Srinivas Bengaluru Subramanyam

Mechanism of frost formation on lubricant-impregnated surfaces.

Frost formation is a major problem affecting a variety of industries including transportation, power generation, construction, and agriculture. Currently used active chemical, thermal, and mechanical techniques of ice removal are time-consuming and costly. The use of nanotextured coatings infused with perfluorinated oil has recently been proposed as a simple passive antifrosting and anti-icing method. However, we demonstrate that the process of freezing subcooled condensate and frost formation on such lubricant-impregnated surfaces is accompanied by the migration of the lubricant from the wetting ridge and from within the textured substrate to the surface of frozen droplets. For practical applications, this mechanism can comprise the self-healing and frost-repelling characteristics of lubricant impregnated-surfaces, regardless of the underlying substrates topography. Thus, further research is necessary to develop liquid-texture pairs that will provide a sustainable frost suppression method.

Ice Adhesion on Lubricant-Impregnated Textured Surfaces

Ice accretion is an important problem and passive approaches for reducing ice-adhesion are of great interest in various systems such as aircrafts, power lines, wind turbines, and oil platforms. Here, we study the ice-adhesion properties of lubricant-impregnated textured surfaces. Force measurements show ice adhesion strength on textured surfaces impregnated with thermodynamically stable lubricant films to be higher than that on surfaces with excess lubricant. Systematic ice-adhesion measurements indicate that the ice-adhesion strength is dependent on texture and decreases with increasing texture density. Direct cryogenic SEM imaging of the fractured ice surface and the interface between ice and lubricant-impregnated textured surface reveal stress concentrators and crack initiation sites that can increase with texture density and result in lowering adhesion strength. Thus, lubricant-impregnated surfaces have to be optimized to outperform state-of-the-art icephobic treatments.

How droplets nucleate and grow on liquids and liquid impregnated surfaces

Condensation on liquids has been studied extensively in context of breath figure templating, materials synthesis and enhancing heat transfer using liquid impregnated surfaces. However, the mechanics of nucleation and growth on liquids remains unclear, especially on liquids that spread on the condensate. By examining the energy barriers of nucleation, we provide a framework to choose liquids that can lead to enhanced nucleation. We show that due to limits of vapor sorption within a liquid, nucleation is most favoured at the liquid-air interface and demonstrate that on spreading liquids, droplet submergence within the liquid occurs thereafter. We provide a direct visualization of the thin liquid profile that cloaks the condensed droplet on a liquid impregnated surface and elucidate the vapour transport mechanism in the liquid films. Finally, we show that although the viscosity of the liquid does not affect droplet nucleation, it plays a crucial role in droplet growth.

Designing Ultra-Low Hydrate Adhesion Surfaces by Interfacial Spreading of Water-Immiscible Barrier Films

Clathrate hydrates are icelike solid substances that can form inside oil and gas pipelines and are responsible for flow blockages, sometimes leading to catastrophic failures. Minimizing hydrate formation and adhesion on pipeline surfaces can effectively address this problem. In this paper, we achieve the lowering of the adhesion of cyclopentane hydrates by promoting a cyclopentane barrier film between the hydrate and solid surface. The presence of this interfacial liquid film depends on the relative spreading of cyclopentane on the solid surface in the presence of water. We study the role of surface chemistry and surface texture on the spreading characteristics of such interfacial films and their impact on hydrate adhesion. The use of the spreading coefficients as design parameters could take us a step closer to the development of effective passive antihydrate surfaces.

CHAPTER 10: Lubricant-Impregnated Surfaces

Lubricant-impregnated surfaces comprising a porous or textured solid and a liquid lubricant give rise to many novel properties. In this chapter, we review how to achieve a stable lubricant-impregnated surface and discuss its basic features including the wetting ridge and lubricant cloak that are relevant to most implementations. Next, applications of lubricant-impregnated surfaces are detailed including condensation, anti-icing, anti-fouling, fluid mobility, optics, and active surfaces. In each application, the design of a lubricant-impregnated surface has particularly relevant criteria, and both the achievements and current shortcomings of this technology are discussed.