Revisited Cassie's law to incorporate microstructural capillary effects

Dover, Coinneach Mackenzie; Sefiane, Khellil

doi:10.1103/physrevfluids.4.081601

Cited by 7 publications

(5 citation statements)

References 40 publications

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“…Mackenzie-Dover and Sefiane incorporated microstructural capillary effects to modify the Cassie's equation in an experimental study [83]. They fabricated hydrophobized surface patterns, having flat-topped square micropillars with distinct pillar size and spacing via photolithography and deep reactive-ion etching.…”

Section: Direct Testing Of Wenzel and Cassie Equationsmentioning

confidence: 99%

“…In addition, it was reported that the liquid-gas portion of the contact line was distorted at the pillar edges and, although the extent of the distortion could not be quantified, it was possible to predict the experimental contact angles by considering the effect of capillary bridging. The capillary region was assumed to be semicircular and half of the width of a pillar was extended into the liquid-gas region of the contact line in these studies [83].…”

Section: Direct Testing Of Wenzel and Cassie Equationsmentioning

confidence: 99%

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Dependency of Contact Angles on Three-Phase Contact Line: A Review

Erbil

2021

Colloids and Interfaces

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The wetted area of a sessile droplet on a practical substrate is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, contact angles of droplets have been studied for more than two hundred years, there are still some unanswered questions. In the last two decades, it was experimentally proven that the advancing and receding contact angles, and the contact angle hysteresis of rough and chemically heterogeneous surfaces, are determined by interactions of the liquid and the solid at the three-phase contact line alone, and the interfacial area within the contact perimeter is irrelevant. However, confusion and misunderstanding still exist in this field regarding the relationship between contact angle and surface roughness and chemical heterogeneity. An extensive review was published on the debate for the dependence of apparent contact angles on drop contact area or the three-phase contact line in 2014. Following this old review, several new articles were published on the same subject. This article presents a review of the novel articles (mostly published after 2014 to present) on the dependency of contact angles on the three-phase contact line, after a short summary is given for this long-lasting debate. Recently, some improvements have been made; for example, a relationship of the apparent contact angle with the properties of the three-phase line was obtained by replacing the solid–vapor interfacial tension term, γSV, with a string tension term containing the edge energy, γSLV, and curvature of the triple contact line, km, terms. In addition, a novel Gibbsian thermodynamics composite system was developed for a liquid drop resting on a heterogeneous multiphase and also on a homogeneous rough solid substrate at equilibrium conditions, and this approach led to the same conclusions given above. Moreover, some publications on the line energy concept along the three-phase contact line, and on the “modified” Cassie equations were also examined in this review.

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Section: Direct Testing Of Wenzel and Cassie Equationsmentioning

confidence: 99%

Section: Direct Testing Of Wenzel and Cassie Equationsmentioning

confidence: 99%

Dependency of Contact Angles on Three-Phase Contact Line: A Review

Erbil

2021

Colloids and Interfaces

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“…Here, the metaskin is made of self‐assembled silica nanoparticles, where different microsized air pockets are randomly anchored between the nanosurface and water, thus forming an effective stable water/air interface with extreme acoustic impedance mismatching. According to the Cassie's law, [ 46 ] a water droplet has a nearly spherical shape on the rough surface of metaskins to minimize the surface energy, whereas it is spread on the bare metal plate, as shown by the insets of Figure 1. Here, it needs to be pointed out that the extreme impedance mismatch on the metaskin surface holds for broadband, which enables a wide‐spectrum modulation for ultrasound transmission (e.g., 1–5 MHz).…”

Section: Resultsmentioning

confidence: 99%

Generating Multistructured Ultrasound via Bioinspired Metaskin Patterning for Low‐Threshold and Contactless Control of Living Organisms

Zhou

et al. 2022

Adv Funct Materials

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Metasurfaces of the subwavelength thicknesses provide a distinctive route for acoustic wave manipulation. Based on the advanced 3D printing, those judiciously designed 2D metamaterials enable intriguing effects such as abnormal reflection, transmission, and absorption. However, acoustic metasurfaces, with strong wave–structure interactions in subwavelength scales, have encountered a big challenge of being acoustically transparent due to the insufficient impedance mismatch underwater. Here, reconfigurable bioinspired metaskin patterning for generating multistructured waterborne ultrasound is proposed. The nanostructured metaskin exhibits the “lotus effect,” with the thickness of only 70 μm (≈1/20 wavelength at 1 MHz) and a tremendous impedance mismatch (≈0.0001 transmission) for ultrasound. By depositing the strippable metaskins via self‐assembly into different patterns, the focusing, the vortex, and the Talbot structured ultrasound beams are implemented, respectively. The multistructured ultrasound has the patterned intensity fields of energy redistribution, where even weak field enhancement at low frequencies can activate the living organisms directly without using microbubbles, which enables low‐threshold and contactless behavior control via the mechanical stimulus.

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“…Thus, it does not change the wetting dynamics to a large extent. Recently, Mackenzie Dover and Sefiane also found that after the critical spacing between the pillars, the hydrophobic nature of the surface and the contact angle of the droplet do not change much. A similar behavior can also be seen for pillar size S = 10 μm (see Figure b).…”

Section: Resultsmentioning

confidence: 99%

Wetting Dynamics of a Water Droplet on Micropillar Surfaces with Radially Varying Pitches

2020

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The wetting dynamics of a sessile droplet on square micropillar substrates with radially varying pitches, prepared on silicon wafers using a photolithography technique, is investigated experimentally. Two configurations are considered, namely, substrates with radially increasing pitch and radially decreasing pitch. The droplet initially placed at the center experiences a wettability gradient because of the variation in pitch of the micropillar substrate leading to complex wetting dynamics. We observed that the droplet remains in the Cassie–Baxter state in the case of a radially increasing pitch and exhibits a higher contact angle than that on a smooth surface during its spreading stage. In contrast, the droplet experiences the Wenzel condition in the case of a radially decreasing pitch and assumes a lower contact angle relative to that observed on a smooth surface. The wetted diameter of the droplet in the radially decreasing pitch configuration is found to be smaller than that observed in the radially increasing pitch configuration. Our study also reveals that increasing the size of the pillars increases the wetted diameter of the droplet in both configurations. Theoretical models developed using the Cassie–Baxter and Wenzel states for the radially increasing and radially decreasing pitches satisfactorily predict the experimental behaviors.

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Revisited Cassie's law to incorporate microstructural capillary effects

Cited by 7 publications

References 40 publications

Dependency of Contact Angles on Three-Phase Contact Line: A Review

Dependency of Contact Angles on Three-Phase Contact Line: A Review

Generating Multistructured Ultrasound via Bioinspired Metaskin Patterning for Low‐Threshold and Contactless Control of Living Organisms

Wetting Dynamics of a Water Droplet on Micropillar Surfaces with Radially Varying Pitches

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