Abstract:
Over the past decade, lubricant-infused surfaces (LIS) and slippery liquid-infused porous surfaces (SLIPS) have received significant attention in condensation applications owing to their low droplet-surface adhesion, enhanced droplet mobility and rapid condensate removal when compared to state-of-the-art (super)hydrophobic surfaces. In general, the infusing lubricants such as fluorinated Krytox and Silicone oils are phase invariant and exist in liquid phase during heat transfer applications. However, the use of phase invariant lubricants makes the LIS and SLIPS rigid and monotonous, having identical surface wettability, droplet adhesion and condensation droplet dynamics across all temperatures and conditions. Moreover, the liquid-liquid interaction induces additional challenges such as miscibility of the infused lubricant with the working fluid, encapsulation of the condensate droplet by the infused lubricant, termed as cloaking, and during prolonged condensation experiments, evaporation of the liquid lubricant. In the present study, we utilize bio-friendly, food-grade, coconut oil as a phase variant (PV) infusing lubricant to develop rationally designed nanostructured CuO based PV-SLIPS. The phase transition temperature of 25 degree C makes coconut oil infused PV-SLIPS the ideal candidate for condensation applications relevant in ambient conditions. The developed PV-SLIPS exhibit unique wettability and wetting mode, and imposes high or low condensatesurface adhesion states when subjected to temperatures below or higher than its phase transition temperature, respectively. Rigorous water vapor condensation experiments on PV-SLIPS in both solid (high droplet adhesion) and liquid (low droplet adhesion) states of the infused coconut oil reveal dropwise condensation, though the condensation rate and correspondingly the heat transfer coefficient differ due to the largely different droplet dynamics and droplet adhesion. This work not only shows the possibility of utilizing phase change materials as infusing lubricants, but also provides additional design considerations for developing durable and robust phase variant LIS and SLIPS.