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Evaporation and condensation occur simultaneously at interfaces. Even when a sessile water droplet on a substrate evaporates to disappear eventually, the droplet absorbs water vapor from the surrounding air of a finite humidity. Exploiting a significant contrast in neutron scattering cross section between hydrogen and its isotope, deuterium, neutron radiography can quantify how much water vapor is absorbed into a sessile D \(_2\) O droplet. Although water vapor enters the droplet only via the air-droplet interface, absorbed water exists almost uniformly over the droplet, regardless of various sizes and contact angles we investigate. This spatial homogeneity also exists in the pendant droplet; absorbed H \(_2\) O is lighter than D \(_2\) O. To minimize flow-induced mixing, e.g., by capillary or Marangoni flow, we observe water vapor absorption into an open-ended capillary filled with D \(_2\) O. With no sample-wide mixing, the distribution of absorbed water indeed exhibits non-uniform distribution. These experiments demonstrate the usefulness of neutron radiography in studying mass transport processes.

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Condensation of the Vapor in Sessile Water Droplets and Open-Ended Water-Filled Capillaries Revealed by Neutron Radiography

  • 会议论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年

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  • Hyeonjun An,
  • Youngtak Koo,
  • Jiyong Cheon,
  • Pavel Trtik,
  • Joonwoo Jeong

摘要

Evaporation and condensation occur simultaneously at interfaces. Even when a sessile water droplet on a substrate evaporates to disappear eventually, the droplet absorbs water vapor from the surrounding air of a finite humidity. Exploiting a significant contrast in neutron scattering cross section between hydrogen and its isotope, deuterium, neutron radiography can quantify how much water vapor is absorbed into a sessile D \(_2\) O droplet. Although water vapor enters the droplet only via the air-droplet interface, absorbed water exists almost uniformly over the droplet, regardless of various sizes and contact angles we investigate. This spatial homogeneity also exists in the pendant droplet; absorbed H \(_2\) O is lighter than D \(_2\) O. To minimize flow-induced mixing, e.g., by capillary or Marangoni flow, we observe water vapor absorption into an open-ended capillary filled with D \(_2\) O. With no sample-wide mixing, the distribution of absorbed water indeed exhibits non-uniform distribution. These experiments demonstrate the usefulness of neutron radiography in studying mass transport processes.