Vaporization and layering of alkanols at the oil/water interface

Tikhonov, A. M.; Schlossman, Mark L.

doi:10.1088/0953-8984/19/37/375101

Cited by 29 publications

(42 citation statements)

References 32 publications

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“…The almost-pure alkanol layer formed below T s in that transition in the nonionic alkanol surfactant systems (14,15) is a monolayer for Δn > 6 only, and a multilayer for Δn < 6. In contrast, we observe a mixed surfactant-alkane monolayer for all Δn and T. The monolayer's structure at T < T s also differs greatly in the two systems, comprising partly disordered chains for alkanols (14,15) and extended chains here. A detailed elucidation of the origin of these differences will have to await the availability of a broader set of similar studies for other systems.…”

Section: Discussionmentioning

confidence: 97%

“…Surfactants are often used to modify the hydrophobic interactions in a manner that reduces the interfacial free energy. However, the microscopic structure of surfactant-modified bulk oil-water interfaces, the subject of the present study, has been studied by X-ray methods only for nonionic alkanol surfactants (14,15). X-ray measurements for oil-water interfaces modified by ionic surfactants are not available in the literature.…”

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confidence: 99%

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Modification of deeply buried hydrophobic interfaces by ionic surfactants

Tamam

Pontoni

Sapir

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Hydrophobicity, the spontaneous segregation of oil and water, can be modified by surfactants. The way this modification occurs is studied at the oil-water interface for a range of alkanes and two ionic surfactants. A liquid interfacial monolayer, consisting of a mixture of alkane molecules and surfactant tails, is found. Upon cooling, it freezes at T s , well above the alkane's bulk freezing temperature, T b . The monolayer's phase diagram, derived by surface tensiometry, is accounted for by a mixtures-based theory. The monolayer's structure is measured by high-energy X-ray reflectivity above and below T s . A solid-solid transition in the frozen monolayer, occurring approximately 3°C below T s , is discovered and tentatively suggested to be a rotator-to-crystal transition.H ydrophobicity (1) is abundant in nature and in technology (2). It plays a dominant role in fields ranging from the structure of living matter, like cell membrane stabilization and protein folding, to microemulsion-mediated nanoparticle and quantum dot formation (1,(3)(4)(5)(6)(7). Although the macroscopic phenomenology of hydrophobicity is well studied, its theoretical understanding, particularly on a molecular level, is still incomplete (1,8). Recent progress in X-ray scattering from buried interfaces allowed determination of the structure of hydrophobic interfaces (including the oil-water one) with near-atomic resolution, leading to an animated debate on the molecular-scale origin and manifestations of the hydrophobic interaction (9-13). Surfactants are often used to modify the hydrophobic interactions in a manner that reduces the interfacial free energy. However, the microscopic structure of surfactant-modified bulk oil-water interfaces, the subject of the present study, has been studied by X-ray methods only for nonionic alkanol surfactants (14, 15). X-ray measurements for oil-water interfaces modified by ionic surfactants are not available in the literature. Macroscopic optical measurements have uncovered intriguing interface structure modifications (16), indicating that these more widely used and more complex electrically charged surfactants, which also have bulkier headgroups, may modify the interface differently from the nonionic ones. Thus, a key ingredient in the fundamental understanding of the relation between ionic surfactants and the hydrophobic interaction is still missing.Using X-ray reflectivity (XR) and surface tensiometry, we measured the atomic-resolution structure and thermodynamics of oil-water interfaces decorated by ionic surfactants (see Fig. 1A). Two different interfacial phases are observed. At high temperatures, a liquid interfacial monolayer is found; upon cooling, a frozen monolayer forms at the interface, separating the bulk liquid oil and aqueous phases. We measured the interfacial phase diagram and offer a simple thermodynamic model which fully accounts for the interfacial freezing (IF). At a lower temperature, the frozen monolayer is found to undergo an additional transition to full crystallinity where the m...

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Section: Discussionmentioning

confidence: 97%

mentioning

confidence: 99%

Modification of deeply buried hydrophobic interfaces by ionic surfactants

Tamam

Pontoni

Sapir

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…It was reported earlier [7][8][9] that a surface electrical double layer can form at the n-hexane -water interface owing to adsorption (from hexane solutions) of long-chain molecules of fluorinated alcohols, such as 1,1,2,2-tetrahydroheptadecafluorodecanol (FC 10 OH) and 1,1,2,2-tetrahydrohenicosafluorododecanol (FC 12 OH), or normal alkanols, such as n-tetracosanol (C 24 OH) and n-triacontanol (C 30 OH). The fluorocarbon chain of FC 12 OH is longer by two -CF 2 -units than that of FC 10 OH, and the hydrocarbon chain of C 30 OH is longer by six -CH 2 -units than that of C 24 OH.…”

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confidence: 77%

The critical crossover at the n-hexane-water interface

Tikhonov

2010

J. Exp. Theor. Phys.

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According to estimates of the parameters of the critical crossover in monolayers of long-chain alcohol molecules adsorbed at the n-hexane -water interface, all systems in which this phenomenon is observed are characterized by the same value of the critical exponent ν ≈ 1.8.Atoms or molecules adsorbed on the surface of a liquid or crystal frequently form a spatially inhomogeneous structure in which domains of two homogeneous phases coexist [1][2][3][4]. Both of these phases tend to intermixing, since the formation of one-dimensional interphase boundaries leads to a significant decrease in the system energy [5]. An evident consequence of this is the impossibility of a two-dimensional (2D) first-order phase transition in this system; instead, an infinite sequence of phase transitions (critical crossover) must take place [6].This article presents the results of an analysis of experimental data obtained earlier [7,8], which allowed a critical parameter of the crossover at the n-hexanewater interface to be established.A macroscopically flat interphase boundary (interface) between n-hexane (a nonpolar organic solvent) and water (see Fig. 1) offers an example of the system, featuring the phenomenon of critical crossover. Under normal conditions, n-hexane (saturated hydrocarbon with the formula C 6 H 14 , a density of ∼ 0.65 g/cm 3 at T = 298 K, and a boiling temperature of about 342 K) and water exhibit virtually no mutual solubility. * tikhonov@kapitza.ras.ru 1

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“…For example, at the surface of high-molecular-weight saturated hydrocarbons and monatomic alcohols (their interface with air), there occurs a solidliquid phase transition at a temperature above the bulk melting temperature [33,34]. The observation of two-dimensional solidliquid and liquidgas phase transitions at the oilwater interface has also been reported [32,[35][36][37]. Many authors consider these thermotropic transformations in the context of mono-and bimolecular layer models.…”

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confidence: 99%

Thermotropic phase transition in an adsorbed melissic acid film at the n-hexane–water interface

Tikhonov

2017

Jetp Lett.

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A reversible thermotropic phase transition in an adsorption melissic acid film at the interface between n-hexane and an aqueous solution of potassium hydroxide (pH ≈ 10) is investigated by X-ray reflectometry and diffuse scattering using synchrotron radiation. The experimental data indicate that the interface freezing transition is accompanied not only by the crystallization of the Gibbs monolayer but also by the formation of a planar smectic structure in the 300-Å-thick adsorption film; this structure is formed by 50-Å-thick layers.

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Vaporization and layering of alkanols at the oil/water interface

Cited by 29 publications

References 32 publications

Modification of deeply buried hydrophobic interfaces by ionic surfactants

Modification of deeply buried hydrophobic interfaces by ionic surfactants

The critical crossover at the n-hexane-water interface

Thermotropic phase transition in an adsorbed melissic acid film at the n-hexane–water interface

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