Thermocapillary motion of a solid cylinder near a liquid–gas interface: Janus geometry

Abstract

In this work, an analytical model is developed for the thermocapillary propulsion of a solid cylinder near a convective liquid–gas interface. Thermocapillarity originates from the temperature-induced surface tension gradients at the liquid–gas interface when the surface temperature of a cylinder residing near the interface differs from the liquid phase. In this work, we consider Janus cylinders with piece-wise constant surface temperatures or heat fluxes. In the former case, we addressed the Gibbs' phenomenon induced by the points of discontinuity. The developed procedure allowed us to study the dynamics of the general case of cylinders with different surface ratios of piece-wise constant temperatures and find the configurations inducing the largest velocities. Most Janus configurations result in motion of the cylinder parallel to the liquid–gas interface. The efficiency of the propulsion parallel to the liquid–gas interface is of the same order of magnitude as the propulsion efficiency of an isotropic cylinder normal to the interface. Considering the emerging interest of scientific community in mechanisms beyond the catalytically induced propulsion, this study may help to shed light on new ways to modulate the propulsion.