Finite retention in non-wetting lubricant-infused surfaces*

Surfaces patterned with long parallel grooves infused with a lubricating fluid (LIS) can be used for drag reduction, anti-fouling, and heat transfer enhancement in marine applications. Design criteria have been established to mitigate failure modes mainly related to lubricant drainage when the surfaces are exposed to shear flows. A critical requirement to assure their robustness is that the lubricant has to wet the surface when surrounded by the working liquid. Technical constraints related to the experimental apparatus or to the choice of materials can be an obstacle to meet such condition. In this study a non-wetting LIS, where the canonical condition is violated, is manufactured and tested in a new turbulent water channel facility. We demonstrate that, despite the energetic unfavourable condition, a finite length of lubricant is retained in a stable manner even when subjected to a turbulent flow. In comparison, when the configuration of a wetting lubricant is applied on the same LIS geometry and fluids, the lubricant drainage happens much earlier if retention barriers are not used. We formulate an analytical model which shows, in agreement with the experimental results, that the contact line hysteresis has a critical role in the lubricant retention mechanism.