Cloaking Dynamics on Lubricant-Infused Surfaces

Lubricant-infused surfaces (SLIPSs/LISs) enable omniphobicity by reducing droplet pinning through creation of an atomically smooth liquid-liquid interface. Although SLIPSs/LISs provide efficient omniphobicity, the need for lubricant adds additional barriers to heat and mass transport and affects three-phase contact line dynamics. Here, evaporation dynamics of microscale water droplets on SLIPSs/LISs are investigated using steady and transient methods. Although steady results demonstrate that evaporation on SLIPSs/LISs is identical to solid functional surfaces having equivalent apparent contact angle, transient measurements show significant increases in evaporation timescale. To understand the inconsistency, high-speed optical imaging is used to study the evaporating droplet free interface. Focal plane shift imaging enables the study of cloaking dynamics by tracking satellite microdroplet motion on the cloaked oil layer to characterize critical timescales. By decoupling the effect of substrate material and working fluid via experiments on both microstructured copper oxide and nanostructured boehmite with water and ethanol, it is demonstrated that lubricant cloaking cannot be predicted purely by thermodynamic considerations. Rather, coalescence dynamics, droplet formation, and surface interactions play important roles on establishing cloaking. The outcomes of this work shed light onto the physics of lubricant cloaking, and provide a powerful experimental platform to characterize droplet interfacial phenomena