Quantum Mechanical Simulation and Experimental Characterization of Dropwise Condensation on Nanotextured Surfaces with Oil Infusion

Abstract

Dropwise condensation has been well-known and extensively studied for its outstanding heat transfer performance. Lubricant-infused surfaces (LISs) enhance dropwise condensation for liquids with high surface tension by minimizing the pinning force and accelerating droplet removal. Moreover, LISs are effective for enabling dropwise condensation of low-surface-tension liquids. In this work, a new phenomenon of satellite droplet condensation on LISs is reported and characterized with environmental scanning electron microscopy (ESEM) for different lubricants. The presence of satellite droplets provides direct evidence for the existence of the ultrathin lubricant cloaking film, which is also confirmed with Raman spectra. Especially, we show the 'non-spreading' BMIm ionic liquid is in fact cloaking during the transient condensation process. In addition to the lubricant, the surface coating also plays an important role in promoting dropwise condensation. As a robust alternative to the conventional silane coatings, the intrinsic wettability of ceria is interesting for researchers in different areas. Using a novel quantum simulation method based on density functional theory (DFT), we study the wettability of stoichiometric and reduced CeO2(111) surfaces to clarify the existing discrepancy between simulation and experimental studies. Our findings show that the main reason for the discrepancy is the simulated surface is stoichiometric, while fabricated samples are reduced with surface oxygen vacancy. Water condensation experiments in ESEM show the sputter-coated surfaces promote dropwise condensation after aging. Further, we extend the DFT method to study the effects of polar interaction and temperature on the wettability in a system involving solid, water, and oil, simultaneously. The counter-intuition trend in contact angles of the polar liquids (i.e. water, ethylene glycol, glycerol) is quantitatively analyzed, which shows a linear relationship between the adhesion energy and electrostatic potential at solid-liquid interface. The DFT prediction for thermal effect on wettability of crystal surface agrees well with our experimental measurements. By integrating ESEM, confocal Raman spectroscopy, and quantum simulation, this thesis provides physical insights into cloaking phenomenon in condensation on LISs and hydrophobic rare-earth oxide coating for stable dropwise condensation.

Date of Award	Dec 2020
Original language	American English
Supervisor	TJ Zhang (Supervisor)