Wettability Techniques to Monitor the Cleanliness of Surfaces

Birch, William R.; Carré, Alain; Mittal, K. L.

doi:10.1016/b978-081551555-5.50015-0

Cited by 16 publications

(15 citation statements)

References 27 publications

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“…The equilibrium CA can be calculated from the values of the surface tension coefficients: cos θ = (γ S − γ SL )/γ L , where the γ s are the coefficients of the surface tension, with i = S, V and L standing for solid, vapor and liquid, respectively [26]. The nominal equilibrium contact angle for clean glass and water, is listed as zero [47][48][49].…”

Section: Contact Angle and Contact Diametermentioning

confidence: 99%

Evaporation-induced evolution of the capillary force between two grains

2014

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The evolution of capillary forces during evaporation and the corresponding changes in the geometrical characteristics of liquid (water) bridges between two glass spheres with constant separation are examined experimentally. For comparison, the liquid bridges were also tested for mechanical extension (at constant volume). The obtained results reveal substantial differences between the evolution of capillary force due to evaporation and the evolution due to extension of the liquid bridges. During both evaporation and extension, the change of interparticle capillary forces consists in a force decrease to zero either gradually or via rupture of the bridge. At small separations between the grains (short & wide bridges) during evaporation and at large volumes during extension, there is a slight initial increase of force. During evaporation, the capillary force decreases slowly at the beginning of the process and quickly at the end of the process; during extension, the capillary force decreases quickly at the beginning and slowly at the end of the process. Rupture during evaporation of the bridges occurs most abruptly for bridges with wider separations (tall and thin), sometimes occurring after only 25 % of the water volume was evaporated. The evolution (pinning/depinning) of two geometrical characteristics of the bridge, the diameter of the threephase contact line and the "apparent" contact angle at the solid/liquid/gas interface, seem to control the capillary force evolution. The findings are of relevance to the mechanics of unsaturated granular media in the final phase of drying.

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Section: Contact Angle and Contact Diametermentioning

confidence: 99%

Evaporation-induced evolution of the capillary force between two grains

2014

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“…30 This trend has been previously shown for a variety of non-noble metal oxide materials including zirconium dioxide (ZrO 2 ) and titanium dioxide (TiO 2 ), among others, and occurs due to physisorption of hydrocarbons to OH -groups and other energetically favorable sites present on the surface, 17,31 where van-der-Waals and hydrogen bonding are typical 32 but covalent bonding is also possible. 33 The results of the XPS analysis conducted here show that the amount of carbon present on the surface is indeed increasing over time, indicating that hydrocarbons adsorb to the cleaned surface after exposure to air.…”

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confidence: 99%

Effect of hydrocarbon adsorption on the wettability of rare earth oxide ceramics

Preston

Miljkovic

Sack

et al. 2014

Applied Physics Letters

170

123

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Vapor condensation is routinely used as an effective means of transferring heat, with dropwise condensation exhibiting a 5 -7x heat transfer improvement compared to filmwise condensation.However, state-of-the-art techniques to promote dropwise condensation rely on functional hydrophobic coatings, which are often not robust and therefore undesirable for industrial implementation. Natural surface contamination due to hydrocarbon adsorption, particularly on noble metals, has been explored as an alternative approach to realize stable dropwise condensing surfaces. While noble metals are prohibitively expensive, the recent discovery of robust rare earth oxide (REO) hydrophobicity has generated interest for dropwise condensation applications due to material costs approaching 1% of gold; however, the underlying mechanism of REO hydrophobicity remains under debate. In this work, we show through careful experiments and modeling that REO hydrophobicity occurs due to the same hydrocarbon adsorption mechanism seen previously on noble metals. To investigate adsorption dynamics, we studied holmia and ceria REOs, along with control samples of gold and silica, via X-Ray photoelectron spectroscopy (XPS) and dynamic time-resolved contact angle measurements. The contact angle and surface 2 carbon percent started at ≈ 0 on in-situ argon-plasma-cleaned samples and increased asymptotically over time after exposure to laboratory air, with the rare earth oxides displaying hydrophobic (> 90 degrees) advancing contact angle behavior at long times (> 4 days). The results indicate that REOs are in fact hydrophilic when clean, and become hydrophobic due to hydrocarbon adsorption. Furthermore, this study provides insight into how REOs can be used to promote stable dropwise condensation, which is important for the development of enhanced phase change surfaces. However, the longevity of these ultra-thin coatings remains a question due to the lack of extended or accelerated testing to assess mechanical durability and long-term stability. KEYWORDS:An alternative to the direct application of low-surface-energy coatings relies on surface contamination due to energetically favorable hydrocarbon adsorption, particularly on high thermal conductivity noble metals (i.e., gold and silver). 7 These metals are wetting when clean, but reduce their surface energy by adsorbing hydrocarbons from air, enabling dropwise condensation when used as condenser surfaces. The robustness of this approach is welldocumented, with one paper demonstrating continuous dropwise condensation on gold for over five years in a closed system. 8 Unfortunately, the high price of noble metals prohibits this approach in practice.Researchers have recently demonstrated rare earth oxides (REOs) as potential candidates for condenser surface coatings due the their apparent intrinsic hydrophobicity 9 and costs approaching 1% of gold. 10 However, reported contact angles on REOs are inconsistent. 4Advancing contact angles ranging from 17 -134° have been observed, with a study reporting...

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“…The determination of the equilibrium contact angle, described in Young's equation [57], requires very clean experimental conditions and depends on the liquid surface tension, the surface free energy of the solid and the interaction between the solid and liquid materials [56][57][58]. A deviation from the thermodynamic equilibrium condition results in contact angle hysteresis, which is observed by an advancing angle when the solid/liquid contact area increases and a receding angle when the contact area shrinks [56].…”

Section: Contact Angle and Wettabilitymentioning

confidence: 99%

“…Characterization of the physicochemical nature of the surface and of the contaminant(s) helps to understand the fundamental forces that hold or bind the contaminant to the surface [58]. Characterization of the physicochemical nature of the surface and of the contaminant(s) helps to understand the fundamental forces that hold or bind the contaminant to the surface [58].…”

Section: Basic Process and Principles Of Cleaning Surfacesmentioning

confidence: 99%