Evaporation of squeezed water droplets between two parallel hydrophobic/superhydrophobic surfaces

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Abstract

Hypothesis: A liquid droplet is apt to be deformed within a compact space in various applications. The morphological change of a droplet and vapor accumulation in the confined space between two parallel surfaces with different gaps and surface wettability are expected to significantly affect the evaporation dynamics of the squeezed droplet therein. Experiments: Here the evaporation dynamics of a squeezed droplet between two parallel hydrophobic/superhydrophobic surfaces are experimentally explored. By reducing the surface gap from 1000 μm to 400 μm, the evolution of contact angle, contact radius and volume of the evaporating droplet are measured. A diffusion-driven model based on a two-parameter ellipsoidal segment geometry is developed to predict the morphology and volume evolution of a squeezed droplet during evaporation. Findings: Evaporation dynamics of a squeezed water droplet via the constant contact radius (CCR) mode, the constant contact angle (CCA) mode, or the mixed mode are experimentally observed. Confirmed by our ellipsoidal segment model, the evaporation of the squeezed droplet is significantly depressed with the decreasing surface gap, which is primarily attributed to vapor enrichment in a more confined geometry. A linear scaling law between droplet volume and evaporation time is unveiled, which is verified by a simplified cylindrical model.

Original languageEnglish
Pages (from-to)127-138
Number of pages12
JournalJournal of Colloid and Interface Science
Volume576
DOIs
StatePublished - Sep 15 2020

Funding

This work is financially supported by NSF CBET under grant number 1550299 and NSF ECCS under grant number 1808931 . The fabrication of the black silicon nanofibers was conducted at the Center for Nanophase Materials Sciences of Oak Ridge National Laboratory , which is a DOE Office of Science User Facility. This work is financially supported by NSF CBET under grant number 1550299 and NSF ECCS under grant number 1808931. The fabrication of the black silicon nanofibers was conducted at the Center for Nanophase Materials Sciences of Oak Ridge National Laboratory, which is a DOE Office of Science User Facility. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC0500OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes.

Keywords

  • Confined space
  • Diffusion-driven model
  • Squeezed droplet evaporation
  • Superhydrophobic

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