Shape of Water–Air Interface beneath a Drop on a Superhydrophobic Surface Revealed: Constant Curvature That Approaches Zero

Haimov, Boris; Pechook, Sasha; Ternyak, O.; Pokroy, Boaz

doi:10.1021/jp312650f

Cited by 20 publications

(26 citation statements)

References 37 publications

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“…Several studies have reported the use of laser scanning confocal microscopy (LSCM) technique to evaluate the wetting properties . Chesna et al exploited the confocal microscopy to determine the radius and height of small droplets (<1 mm), based on which the CA is computed using a spherical approximation of the droplet shape

θ = \cos^{- 1} (1 - \frac{h_{d}}{r_{d}})

…”

Section: Definition Of Surface Wettability: Beyond General Classificamentioning

confidence: 99%

Assessment and Interpretation of Surface Wettability Based on Sessile Droplet Contact Angle Measurement: Challenges and Opportunities

Kung

Sow

Zahiri

et al. 2019

Adv Materials Inter

130

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www.advmatinterfaces.de the sessile CA remains the favored method for quantifying wettability, mostly due to its conceptual and measurement simplicity. [9,31] However, the classification on the basis of the cut-off CA of 90° has attracted criticism. [32,33] The simplistic evaluation criteria of relative wettability are becoming inadequate in satisfying the needs of superwettability studies to classify different wetting phenomena. [34] Several works have questioned the accuracy of the sessile-droplet measurement as the CA value approaches the limits of 0° or 180°. [35,36] Yet, evaluation of surfaces in the superhydrophobic (CA > 150°) and superhydrophilic (CA < 10°) regimes is central in the development of enhanced wettabilities. Moreover, the interpretation of the CA results is often complicated by several factors, including surface smoothness, heterogeneity and cleanliness. [37] The Chun Haow Kung obtained his B.A.Sc. and M.A.Sc. in Chemical Engineering at the University of British Columbia (UBC). His graduate work with Prof. Mérida's group at UBC focused on the development and application of novel wetting characterization techniques, smart stimuli-responsive materials as well as electrochemical and hydrogen energy systems. He is currently a Research Scientist at Ballard Power Systems Inc. where he continues to pursue his interest in the polymer electrolyte membrane (PEM) fuel cell technology. Beniamin Zahiri is currently a researcher in the University of Illinois at Urbana-Champaign

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θ = \cos^{- 1} (1 - \frac{h_{d}}{r_{d}})

…”

Section: Definition Of Surface Wettability: Beyond General Classificamentioning

confidence: 99%

Assessment and Interpretation of Surface Wettability Based on Sessile Droplet Contact Angle Measurement: Challenges and Opportunities

Kung

Sow

Zahiri

et al. 2019

Adv Materials Inter

130

View full text Add to dashboard Cite

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“…the degree of liquid penetration inside the roughness valleys and the geometric configuration of LA interface. Distinct metastable Cassie states, corresponding to unique values of penetration depth and/or interfacial orientation have been experimentally confirmed using various imaging and acoustic techniques 7,8,10 . Recently, we have deduced a characteristic set of equations which provides an implicit correlation of penetration depth of a liquid with the apparent contact angle 11 .…”

Section: Introduction: Origin Of Penetration Depthmentioning

confidence: 89%

“…A homogeneous regime and a heterogeneous regime with no penetration are also termed as Wenzel wetting state and Cassie wetting state, respectively. Current literature suggests the existence of a heterogeneous wetting regime with partial liquid penetration, also termed as metastable Cassie states [3][4][5][6][7][8][9][10] .A metastable Cassie state is characterized by its penetration depth, i.e. the degree of liquid penetration inside the roughness valleys and the geometric configuration of LA interface.…”

Section: Introduction: Origin Of Penetration Depthmentioning

confidence: 99%

Design of a robust superhydrophobic surface: thermodynamic and kinetic analysis

Sarkar

Kietzig

2015

Soft Matter

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The design of a robust superhydrophobic surface is a widely pursued topic. While many investigations are limited to applications with high impact velocities (for raindrops of the order of a few m/s), the essence of robustness is yet to be analyzed for applications involving quasi-static liquid transfer. To achieve robustness with high impact velocities, the surface parameters (geometrical details, chemistry) have to be selected from a narrow range of permissible values, which often entail additional manufacturing costs. From the dual perspectives of thermodynamics and mechanics, we analyze the significance of robustness for quasi-static drop impact, and present the range of permissible surface characteristics. For surfaces with a Young's contact angle greater than 90° and square micropillar geometry, we show that robustness can be enforced when an intermediate wetting state (sagged state) impedes transition to a wetted state (Wenzel state). From the standpoint of mechanics, we use available scientific data to prove that a surface with any topology must withstand a pressure of 117 Pa to be robust. Finally, permissible values of surface characteristics are determined, which ensure robustness with thermodynamics (formation of sagged state) and mechanics (withstanding 117 Pa).

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“…This result is consistent with the findings of Pokroy and co-workers,w hich showed small curvature of the liquid interface in the whole droplet. [36] Thev isualized observation of the inside morphology can also be used to clarify some wetting phenomena, including calculations of the contact angle, [37] intrinsic mechanism for the low adhesion, and the small sliding angle of the liquid on superhydrophobic Cassie surfaces (see note S5).…”

Section: Methodsmentioning

confidence: 99%

Direct Insight into the Three‐Dimensional Internal Morphology of Solid–Liquid–Vapor Interfaces at Microscale

Yang

Cao

et al. 2015

Angew Chem Int Ed

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Solid-liquid-vapor interfaces dominated by the three-phase contact line, usually performing as the active center in reactions, are important in biological and industrial processes. In this contribution, we provide direct three-dimensional (3D) experimental evidence for the inside morphology of interfaces with either Cassie or Wenzel states at micron level using X-ray micro-computed tomography, which allows us to accurately "see inside" the morphological structures and quantitatively visualize their internal 3D fine structures and phases in intact samples. Furthermore, the in-depth measurements revealed that the liquid randomly and partly located on the top of protrusions on the natural and artificial superhydrophobic surfaces in Cassie regime, resulting from thermodynamically optimal minimization of the surface energy. These new findings are useful for the optimization of classical wetting theories and models, which should promote the surface scientific and technological developments.

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Shape of Water–Air Interface beneath a Drop on a Superhydrophobic Surface Revealed: Constant Curvature That Approaches Zero

Cited by 20 publications

References 37 publications

Assessment and Interpretation of Surface Wettability Based on Sessile Droplet Contact Angle Measurement: Challenges and Opportunities

Assessment and Interpretation of Surface Wettability Based on Sessile Droplet Contact Angle Measurement: Challenges and Opportunities

Design of a robust superhydrophobic surface: thermodynamic and kinetic analysis

Direct Insight into the Three‐Dimensional Internal Morphology of Solid–Liquid–Vapor Interfaces at Microscale

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