Lubricant infused surfaces (LIS or SLIPS) have potential to enhance a variety of applications due to their non-wetting characteristics. Recently, LIS and SLIPS have been shown to greatly improve dropwise condensation heat transfer performance by enabling ultra-low contact angle hysteresis (< 5°) and droplet-surface adhesion. The low adhesion characteristics arise from the ultra-smooth liquid-liquid interface that depends on the lubricating fluid remaining infused into the surface by capillary forces. A key limiting phenomenon of LIS and SLIPS is cloaking, whereby the infused lubricant spreads and forms a very thin layer (∼100 nm) over liquid droplet residing on the substrate. This can lead to degradation due to drainage of the lubricant layer. Cloaking involves several fluid interfaces between the lubricant, droplet and air, and the resolution of the lubricant-droplet interface is essential to cloaking imaging and characterization. Our work involves goniometric measurements of advancing and receding contact angles, imaging of cloaked water droplets on LIS and SLIPS, and the characterization of cloaking during shear induced flow. The LIS and SLIPS substrates were created by spin coating lubricants of various viscosities (5 – 2712 cSt) onto superhydrophobic nanostructured boehmite (AlO(OH)). Cloaking effects were observed by inhibition of water droplet evaporation (Fig. a). Furthermore, the lubricantdroplet interface for non-cloaking droplets was resolved using lubricant-miscible dyes (Fig. a). Cloaking was also characterized by studying shear induced flow of both condensate and artificially injected droplets, resulting in lubricant drainage as shown in Figures (b) and (c). The results of this work not only provide a basis for understanding the lubricant-droplet interactions on LIS and SLIPS, but also material design guidelines for future LIS and SLIPS coatings.
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Droplet Cloaking Imaging and Characterization
Alex Wu,
Alex Wu
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign
alexwu2@illinois.edu
alexwu2@illinois.edu
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Nenad Miljkovic
Nenad Miljkovic
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign
nmiljkov@illinois.edu
nmiljkov@illinois.edu
Search for other works by this author on:
Alex Wu
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign
alexwu2@illinois.edu
alexwu2@illinois.edu
Nenad Miljkovic
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign
nmiljkov@illinois.edu
nmiljkov@illinois.edu
1Corresponding author.
J. Heat Transfer. Mar 2018, 140(3): 030902
Published Online: February 16, 2018
Article history
Received:
November 1, 2017
Revised:
December 27, 2017
Citation
Wu, A., and Miljkovic, N. (February 16, 2018). "Droplet Cloaking Imaging and Characterization." ASME. J. Heat Transfer. March 2018; 140(3): 030902. https://doi.org/10.1115/1.4039167
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