Wetting Transition Characteristics on Microstructured Hydrophobic Surfaces

Lee, Jae Bong; Gwon, Hyuk Rok; Lee, Seong Hyuk; Cho, Minhaeng

doi:10.2320/matertrans.m2010118

Cited by 38 publications

(28 citation statements)

References 24 publications

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“…With this amount of liquid, θ * was found to not depend on the size of the droplet. Bigger droplets should however be avoided, because they alter the measurements of the surface tension , . This phenomenon is likely to result from the interaction of the droplet with the surface roughness.…”

Section: Methodsmentioning

confidence: 99%

Sliding Angle Characterization of Physicochemical and Roughness Changes of GDL Surfaces after Fuel Cell Operation

et al. 2018

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The effect of proton exchange membrane fuel cell (PEMFC) operation on physicochemical properties and roughness of gas diffusion layers (GDL) was evaluated in this work. In addition to static contact angle measurements commonly used for GDLs, sliding angle measurements were also performed on a membrane electrode assembly (MEA) both new and used in service within commercial PEMFC. These latter revealed significant changes after 4,000 h in service that were not detectable with the static counterparts. The main novelty of this study is to correlate the contact and sliding angle measurements and to combine them with various modeling approaches developed for modeled surfaces. After 4,000 h of aging, it was thus shown that the surface of the GDLs became more hydrophilic, contrary to the roughness, which remains unchanged.

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Section: Methodsmentioning

confidence: 99%

Sliding Angle Characterization of Physicochemical and Roughness Changes of GDL Surfaces after Fuel Cell Operation

et al. 2018

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“…Stage 1 is the sub-process during which the bending depth of meniscus between four pillars changes from h x2 to h x1 , namely, the TPCL on pillars moves downwards from x=H-h x2 to x=H-h x1 (figures 1 A3 to A4). Stage 2 means the sub- Because the contact angle of the TPCL on posts keeps unchanged advancing contact angle during the two stages, R 1 and h x1 will also keep unchanging according to the equations (8) and (9). But the solid-liquid interface below the droplet increases continuously until the entire substrate below the drop is completely wetted.…”

Section: ) Qualitative Descriptionmentioning

confidence: 97%

Mechanism Study on Transition of Cassie Droplets to Wenzel State after Meniscus Touching Substrate of Pillars

Liu

et al. 2017

J. Phys. Chem. C

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To understand the conditions and mechanism of droplet wetting transition from Cassie to Wenzel state (C-W) and furthermore to prohibit this transition are the key research contents about super-hydrophobic materials. In this study, the C-W transition process after meniscus touching substrate (MTS) was divided into different stages. Then, the changes of droplet interfacial free energy (IFE) after MTS were analyzed. And the resistance on three-phase contact line (TPCL) was also investigated. Furthermore, based on the droplet IFE always changing from high to low, a criterion formula for C-W transition was derived so that the mathematical model was founded. The calculation results show that the smaller the pitch and/or diameter of pillars, the more difficult the MTS and C-W transition for an initial sessile Cassie droplet. Therefore, nano textures can efficiently prevent the C-W transition. Besides, the MTS of droplets on short and high pillars can be realized with sag and TPCL depinning impalement respectively. Additionally, the greater the intrinsic contact angle, the more unfavorable the droplet C-W transition. Moreover, micro-nano two-tier textures can effectively inhibit the C-W transition. Finally, the model results are in good agreement with the experimental measurements reported in literatures, with 92% accuracy.

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“…At velocities greater than v min the pressure exerted by the impact in the shock envelope (Field, 1999) is enough to force liquid to fill and wet the inside of the gaps between the particles completely, forming a Wenzel state (Wenzel, 1936), as depicted in Figure 5(b). It is the transition between Cassie‐Baxter and Wenzel states that occurs at the rebound‐to‐pinning transition velocity (Lee et al ., 2010). In our system, as the diameter of the hydrophobic glass spheres increased, the depth of the gaps between features increased.…”

Section: Resultsmentioning

confidence: 99%

Transitions of water‐drop impact behaviour on hydrophobic and hydrophilic particles

Hamlett

Atherton

Shirtcliffe

et al. 2013

European J Soil Science

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SummaryExtreme soil water repellency can have substantial implications for soil hydrology, plant growth and erosion, including enhanced splash erosion caused by raindrop impact. Previous studies of water droplet impact behaviour on man-made super-hydrophobic surfaces, with which water-repellent soil shares similar characteristics, revealed three distinct modes of splash behaviour (rebound, pinning and fragmentation) distinguished by two transition velocities: rebound-to-pinning (v min ) and pinning-tofragmentation (v*). By using high-speed videography of single water droplet impacts we show that splash behaviour is influenced by the hydrophobicity of immobile particles, with hydrophobic glass spheres exhibiting all three modes of splash behaviour in the hydrophobic state but hydrophilic spheres exhibiting solely pinning behaviour. We found that increasing the particle size of fixed glass spheres increases vmin. A study of droplet impact on hydrophobic sand shows that the increased roughness of the immobile particles makes impacting droplets more likely to fragment at slower impact velocities. The mobility of the particles influenced droplet impact behaviour, with loose, hydrophobic particles displaying significantly greater v min values than their fixed analogues. The surface tension of the water droplet also lifted loose, hydrophobic particles from the surface, forming highly mobile 'liquid marbles'. Water-repellent soil was also shown to form 'liquid marbles' at both the slow (approximately 0.3-2.1 m s −1 ) and fast (about 7 m s −1 ) droplet impact velocities studied. The observation of very mobile liquid marbles upon water droplet impact on water-repellent soil is significant as this provided a mechanism that may enhance erosion rates of water-repellent soil.3

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Wetting Transition Characteristics on Microstructured Hydrophobic Surfaces

Cited by 38 publications

References 24 publications

Sliding Angle Characterization of Physicochemical and Roughness Changes of GDL Surfaces after Fuel Cell Operation

Sliding Angle Characterization of Physicochemical and Roughness Changes of GDL Surfaces after Fuel Cell Operation

Mechanism Study on Transition of Cassie Droplets to Wenzel State after Meniscus Touching Substrate of Pillars

Transitions of water‐drop impact behaviour on hydrophobic and hydrophilic particles

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