. Given the fact that larger capillary number means larger viscosity effect compared with surface tension effect, one can expect that larger capillary number makes the drop smaller. This general pattern was shown in the result of the paper. (Fig. 1.) However, above or below threshold, the drops lost their stability and this effect is due to the shape of the channel. Since each type of channel geometry has its own advantages (eg. PJFF : larger stability region, FF2: faster drop formation and stable region where PJFF cannot covers), this research is valuable for designing micro fuluidc channels which controls the stability or the size of drops. Further research can be done for figuring out the exact effect of the channel geometry on drop formation to find out the optimized shape and size of the channel to control drop formation.