TY - JOUR
T1 - The most stable state of a droplet on anisotropic patterns
T2 - Support for a missing link
AU - Sun, Yujin
AU - Jiang, Youhua
AU - Choi, Chang Hwan
AU - Xie, Guangyuan
AU - Liu, Qingxia
AU - Drelich, Jaroslaw W.
N1 - Publisher Copyright:
© 2018 ICE Publishing. All Rights Reserved.
PY - 2018/1/3
Y1 - 2018/1/3
N2 - Surface tension and capillary forces were measured for water droplets in contact with anisotropic hydrophobic patterns made of microscopic ridges and grooves using a microbalance. Integrated with a charge-coupled device camera, the instrument allowed capturing of the synchronous images of a droplet during its spreading, compression, stretching and detachment. These images were used to analyze the evolution of the droplet shape and quantify its base diameter and contact angle in both the longitudinal and traverse directions. The experiments confirmed that a water droplet spreads preferentially along the longitudinal direction, on top of the ridges, following the continuity of the solid and producing asymmetry in the drop shape. Switching the droplet wetting mode from advancing to receding causes the droplet to symmetrize its shape. It was found that the maximum adhesion between the droplet and hydrophobic pattern coincides with droplet base circularity and apparent contact angles of nearly identical values measured in the longitudinal and traverse directions. These findings confirm that the most stable configuration for a liquid droplet on a rough solid surface appears only when the droplet base is axisymmetric. It is also demonstrated that the Cassie-Baxter equation pertains only to the droplet in the most stable state, where the excess free energy is minimized.
AB - Surface tension and capillary forces were measured for water droplets in contact with anisotropic hydrophobic patterns made of microscopic ridges and grooves using a microbalance. Integrated with a charge-coupled device camera, the instrument allowed capturing of the synchronous images of a droplet during its spreading, compression, stretching and detachment. These images were used to analyze the evolution of the droplet shape and quantify its base diameter and contact angle in both the longitudinal and traverse directions. The experiments confirmed that a water droplet spreads preferentially along the longitudinal direction, on top of the ridges, following the continuity of the solid and producing asymmetry in the drop shape. Switching the droplet wetting mode from advancing to receding causes the droplet to symmetrize its shape. It was found that the maximum adhesion between the droplet and hydrophobic pattern coincides with droplet base circularity and apparent contact angles of nearly identical values measured in the longitudinal and traverse directions. These findings confirm that the most stable configuration for a liquid droplet on a rough solid surface appears only when the droplet base is axisymmetric. It is also demonstrated that the Cassie-Baxter equation pertains only to the droplet in the most stable state, where the excess free energy is minimized.
KW - Adhesion
KW - Contact angle
KW - Roughness
UR - http://www.scopus.com/inward/record.url?scp=85044409342&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85044409342&partnerID=8YFLogxK
U2 - 10.1680/jsuin.17.00064
DO - 10.1680/jsuin.17.00064
M3 - Article
AN - SCOPUS:85044409342
SN - 2050-6252
VL - 6
SP - 133
EP - 140
JO - Surface Innovations
JF - Surface Innovations
IS - 3
ER -