Quantitative Analysis of the Volume Difference of Microdroplets in Vertical Contact Control

We can control the concentration of chemicals in microdroplets by using vertical contact control of droplets. When a microdroplet contacts an opposite microdroplet, chemicals diffuse between the droplets. Then, the coalescent droplet is separated into two microdroplets. Contact control is attractive for use in biochemical applications because it realizes three-dimensional microfluidic systems. However, in vertical contact control, gravity causes a volume difference of the microdroplets, AV, after separation. To solve the problem of gravity, we analyze AV quantitatively. In experiments, we measure the relationship between AV and the size of microdroplets, R. As a result, we find that AV increases proportionally to R5, which agrees with a simple theoretical model based on the balance between gravity and surface tension. Our model suggests that AV of the microdroplets after vertical contact control can be predicted quantitatively with the material parameters of the density and surface tension of the liquid.

Automated summary

Vertical contact control can manipulate the concentration of chemicals in microdroplets and achieve three-dimensional microfluidic systems. Experimental results show that the volume difference of microdroplets, AV, increases proportionally to the fifth power of the size of microdroplets, R, which can be predicted quantitatively with material parameters such as density and surface tension.