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.
Spreading of a thin droplet on a soft substrate
A thin liquid droplet spreads on a soft viscoelastic substrate with arbitrary rheology. Lubrication theory is applied to the governing field equations in the liquid and solid domains, which are coupled through the free boundary at the solid–liquid interface, to derive a set of reduced equations that describe the spreading dynamics. Fourier transform techniques and the finite difference method are used to construct a solution for the dynamic liquid–gas and solid–liquid interface shapes, as well as the macroscopic contact angle. Substrate properties affect the spreading dynamics through the contact angle and internal droplet flow fields, and these mechanisms are revealed. Increased substrate softness increases the spreading rate, whereas increased viscoelasticity decreases the spreading rate. For the case of a purely elastic substrate, the spreading power-law exponent recovers Tanner's law in the rigid limit and increases with substrate softness.
more » « less- Award ID(s):
- 1750208
- PAR ID:
- 10484225
- Publisher / Repository:
- Cambridge Press
- Date Published:
- Journal Name:
- Journal of Fluid Mechanics
- Volume:
- 971
- ISSN:
- 0022-1120
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/jfm.2023.673
