Surface roughness and orientation effects on the thermo-capillary migration of a droplet of paraffin oil

Abstract

The Marangoni effect is an important phenomenon in which a surface tension gradient drives liquid flow to regions of high surface tension to form thin liquid films. Temperature gradient, evaporation, disparity of viscosity and surface roughness are all significant factors that can affect the oil migration behaviour. The purpose of this study was to determine the influence of surface roughness and surface topography orientation on migration behaviour under various temperature gradients. Specimens with different surface roughness were fabricated, and the migration behaviour of paraffin oil on each specimen was investigated using home-built testing equipment. The results show that the roughest surface with the grinding scars parallel to the temperature gradient exhibited the fastest migration velocity. Increasing the viscosity of paraffin oil decreased the influence of roughness on migration behaviour. Our results also indicate that the orientation of grinding scars determines the behaviour of temperature-driven migration, which guides the moving direction of drops and may act as a barrier impeding drop movement along the temperature gradient. When the temperature gradient was increased to a certain value, the barrier was broken through and the temperature gradient became the dominant factor affecting oil migration direction.