On the motion of a sessile drop on an incline: Effect of non-monotonic thermocapillary stresses

Abstract

We studied the short-time contact-line dynamics of a self-rewetting sessile droplet sliding “freely” on a silicone oil layer, on an inclined, uniformly heated substrate under non-isothermal conditions (liquid–solid). The effect of thermocapillarity and the contribution of surface tension gradients (Marangoni effect) to the droplet motion was investigated. The temperature of the substrate in conjunction with the non-monotonic surface tension/temperature dependence of the deformed self-rewetting droplet was found to significantly affect the early-stage inertial-capillary spreading regime. Infrared (IR) thermography images were also acquired to investigate the generation of thermal patterns at the liquid surface due to the strong surface-tension gradients. Our results demonstrate that the presence of strong surface tension driven flows at the liquid interface combined with droplet deformation (contact-angle hysteresis) gives rise to complex droplet dynamics. The interplay between thermocapillary stresses and body forces results in enhanced spreading rates, temporal non-monotonic dependence of the contact-line speed, as well as the droplet motion overcoming gravity in some instances.