Surfactant-Induced Surface Freezing at the Alkane-Water Interface

Abstract

Long-chain alkanes exhibit surface freezing at the alkane-air but not the alkane-water interface. Ellipsometry and surface tensiometry are used to show that a simple cationic surfactant, hexadecyltrimethylammonium bromide (CTAB), can induce surface freezing at the tetradecane-water interface even when present in mole fractions as low as 0.1. The surface-freezing temperature T(s) is a linear function of the interfacial excess of CTAB. The excess surface entropy below T(s), S(sigma)=-0.76+/-0.02 mJ K-1 m(-2), is consistent with a rotator phase. Ellipsometry provides strong evidence for a frozen monolayer in which the chains are oriented near the surface normal.

Solid–liquid phase transition in a Gibbs monolayer of melissic acid at the n-hexane–water interface

“…The possibility of such a phase transition at an alkanewater interface has been discussed for a long time [3,4,5,6,7]. The observation of a solid -liquid phase transition at the n-hexane -water interface in the Gibbs monolayer of a surfactant is reported in this work.…”

Diffuse X-ray scattering near a two-dimensional solid–liquid phase transition at the n-hexane–water interface

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AbstractAccording to experimental data on X-ray scattering and reflectometry with the use of synchrotron radiation, a two-dimensional crystallization phase transition in a monolayer of melissic acid at the n-hexane -water interface with a decrease in the temperature occurs after a wetting transition.The observation of a two-dimensional solid -liquid phase transition at the oil -water interface was reported in [1,2,3]. In this work, the temperature dependence of the intensity of diffuse (nonspecular) scattering of 15-keV photons at the n-hexane -water interface, where such a transition occurs in the adsorbed layer of melissic acid (C 30 -acid) [3], is studied.

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“…The observation of a two-dimensional solid -liquid phase transition at the oil -water interface was reported in [1,2,3]. In this work, the temperature dependence of the intensity of diffuse (nonspecular) scattering of 15-keV photons at the n-hexane -water interface, where such a transition occurs in the adsorbed layer of melissic acid (C 30 -acid) [3], is studied.…”

Faraday Instability in a Surface-Frozen Liquid

“…The abrupt onset of SF at T s allows one to switch on (and off) the solid phase by a small temperature variation. Understanding such interfaces would also elucidate the role of flow in nucleation and growth processes of crystals from melts, which are dominated by such interfaces [6].SF occurs in melts of several chain molecules (alkenes, alcohols, semi-fluorinated alkanes, diols, C i E j ) [7], and at both liquid/liquid [8] and liquid/solid [9] interfaces. Related surface ordering effects were observed in melts of polymers comprising alkyl chains in the backbone or as side chains [10], in liquid alloys [11], and in several liquid crystals [12].…”

“…SF occurs in melts of several chain molecules (alkenes, alcohols, semi-fluorinated alkanes, diols, C i E j ) [7], and at both liquid/liquid [8] and liquid/solid [9] interfaces. Related surface ordering effects were observed in melts of polymers comprising alkyl chains in the backbone or as side chains [10], in liquid alloys [11], and in several liquid crystals [12].…”