On the Motion of a Sessile Drop on an Incline: Effect of Non-Monotonic Thermocapillary Stresses

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 nonisothermal 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 were 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) give rise to complex droplet dynamics. The interplay between thermocapillary stresses and body forces result in enhanced spreading rates, temporal non-monotonic dependence of the contact-line speed as well as the droplet motion overcoming gravity in some instances.