Converting Vertical Vibration of a Texture Ratchet into Horizontal Drop Motion

Abstract

A texture ratchet is an anisotropic, periodic, microstructured surface that propels drops when vibrated with a sinusoidal signal at certain frequencies and amplitudes. For each input frequency near the resonant frequency of a drop, there is a threshold amplitude beyond which the drop starts to move. In this thesis, we study the parameters that initiate drop motion and reveal a general relationship between the input frequency and threshold amplitude among drops with different volumes, densities, viscosities and surface tensions. We propose a compact model that captures the essential features of the system to describe how a pure vertical vibration results in horizontal drop motion. This model provides an intuitive understanding of the underlying physics and explains how the surface asymmetry is the key for lateral drop motion.