On the Necessity of Using Activities in the Gibbs Equation

Strey, R.; Viisanen, Y.; Aratono, Makoto; Kratohvil, J. P.; Yin, Qiyi; Friberg, Stig E.

doi:10.1021/jp990306w

Cited by 108 publications

(144 citation statements)

References 8 publications

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“…In particular, the surface tension of aqueous ethanol solutions has been experimentally measured many times, with one of the earliest data sets being obtained by Bircumshaw [40] and employed by Guggenheim and Adam [41] in their analysis of the Gibbs adsorption equation. In the present study, we selected the accurate and extensive surface tension measurements at 298.15 K of Aratono et al [42] taken from the table given in Strey et al [43] Thermo-physical data of the pure components from various sources are presented in Table 1 and molar masses were calculated by using IUPAC 1995 atomic weights of the elements. [48] The surface-tension data of aqueous ethanol consists of values for 31 different mole fractions, among which 20 data points were determined at ethanol mole fractions between 0.0010 and 0.1102.…”

Section: Molar Surface Areas Of Pure Liquid Substances In Monolayersmentioning

confidence: 99%

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New Thermodynamics for Evaluating the Surface‐phase Enrichment in the Lower Surface Tension Component

Santos¹,

Reis²

2014

ChemPhysChem

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Regarding the surface phase of liquid mixtures as a thermodynamic phase, ideal surface phases are designed so that at fixed bulk-phase composition, real and ideal surface phases have the same chemical composition and identical limiting slopes for the dependence of surface tension on mole fraction. Standard chemical potentials are introduced for surface phase components, and quasi-exact expressions are worked out to compute ideal surface tensions and surface-phase compositions of real liquid mixtures. Guidelines for choosing molecular models to estimate the molar surface area of pure constituents are given. Ideal and excess surface tensions are calculated by using literature data for aqueous ethanol solutions at 298 K. These results show treatment based on Butler's equations grossly overestimate predicted surface tensions, thus leading to lower ethanol content in the surface phase. These inaccuracies are ascribed to the use of molar surface areas in model equations that are too small.

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Section: Molar Surface Areas Of Pure Liquid Substances In Monolayersmentioning

confidence: 99%

“…Consequently, our slope analysis is done exclusively in the water-rich region, aiming to evaluate an experimental value for lim [a] Ref. [43].…”

Section: Molar Surface Areas Of Pure Liquid Substances In Monolayersmentioning

confidence: 99%

New Thermodynamics for Evaluating the Surface‐phase Enrichment in the Lower Surface Tension Component

Santos¹,

Reis²

2014

ChemPhysChem

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“…The surface tension of water/alcohol mixture decreases monotonically with an increase of ethanol content and is equal to about 35 mN m À1 at 30 % vol of ethanol concentration. [39] The surface tension of poly(n-butyl acrylate) is found in the range of 31-34 mN m À1 .…”

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confidence: 99%

Reversible Collapse of Brushlike Macromolecules in Ethanol and Water Vapours as Revealed by Real‐Time Scanning Force Microscopy

Gallyamov

Tartsch

Khokhlov

et al. 2004

Chemistry A European J

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Environment-controlled scanning force microscopy allowed us to study adsorption and desorption of single poly(methacrylate)-graft-poly(n-butyl acrylate) brush molecules on mica in real time. The molecules transform reversibly from a two-dimensional, extended wormlike state to a compact globular state. The dynamics of the conformational transition was sufficiently slow in order to allow its observation by scanning force microscope in real time. The reversible transformation is effected by coadsorption of water or ethanol, the latter introduces the collapse. Adsorbing ethanol and water from the vapour atmosphere results in a change of the surface properties of mica, either favouring adsorption or desorption of the graft polymer. When the extended, tightly adsorbed poly(n-butyl acrylate) brush molecules are exposed to ethanol vapour, the macromolecules swell and contract to form compact globules. Exchanging the ethanol vapour to a humid atmosphere caused the molecules to extend again to a wormlike two-dimensional conformation. Coexistence of collapsed and extended strands within the same molecule indicates a single-molecule first-order transition in agreement with observations on Langmuir films previously reported.

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“…but close to it. 7 Experimental results reported in the literature seem to show in several cases a discrepancy between surface excess determined directly and via the Gibbs equation.…”

Section: Discussionmentioning

confidence: 99%

Activity of surface active substances determined from their surface excess

Andersson

Krebs

Morgner

2005

Phys. Chem. Chem. Phys.

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Commonly, the surface excess is determined from surface tension measurements via the Gibbs equation. This equation relates the activity (chemical potential), the surface excess, and the surface tension. When knowing two out of the three quantities, the third one can be calculated. Unfortunately, in the case of surface active components the concentration is in most cases too low to determine the activity from a measurable change in the bulk properties and thus assumptions are made about the activity coefficients. However, if the surface excess is measured directly and the surface tension is known, the activity can be determined making use of the Gibbs equation. The surface excess is the quantity of a surfactant solution which changes most strongly with the concentration. Thus it is obvious that this procedure should be used to determine activity coefficients of surfactants. One of the few techniques for determining the surface excess directly is neutral impact collision ion scattering spectroscopy (NICISS). With NICISS concentration depth profiles can be measured in the surface near region with a depth resolution of a few angstro¨ms. The surface excess and the activities are investigated here for the system tetrabutylphosphonium bromide (Bu 4 PBr) dissolved in the polar solvent formamide.

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On the Necessity of Using Activities in the Gibbs Equation

Cited by 108 publications

References 8 publications

New Thermodynamics for Evaluating the Surface‐phase Enrichment in the Lower Surface Tension Component

New Thermodynamics for Evaluating the Surface‐phase Enrichment in the Lower Surface Tension Component

Reversible Collapse of Brushlike Macromolecules in Ethanol and Water Vapours as Revealed by Real‐Time Scanning Force Microscopy

Activity of surface active substances determined from their surface excess

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