Thermocapillary lubricant migration on textured surfaces-a review of theoretical and experimental insights

Thermocapillary migration in tribological systems such as gearboxes, piston ring-liner assemblies, or bearings can lead to lubricant starvation and, consequently, to severe damages. Due to surface tension gradients induced by local temperature gradients on the frictionally heated surface, lubricant may flow out of the hotter contact zone to colder adjacent regions. In order to manipulate lubricant migration, several approaches exist to create migration barriers or to guide lubricant in a well-defined way back into the contact. These approaches are either based upon surface topography (designed surface textures) and/or surface chemistry (designed chemical patterns). In this review article, the state-of-the-art regarding thermocapillary migration is summarized from a theoretical and experimental point of view. After a brief introduction, theoretical models are presented to introduce the underlying theory of droplet spreading and thermocapillary migration. Subsequently, the influence of surface textures and chemical patterns on thermocapillary migration and the possibilities to use these approaches to manipulate lubricant migration are discussed. After addressing applied research in this field and potential applications, current challenges and future research directions are presented before closing with general conclusions.