Advection of droplet collision in centrifugal microfluidics

Centrifugal microfluidics has been developed into a powerful technology in chemistry and biology. Its carrier devices allow us to control flows without external pumps, integrate multiple functions onto a disk, and reduce the consumption of reagents or samples. In centrifugal microfluidics, an artificial gravitational field, which determines the volume forces imposed on the microfluid, can be created by the rotating operation of a disc-like microfluidic chip. Centrifugal microfluidics can be a preponderant approach for droplet manipulation because the dimensionless numbers (e.g., the Reynolds number and the Bond number) of the microflows can be controlled by the reasonable design of such a disc-like chip. To study the advection of droplets in a centrifugal microfluidic chip, this paper presents a numerical investigation for the droplet collisions under different Bond numbers and Reynolds numbers. The progress of the collision advection is simulated by solving laminar flow equations and phase-field equations. The distribution of the mixed droplets is described using particle tracking methods. By evaluating the extending ratio of the interface and the barycenter deviation, it is demonstrated that the Bond number and Reynolds number affect different aspects of the advection. For instance, higher Bond numbers produce larger barycenter deviation and higher Reynolds numbers generate a more chaotic distribution. These simulations reveal the advection of droplet collisions under different Bond numbers and Reynolds numbers. Revealing the effects of these dimensionless numbers and advection mechanism can promote more reasonable design and operation of the centrifugal microfluidic platforms.