Modeling of droplet traffic in interconnected microfluidic ladder devices.

The problem of controlling the droplet motion in multiphase flows on the microscale has gained increasing attention because the droplet-based microfluidic devices provide great potentials for chemical and biological applications. It is critical to understand the relevant physics on droplet hydrodynamics and thus control the generation, motion, splitting, and coalescence of droplets in complex microfluidic networks. Numerical simulations using the volume of fluid algorithm are conducted to investigate the time-dependent dynamics of droplets in gas-liquid multiphase devices. An analytical model based on the electronic-hydraulic analogy is developed to describe the hydrodynamic behavior of the droplets in interconnected microfluidic ladder devices. It is found that the pressure drop caused by the droplets plays a critical role in the droplet synchronization. A fitted formula for pressure drops in the presence of surfactant is achieved by using numerical simulations. Both the numerical and the theoretical results agree well with the corresponding experimental results.