Impact of Bulk Phase Transitions and Wetting Transitions on Adsorption Isotherms in Binary Systems in Contact with Solid

Hamraoui, Ahmed; Privat, Mireille

doi:10.1006/jcis.1998.5542

Cited by 4 publications

(9 citation statements)

References 14 publications

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“…Adsorption Isotherms. All adsorption isotherms of diluted aqueous solutions of 2,4,6-TMP or 2,5-DMP on silica were achieved through the gravimetric method. , Each sample used for both isotherm determination and NMR experiments was prepared from a diluted solution of known concentration. It is worth noting that, to get reproducible results, the mixing of both species needs to be very good in order to have a “true” solution.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Adsorption of the water−2,5-dimethylpyridine (2,5-DMP or 2,5-lutidine) liquid binary mixture on amorphous silica (Aerosil type) has been a subject of focus within our laboratory for many years. The water−2,5-DMP liquid system exhibits a lower consolute point at T C = 13.1 °C and X C = 27 wt %; this strongly affects surface behavior, especially adsorption, and this effect is more and more marked as the solubility limit and critical point are approached. − In these studies, we pointed out that adsorption isotherms in diluted aqueous phase exhibit some very significant features:…”

Section: Introductionmentioning

confidence: 97%

“…The water-2,5-DMP liquid system exhibits a lower consolute point at T C ) 13.1 °C and X C ) 27 wt %; this strongly affects surface behavior, especially adsorption, and this effect is more and more marked as the solubility limit and critical point are approached. [3][4][5] In these studies, we pointed out that adsorption isotherms in diluted aqueous phase exhibit some very significant features:…”

Section: Introductionmentioning

confidence: 99%

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Adsorption Mechanism of Substituted Pyridines on Silica Suspensions: An NMR Study

et al. 2004

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Adsorption isotherms of 2,5-dimethylpyridine (2,5-DMP) on Aerosil 200 silica from water-2,5-DMP binary mixtures are known to exhibit special features indicative of surface phase transitions in the adsorbed layer. We have made similar observations on another substituted pyridine, 2,4,6-trimethylpyridine (2,4,6-TMP). By using 1D and 2D NMR spectroscopy, we investigated adsorbed layers on silica in suspension in water/substituted-pyridine mixtures and demonstrated the existence of adsorbed species specific signals. Comparison of signals with those displayed on NMR spectra of liquid binary mixtures under various pH conditions rules out adsorption via interaction of the surface silanol group and the lone electron pair of the nitrogen atom. A mechanism of adsorption through the interaction of surface siloxane oxygen and the aromatic pi-system is proposed; it is consistent with both thermodynamic measurements and stacking of substituted pyridines within the adsorbed layer.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Adsorption Mechanism of Substituted Pyridines on Silica Suspensions: An NMR Study

et al. 2004

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“…Frequently, these investigations have been carried out by ellipsometry. For water-2, 5 DMP mixtures against a silica wall, our studies included adsorption behaviour along the coexistence curve [19]; their results will be described below.…”

Section: Theoretical Aspects: General Features Of Adsorption Behaviou...mentioning

confidence: 99%

“…Given the temperature 0 0.5 ; T e and T f are the boiling point and the fusion point of pure water respectively; T c is the critical temperature for the 2ϕ system; T α w and T v w are the wetting temperatures for the two-liquid-phase system against silica and vapour, respectively [20,21]. Curve 1 is the hypothetical prewetting line against vapour; it should start at T v w tangentially to the coexistence curve; curve 2 is the already established prewetting line against silica [18,19], starting at T α w . Curve 2 is close to the γ -branch because γ is the non-wetting phase against silica.…”

Section: Phase Equilibriamentioning

confidence: 99%

Critical and wetting transitional adsorption behaviour in a liquid system against vapour and other walls

Huruguen¹,

Amara²,

Méar³

et al. 2001

J. Phys.: Condens. Matter

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The adsorption of 2, 5 DMP (2, 5-dimethylpyridine) at the free surface of water (1)-2, 5 DMP (2) liquid mixtures was determined from surface tension and activity measurements. Two divergences were found: the former was observed at Tc for the critical isochore and the 2, 5 DMP-rich γ-phase which, at coexistence, completely wets the surface at Tc, whereas the latter was noticed at Tw for the water-rich β-phase. These results were compared with those found under similar conditions for the same liquid system with silica as the wall; this comparison is quite fruitful because, with silica, the preferentially wetting phase is the β-phase.

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Wetting transitions

Bonn¹,

Ross²

2001

Rep. Prog. Phys.

360

398

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When a liquid droplet is put onto a surface, two situations distinguishable by the contact angle may result. If the contact angle is zero, the droplet spreads across the surface, a situation referred to as complete wetting. On the other hand, if the contact angle is between 0 • and 180 • , the droplet does not spread, a situation called partial wetting. A wetting transition is a surface phase transition from partial wetting to complete wetting. We review the key experimental findings on this transition, together with simple theoretical models that account for the experiments.The wetting transition is generally first order (discontinuous), implying a discontinuity in the first derivative of the surface free energy. In this case, if one measures the thickness of the adsorbed film beside the droplet, at the wetting transition a discontinuous jump in film thickness occurs from a microscopically thin to a thick film. We show that this can lead to the observation of metastable surface states and an accompanying hysteresis. The observed hysteresis poses, in turn, a number of questions concerning the nucleation of wetting films that we also consider here. In addition, we consider the equilibrium wetting film thickness that results from a competition between the long-range van der Waals forces and gravity.Finally, the first-order character of the wetting transition can lead to a similar transition even when the phase that does the wetting is not (yet) stable in the bulk. For such prewetting transitions, a discontinuous thin-to-thick film transition occurs off bulk coexistence. We show that, for the large variety of systems for which prewetting transitions have been observed, the behaviour is surprisingly uniform, and can be mapped onto a simple generic phase diagram.The second part of the review deals with the exceptions to the first-order nature of the wetting transition. Two different types of continuous or critical wetting transition have been reported, for which a discontinuity in a higher derivative of the surface free energy occurs. This consequently leads to a continuous divergence of the film thickness. The first type is the so-called long-range critical wetting transition, which is due to the long-range van der Waals forces. We show under what circumstances such a transition can occur, and that it is usually preceded by a first-order wetting transition, which however is not achieved completely. This leads to the existence of an intermediate wetting state, in which droplets coexist with a relatively-but not macroscopically-thick film. The second type of transition is the shortrange critical wetting transition, for which the layer thickness diverges continuously from a

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Impact of Bulk Phase Transitions and Wetting Transitions on Adsorption Isotherms in Binary Systems in Contact with Solid

Cited by 4 publications

References 14 publications

Adsorption Mechanism of Substituted Pyridines on Silica Suspensions: An NMR Study

Adsorption Mechanism of Substituted Pyridines on Silica Suspensions: An NMR Study

Critical and wetting transitional adsorption behaviour in a liquid system against vapour and other walls

Wetting transitions

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