Splitting behavior of Janus drop impact on protrusion structure

Abstract

Handling tiny liquid volumes as drops is important for applications, including biochip or liquid spraying systems. Splitting of a compound drop is a challenging task in the industrial fields, but the underlying mechanism is not clearly revealed. Here, we demonstrate the dynamic characteristics of the bounce and separation of Janus drops on protrusions by using a numerical method. A regime map for the separation rate between low- and high-viscosity components is investigated for various viscosity ratios and Weber numbers, which is discussed in terms of the formation of a ring and the reduction in residence time. We predict off-centered drop impact on the protrusion structure under various offset distances and characterize the impact behavior into the ring and bifurcation bouncing. We investigate how the separation rate is affected by the protrusion's height and width. The rim dynamics occurring when a liquid film is punctured are discussed by quantifying the evolutions of the shapes and axial momenta of the drops. We expect that the splitting of the compound drop on a defect can create possibilities for the efficient control of drop manipulation and fluid purification.