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

We studied the short-time contact-linedynamics of a self-rewetting sessiledroplet 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 ofsurface tension gradients(Marangoni effect) to thedroplet motion was investigated. The temperature of the substrate in conjunction with the non-monotonicsurface tension/temperature dependence of the deformed self-rewettingdroplet 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 theliquid surface due to the strong surface-tension gradients. Our results demonstrate that the presence of strongsurface tension drivenflows at theliquid interface combined withdroplet deformation (contact-angle hysteresis) gives rise to complexdropletdynamics. 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 thedroplet motion overcoming gravity in some instances.

Source: Applied Physics Letters - December 5, 2016 Category: Physics Authors: Dimitrios Mamalis, Vasileios Koutsos and Khellil Sefiane Source Type: research