Drop dynamics on slippery liquid infused porous surfaces

Abstract

Slippery liquid-infused porous surfaces (SLIPS) have been introduced to enhance the mobility of liquid drops by minimising interaction with solid surfaces. The growing importance of SLIPS has resulted in useful applications in a wide range of fields and industrial applications. Despite recent advances, a quantitative mechanistic explanation for the formation of the lubricant ridge and its impact on drop dynamics remains elusive. In this study, we investigated the interaction of drops with SLIPS in a systematic approach using experiments and numerical modelling to quantify both equilibrium and dynamic properties.

The first part of the results reveals that drops self-propel on the lubricant film immediately after deposition, and we speculate that this mechanism can be due to the presence of a dimple which breaks the symmetry and causing a pressure imbalance. As a result, the drop self-propels towards the region with thicker lubricants. In the second part of the results, a modified relation between the apparent contact angle and the lubricant ridge size is validated both experimentally and numerically. We highlighted the flaws in a previously proposed model and developed a modified numerical model that accounts for both gravity effects and small ridges. Also, we introduced a scaling relation for estimating the drop volume from the drop shape that does not require an absolute scale.

In the last part of the results, we developed a theoretical model using the Landau-Levich-Derjaguin mechanism of film formation to predict the relation between lubricant ridge height and drop velocity in a steady state which shows a promising agreement with our experimental results. This model also allows to compute the drop mobility which showed that the viscous dissipation of a moving drop indeed depends on the lubricant ridge size and that this can affect the power law relation between the Capillary number and the Bond number. However, the effect of the additional friction on drop mobility is almost exactly balanced by the extra mass in lubricant ridge. The power relation remains valid with the same exponent, but the drop mobility has to be replaced with an effective drop mobility taking both effects into account.

Date of Award	30 Jul 2024
Original language	English
Awarding Institution	Northumbria University
Supervisor	Ciro Semprebon (Supervisor), Hamdi Torun (Supervisor) & Prashant Agrawal (Supervisor)