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  • Letter
  • Open Access

Contact line length dominance in evaporation of confined nonspherical droplets

Gun Oh1,2, Jae-Hong Lim3, Sung Hoon Kang2,*, and Byung Mook Weon1,4,†

  • 1Soft Matter Physics Laboratory, School of Advanced Materials Science and Engineering, SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 16419, Republic of Korea
  • 2Department of Mechanical Engineering and Hopkins Extreme Materials Institute, Johns Hopkins University, Baltimore, Maryland 21218, USA
  • 3Pohang Accelerator Laboratory, POSTECH, 80 Jigokro-127-beongil, Nam-gu, Pohang, Gyeongbuk 37673, Republic of Korea
  • 4Research Center for Advanced Materials Technology, Sungkyunkwan University, Suwon 16419, Republic of Korea

  • *shkang@jhu.edu
  • †bmweon@skku.edu
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Phys. Rev. Research 6, L012026 – Published 8 February, 2024

DOI: https://doi.org/10.1103/PhysRevResearch.6.L012026

Abstract

Free droplets are spherical within capillary lengths and become nonspherical when trapped in a confined space. Confined nonspherical droplets are as common as spherical droplets. Yet, their evaporation dynamics are not fully understood because of their geometrical complexity. We use monochromatic synchrotron x-ray microtomography to investigate the evaporation dynamics of confined nonspherical water droplets trapped by micropillars based on three-dimensional geometrical information with time. We find two types of confined nonspherical droplets: Wenzel droplets with single-sided air-water interfaces, and Cassie-Baxter droplets with double-sided interfaces. Both droplets show similar sphericity at large volumes but approach different ones at small volumes: Wenzel droplets follow a thin film limit, whereas Cassie-Baxter droplets follow a spherical sessile limit. Despite the geometrical complexity of confined nonspherical droplets, the vapor diffusion mechanism suggests that the evaporative flux is maximal at the contact line, which governs the evaporation dynamics, as proven by observations. The proportionality of the evaporation rate to the contact line length demonstrates the contact-line-length-dominant evaporation dynamics of confined nonspherical droplets. The findings of this study can unify the evaporation mechanism for spherical sessile and confined nonspherical droplets, even with geometric complexity.

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Phys. Rev. Research 6, L012026– Published 8 February, 2024
  • Received 18 September 2023
  • Accepted 10 January 2024
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