Determination of the solid surface tensions

León, Vladimir; Tusa, Alfonso; Araujo, Yani Carolina

doi:10.1016/s0927-7757(99)00020-5

Cited by 13 publications

(3 citation statements)

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“…Thus, in this study, solubility is estimated by the modified Flory−Huggins theory, which accounts for the membrane elasticity. The Flory−Huggins interaction parameter is evaluated from the polar acid−base surface tension components obtained from the contact angle goniometry using the standard probe liquids. − For a laboratory cast cellulose acetate (CA) membrane without a support layer, direct measurement of the solubility was possible and was found to be in good agreement with the estimated value, as discussed later in Table .…”

Section: Introductionmentioning

confidence: 93%

Pervaporation from a Dense Membrane: Roles of Permeant−Membrane Interactions, Kelvin Effect, and Membrane Swelling

et al. 2004

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Dense polymeric membranes with extremely small pores in the form of free volume are used widely in the pervaporative separation of liquid mixtures. The membrane permeation of a component followed by its vaporization on the opposite face is governed by the solubility and downstream pressure. We measured the evaporative flux of pure methanol and 2-propanol using dense membranes with different free volumes and different affinities (wettabilities and solubilities) for the permeant. Interestingly, the evaporative flux for different membranes vanished substantially (10-75%) below the equilibrium vapor pressure in the bulk. The discrepancy was larger for a smaller pore size and for more wettable membranes (higher positive spreading coefficients). This observation, which cannot be explained by the existing (mostly solution-diffusion type) models ofpervaporation, suggests an important role for the membrane-permeant interactions in nanopores that can lower the equilibrium vapor pressure. The pore sizes, as estimated from the positron annihilation, ranged from 0.2 to 0.6 nm for the dry membranes. Solubilities of methanol in different composite membranes were estimated from the Flory-Huggins theory. The interaction parameter was obtained from the surface properties measured by the contact angle goniometry in conjunction with the acid-base theory of polar surface interactions. For the membranes examined, the increase in the "wet" pore volume due to membrane swelling correlates almost linearly with the solubility of methanol in these membranes. Indeed, the observations are found to be consistent with the lowering of the equilibrium vapor pressure on the basis of the Kelvin equation. Thus, a higher solubility or selectivity of a membrane also implies stronger permeant-membrane interactions and a greater retention of the permeant by the membrane, thus decreasing its evaporative flux. This observation has important implications for the interpretation of existing experiments and in the separation of liquid mixtures by pervaporation.

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Section: Introductionmentioning

confidence: 93%

Pervaporation from a Dense Membrane: Roles of Permeant−Membrane Interactions, Kelvin Effect, and Membrane Swelling

et al. 2004

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“…Increasing E reduces the water production and therefore favors the drying of the electrode, which in turn reduces the proton conductivity. This dewetting is facilitated by CrN, which is hydrophobic in comparison to Pt, [43][44][45][46] and sheds enough water to empty electrode pores to the degree that ionic contact to some parts of the catalyst is lost under low water production condi-tions. We use the term "drying" here in a relative sense, not intended to mean completely dry because the reactants are fully humidified and some water is still being produced.…”

Section: Resultsmentioning

confidence: 99%

“…This can be attributed to hydrophilic Pt, which has a reported contact angle with water of zero. 43 However, we expect two-phase electrodes that employ nonmetallic hydrophobic materials to exhibit incomplete flooding, and the fraction of the pores that are filled with water is likely a function of operating conditions, particularly the current density, which directly correlates to water production. The reported water contact angle for sputter-deposited CrN ranges from 80 to 100°at room temperature 44,45 and 79-88°at 70°C.…”

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confidence: 99%

Sputter-Deposited Pt/CrN Nanoparticle PEM Fuel Cell Cathodes: Limited Proton Conductivity Through Electrode Dewetting

Gasda

Eisman

Gall

2010

J. Electrochem. Soc.

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Platinum-coated chromium nitride electrodes are deposited onto gas diffusion layers by normal and glancing angle deposition and are tested as cathodes for proton exchange membrane ͑PEM͒ fuel cells. X-ray diffraction and scanning electron microscopy show that the CrN forms 111-oriented nanoparticles with ͕100͖ facets that are covered by 3.4 ϫ 10 11 Pt mounds/cm 2 , independent of Pt loading 0.05 to 0.25 mg/cm 2 . Polarization curves exhibit dE/d͑log i͒ slopes b Ϸ −100 and Ϫ150 mV/dec for high ͑E Ͼ 0.75 V͒ and low ͑E Ͻ 0.5 V͒ potentials, respectively, but show an anomalous drop with b Ϸ −420 mV/dec in the intermediate voltage range. This is attributed to poor proton conduction associated with a reversible dewetting of electrode pores during low current operation. Quantitative analyses of rate-dependent polarization curves and electrochemical impedance spectra show that the time scale for pore filling by process water is 10 3 s, and that the ionic resistance R C within the electrode increases by a factor of 4, from R C Ϸ 0.2 to 0.8 ⍀ cm 2 , as E increases from 0.5 to 0.8 V. The increasing electrode resistance is attributed to a low water production rate at low current, which allows the relatively hydrophobic CrN to expel water from the electrode pores, resulting in a higher resistance for ionic transport. These results show that even ultrathin sputtered catalyst layers can exhibit incomplete flooding.Proton exchange membrane ͑PEM͒ fuel cells hold much promise for portable and automotive applications due to their high conversion efficiency and power density. 1 One obstacle to the widespread commercialization of fuel cells is the high cost of the platinum catalyst. Therefore, much effort is devoted to replacing or reducing the Pt loading w. 2 Most of today's commercial fuel cells minimize w by using a network of 30-50 nm wide carbon particles that support 2-5 nm wide Pt nanoparticles. 3,4 A challenge associated with this Pt/C approach is a decreasing efficiency and limited lifetime due to sintering and growth of the Pt, 5 peroxide attack of the membrane, 6 and carbon corrosion. 7 Moreover, some reports suggest that the lower limit in reducing Pt loading in this approach has already been reached, as reducing w to below 0.40 and 0.05 mg/cm 2 for cathode and anode, respectively, decreases the output efficiency. 8,9 Considerable efforts have been directed at replacing the precious metal catalyst with other less costly materials. One possible material is CrN, which has a lower activity than Pt, 10 but is an attractive candidate to supplement or replace Pt in lower cost fuel cell electrodes because of its well-known wear and corrosion resistance. 11 Industrial CrN coatings are most commonly deposited by reactive magnetron sputtering. Sputter deposition has also gained interest for Pt catalyst deposition, 2,12-17 as it provides a pathway to fabricate very low Pt loading ͑w = 0.005 mg/cm 2 ͒ 18 electrodes with a high degree of control and reproducibility. We have recently reported that sputtering Pt from highly oblique incide...

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Interfacial interaction of bio-leaching of pyrite mineral

Wang

Suo

et al. 2008

J. Cent. South Univ. Technol.

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Electrokinetic and contact angle measurements were used to discuss the interfacial interaction on bio-leaching of pyrite mineral. Surface energy parameters of pyrite mineral and thiobacillus ferrooxidans were obtained by calculating according to formula of Young's equation and contact angle measurements. The results show that surface energy of thiobacillus ferrooxidans is much higher than that of pyrite mineral, and the reaction of pyrite mineral with thiobacillus ferrooxidans causes the reduction of the pyrite surface energy. The interfacial interaction energies between pyrite mineral and thiobacillus ferrooxidans were also obtained based on polar interfacial interaction theory and electrokinetic and contact angle measurements. The thermodynamics approach only considering Lifshitz-van der Waals and Lewis acid-base interaction fails to explain the adhesion behavior of the bacteria, but the extended Derjaguin-Landan-Verwey-Overbeek theory concerning Lifshitz-van der Waals and Lewis acid-base and the electrostatic can exactly predict interfacial interaction.

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Determination of the solid surface tensions

Cited by 13 publications

References 10 publications

Pervaporation from a Dense Membrane: Roles of Permeant−Membrane Interactions, Kelvin Effect, and Membrane Swelling

Pervaporation from a Dense Membrane: Roles of Permeant−Membrane Interactions, Kelvin Effect, and Membrane Swelling

Sputter-Deposited Pt/CrN Nanoparticle PEM Fuel Cell Cathodes: Limited Proton Conductivity Through Electrode Dewetting

Interfacial interaction of bio-leaching of pyrite mineral

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