Measurement of Wenzel roughness factor by laser scanning confocal microscopy

Ai, Hongru; Li, Xiangqin; Shi, Shuyan; Zhang, Ying; Liu, Tianqing

doi:10.1039/c6ra26897h

Cited by 41 publications

(19 citation statements)

References 27 publications

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“…The roughness factor is the ratio of the actual surface area divided by the macroscopically apparent surface area and is thus larger than unity. The roughness factor R usually ranges between 1 and 2 but should not exceed 1/cos θ as cos θ W cannot be larger than 1 . The contact angle on a rough substrate is given by the Wenzel equation

\cos θ_{normalW} = R \cdot \cos θ

…”

Section: Wettability Of (Mof) Surfacesmentioning

confidence: 99%

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Hydrophobic Metal–Organic Frameworks

et al. 2019

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formed from organic ligands and metal cations. [1][2][3][4][5][6][7][8][9][10] They are typically synthesized under mild conditions via coordinationdirected self-assembly processes and are also known as metal-organic coordination networks and porous coordination polymers. [11][12][13][14] Due to their high surface areas, large porosity, tunable pore sizes, and functionalities, MOFs have prospective applications in fields such as gas storage/separation, sensing or recognition, proton conduction, and magnetism. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] However, the advantageous unique structural features of even some of the best-performing MOFs are readily degraded because of their high moisture sensitivity, which may limit their practical applications. [29][30][31][32] Consequently, there is an ongoing search for highly hydrophobic, porous, sorbent materials to be employed in various large-scale applications in industry such as oil spill cleanup, hydrocarbon storage/separation, or water purification. [33][34][35][36][37] Many academics, industrial scientists, and engineers have therefore conducted research on the fabrication of superhydrophobic surfaces, which involves hydrophobic surface modification and creating surface roughness on the micrometer-or nanoscale. Hydrophobic surfaces are defined as substrates with an apparent contact angle greater than 90° with respect to water. On superhydrophobic materials, water droplets have contact angles above 150° and show very low adhesion because the drops partially rest on an air cushion. The surface energy and roughness govern the wettability of hydrophobic surfaces. In general, lower surface energies and higher roughness are associated with larger contact angles, lower contact angle hysteresis, and robust superhydrophobicity. Because of their ultralow surface energies (10-20 mN m −1 ), alkyl-based or fluorinated compounds are commonly used as hydrophobic modifiers to prepare surfaces with high intrinsic contact angles (>90°). [33][34][35][36][37][38][39][40][41][42] Recently, few methods have been developed for synthesizing hydrophobic MOFs including both pristine and composite systems. This review offers a comprehensive overview of the state of the art in hydrophobic MOF synthesis and the field's challenges and opportunities. Various synthetic strategies for preparing hydrophobic MOFs and their composites are introduced. We discuss the basics of wetting and critical challenges in the characterization of these hydrophobic materials. The potential applications of hydrophobic MOFs and related Metal-organic frameworks (MOFs) have diverse potential applications in catalysis, gas storage, separation, and drug delivery because of their nanoscale periodicity, permanent porosity, channel functionalization, and structural diversity. Despite these promising properties, the inherent structural features of even some of the best-performing MOFs make them moisture-sensitive and unstable in aqueous media, limiting their practical usefulness. This problem could be ...

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\cos θ_{normalW} = R \cdot \cos θ

…”

Section: Wettability Of (Mof) Surfacesmentioning

confidence: 99%

“…This becomes even more severe for drop sizes above ≈10 µL where gravity influences the drop's shape. It has recently been shown that contact angles can be measured with greatly improved accuracy using techniques such as laser scanning confocal microscopy . Here, the lower side of the droplet is scanned using a laser.…”

Section: Wettability Of (Mof) Surfacesmentioning

confidence: 99%

Hydrophobic Metal–Organic Frameworks

et al. 2019

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“…In fact, when working with a rough material at micro and submicrometric scale, water drops are not completely adhered to the surface since, topographic heterogeneities condition the way at which drops lie on the surfaces and hence the contact angle. 50 Two models are usually used to describe wettability behavior of solid surfaces, Wenzel 51 and Cassie-Baxter 52 models respectively. Both of them predict an increase of hydrophobicity behavior as micro-heterogeneity increases, which is in accordance with the results obtained in the present work.…”

Section: Resultsmentioning

confidence: 99%

PCL/collagen blends prepared by solution blow spinning as potential materials for skin regeneration

Lorente

Corral

González‐Benito

2021

J of Applied Polymer Sci

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Solution blow spinning (SBS), is used to prepare biocompatible fibrous materials based on poly-ε-caprolactone (PCL), modified with collagen. Materials with different compositions in terms of collagen are prepared. Structure, morphology, topography, wettability behavior, and cytotoxicity are studied in order to investigate the potentiality of these materials for medical applications in the field of tissue repairing and regeneration. Structure is studied by Fourier transformed infrared spectroscopy, morphology by scanning electron microscopy, topography by optical profilometry and wettability behavior by contact angle measurements. The addition of small amounts of collagen to PCL by SBS can induce important variations in the morphology and topography of the materials that, in turns, lead to changes in the wettability behavior and ability of HaCat cells adhesion and proliferation. The analysis of surface characteristics together with the use of a model based on mats constituted by cylinders disposed perpendicularly to each other point out that, under the compositions considered, the main factor leading to higher adhesion and proliferation of cells on the PCL/collagen is the presence of more available surface area.

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“…where A R is the projected area of the rough surface relative to the corresponding area of the smooth flat surface, A S , equivalent to the FOV. This factor has successfully been used to characterize surface roughness in several recent studies (e.g., Ramón-Torregrosa et al, 2008;Bizjak, 2010;Ai et al, 2017). Analysis of variance (ANOVA) performed on the calculated W r values indicated no significant effect due to the different FOVs.…”

Section: Fracture Surface Roughness Measurementsmentioning

confidence: 99%

Rock Fracture Sorptivity as Related to Aperture Width and Surface Roughness

Brabazon

Perfect

Gates

et al. 2019

Vadose Zone Journal

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Core Ideas Spontaneous imbibition was measured in rock fractures using neutron radiography. Early‐time uptake of water displacing air showed a square root of time dependency. Fracture sorptivity was quantified from the slope of the early‐time uptake data. Fracture sorptivity increased with increasing fracture aperture width. Fracture sorptivity decreased with increasing fracture surface roughness. Fractures in low‐porosity rocks can provide conduits for fluid flow. Numerous researchers have investigated fluid flow through fractures under saturated conditions. However, relatively little information exists on spontaneous imbibition in fractures, whereby a wetting fluid displaces a non‐wetting fluid by capillarity. We investigated spontaneous imbibition of water displacing air in a suite of fractured low‐porosity sedimentary and igneous rock cores (5.08‐cm length by 2.54‐cm diameter). Mode I fractures were induced in the cores by compression between opposing parallel flat plates. The following physical properties were measured: bulk density, ρb; solid‐phase density, ρs; porosity, ϕ; contact angle, θe; fracture aperture width, xgeo; and fracture surface roughness, Wr. The wetting front in each fracture was imaged using dynamic neutron radiography. Early‐time uptake exhibited a square root of time dependency, and was quantified by linear regression, with the slope equal to the fracture sorptivity, Sf. Estimates of Sf ranged from 10.1 to 40.5 mm s−0.5, with a median value of 25.0 mm s−0.5. There was a statistically significant effect of rock type on Sf, with igneous rocks generally having lower mean values than sedimentary rocks. Differences in ρb, ρs, ϕ, and θe between the rock types did not contribute significantly to the variation in Sf. However, xgeo and Wr were significantly correlated with Sf. These correlations indicated that Sf increases with increasing xgeo, as predicted by early‐time capillary theory, and decreases with increasing Wr, analogous to the decrease in fracture permeability with increasing surface roughness observed under saturated flow conditions.

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Measurement of Wenzel roughness factor by laser scanning confocal microscopy

Abstract: The Wenzel roughness factor r is one of the most important parameters to characterize a super-hydrophobic surface.

Cited by 41 publications

References 27 publications

Hydrophobic Metal–Organic Frameworks

Hydrophobic Metal–Organic Frameworks

PCL/collagen blends prepared by solution blow spinning as potential materials for skin regeneration

Rock Fracture Sorptivity as Related to Aperture Width and Surface Roughness

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