Demixing Transition in a Quasi-Two-Dimensional Surface-Frozen Layer

Sloutskin, Eli; Gang, Oleg; Kraack, H.; Ocko, B. M.; Sirota, E. B.; Deutsch, Moshe

doi:10.1103/physrevlett.89.065501

Cited by 11 publications

(10 citation statements)

References 37 publications

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“…The application of the present X-ray methods to the surfaces of binary mixtures of different-n members of our homologous RTIL series should also be illuminating, particularly in comparison with the growing body of bulk (79,80) and surface (81) studies on RTIL mixtures. Tuning the chain length difference in mixtures could drive the system from homogeneity to phase separation, induce different bulk and surface phases, and nucleate surface phases having no bulk counterparts, as found in other systems (82,83). Finally, quantitative theoretical studies elucidating, for example, the roles of the various interactions and molecular conformations in the surface structure and its n evolution, and other related issues, are also much desired.…”

Section: Discussionmentioning

confidence: 99%

Surface structure evolution in a homologous series of ionic liquids

Haddad

Pontoni

Murphy

et al. 2018

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

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Interfaces of room temperature ionic liquids (RTILs) are important for both applications and basic science and are therefore intensely studied. However, the evolution of their interface structure with the cation's alkyl chain length [Formula: see text] from Coulomb to van der Waals interaction domination has not yet been studied for even a single broad homologous RTIL series. We present here such a study of the liquid-air interface for [Formula: see text], using angstrom-resolution X-ray methods. For [Formula: see text], a typical "simple liquid" monotonic surface-normal electron density profile [Formula: see text] is obtained, like those of water and organic solvents. For [Formula: see text], increasingly more pronounced nanoscale self-segregation of the molecules' charged moieties and apolar chains yields surface layering with alternating regions of headgroups and chains. The layering decays into the bulk over a few, to a few tens, of nanometers. The layering periods and decay lengths, their linear [Formula: see text] dependence, and slopes are discussed within two models, one with partial-chain interdigitation and the other with liquid-like chains. No surface-parallel long-range order is found within the surface layer. For [Formula: see text], a different surface phase is observed above melting. Our results also impact general liquid-phase issues like supramolecular self-aggregation and bulk-surface structure relations.

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Section: Discussionmentioning

confidence: 99%

Surface structure evolution in a homologous series of ionic liquids

Haddad

Pontoni

Murphy

et al. 2018

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

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“…Figure 4(b) shows the (n, T) phase diagram. The measured T s n of the monolayer phase (squares, n 17) can be explained by the simple thermodynamical theory of SF used for alkane mixtures [24]. The liquid LGF is treated as an ideal mixture, with a free energy including only the pure components' free energies and the mixing entropy.…”

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confidence: 99%

“…The solid phase of close-packed, extended chains is treated as a strictly regular mixture, with a free energy including also a CTAB-alkane interaction term. Equating the corresponding chemical potentials at T s for each component [24] yields…”

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confidence: 99%

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Wetting, Mixing, and Phase Transitions in Langmuir-Gibbs Films

et al. 2007

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Millimolar bulk concentrations of the surfactant cetyltrimethylammonium bromide (CTAB) induce spreading of alkanes, H(CH(2))(n)H (denoted C(n)) 12< or =n< or =21, on the water surface, which is not otherwise wet by these alkanes. The novel Langmuir-Gibbs film (LGF) formed is a liquidlike monolayer comprising both alkanes and CTAB tails. Upon cooling, an ordering transition occurs, yielding a hexagonally packed, quasi-2D crystal. For 11< or =n< or =17 this surface-frozen LGF is a crystalline monolayer. For 18< or =n< or =21 the LGF is a bilayer with a crystalline, pure-alkane, upper monolayer, and a liquidlike lower monolayer. The phase diagram and film structure were determined by x-ray, ellipsometry, and surface tension measurements. A thermodynamic theory accounts quantitatively for the observations.

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“…Various analytical methods have been employed to characterize thin-layer materials, such as highresolution X-ray diffraction (HRXRD) [ force microscopy (AFM) [2,3], reflection highenergy electron diffraction (RHEED) [4][5][6][7] and glancing-incidence X-ray analysis (GIXA) [8,9]. Among these methods, GIXA is a powerful tool in that it cannot only measure the reflectivity curves, but can also provide quantitative analysis of the layer thickness and the surface/interface roughness.…”

Section: Introductionmentioning

confidence: 99%