title: Direct and accurate measurement of size dependent wetting behaviors for sessile water droplets.
abstract: The size-dependent wettability of sessile water droplets is an important matter in wetting science. Although extensive studies have explored this problem, it has been difficult to obtain empirical data for microscale sessile droplets at a wide range of diameters because of the flaws resulting from evaporation and insufficient imaging resolution. Herein, we present the size-dependent quantitative change of wettability by directly visualizing the three phase interfaces of droplets using a cryogenic-focused ion beam milling and SEM-imaging technique. With the fundamental understanding of the formation pathway, evaporation, freezing, and contact angle hysteresis for sessile droplets, microdroplets with diameters spanning more than three orders of magnitude on various metal substrates were examined. Wetting nature can gradually change from hydrophobic at the hundreds-of-microns scale to super-hydrophobic at the sub-μm scale, and a nonlinear relationship between the cosine of the contact angle and contact line curvature in microscale water droplets was demonstrated. We also showed that the wettability could be further tuned in a size-dependent manner by introducing regular heterogeneities to the substrate.
authors.affiliation: Center for Biomaterials, Korea Institute of Science &Technology, Seoul, 02792, South Korea.
authors.forename: Jimin
authors.initials: J
authors.lastname: Park
authors.affiliation: Center for Biomaterials, Korea Institute of Science &Technology, Seoul, 02792, South Korea.
authors.forename: Hyung-Seop
authors.initials: HS
authors.lastname: Han
authors.affiliation: Center for Biomaterials, Korea Institute of Science &Technology, Seoul, 02792, South Korea.|Korea University of Science and Technology, Daejeon, 34113, South Korea.
authors.forename: Yu-Chan
authors.initials: YC
authors.lastname: Kim
authors.affiliation: Korea University of Science and Technology, Daejeon, 34113, South Korea.|Advanced Analysis Center, Korea Institute of Science &Technology, Seoul, 02792, South Korea.
authors.forename: Jae-Pyeong
authors.initials: JP
authors.lastname: Ahn
authors.affiliation: Center for Biomaterials, Korea Institute of Science &Technology, Seoul, 02792, South Korea.
authors.forename: Myoung-Ryul
authors.initials: MR
authors.lastname: Ok
authors.affiliation: Advanced Analysis Center, Korea Institute of Science &Technology, Seoul, 02792, South Korea.
authors.forename: Kyung Eun
authors.initials: KE
authors.lastname: Lee
authors.affiliation: School of Advanced Materials Engineering, Kookmin University, Seoul, 02707, South Korea.
authors.forename: Jee-Wook
authors.initials: JW
authors.lastname: Lee
authors.affiliation: School of Advanced Materials Engineering, Kookmin University, Seoul, 02707, South Korea.
authors.forename: Pil-Ryung
authors.initials: PR
authors.lastname: Cha
authors.affiliation: Center for Biomaterials, Korea Institute of Science &Technology, Seoul, 02792, South Korea.|Korea University of Science and Technology, Daejeon, 34113, South Korea.
authors.forename: Hyun-Kwang
authors.initials: HK
authors.lastname: Seok
authors.affiliation: Center for Biomaterials, Korea Institute of Science &Technology, Seoul, 02792, South Korea.|Korea University of Science and Technology, Daejeon, 34113, South Korea.
authors.forename: Hojeong
authors.initials: H
authors.lastname: Jeon