Interfacial Films and Wetting Behavior of the Air/Hexadecane/Aqueous Solution of a Surfactant System

Abstract

The tension of the three interfaces and the dihedral angle of the lens of the air/hexadecane lens/aqueous solution of tetramethylammonium dodecyl sulfate (TMADS) system were measured as a function of the surfactant concentration. The air/water surface tension vs concentration curves both with and without an oil lens exhibited a break point corresponding to the phase transition of the adsorbed films. From the thermodynamic analysis, it was shown that the phase transition drives the spreading of hexadecane molecules into the adsorbed film. The dihedral angle decreased very rapidly from about 50°at zero concentration to about 6°at the phase transition point and then increased slowly to about 20°at the critical micelle concentration (cmc), suggesting the very drastic change in wetting properties at the phase transition point. The plausible gap was observed between the dihedral angles measured and those calculated from the interfacial tension values at the concentration range from just above the phase transition to near the cmc. This suggests a case where the Neumann relation does not hold even when a lens exists stably. One of the possibilities may be that the wetting film is rather thick just above the phase transition point.

Adhesion to the hydrocarbon phase increases phenanthrene degradation by Pseudomonas fluorescens LP6a

“…The surface and interfacial tension measurements of deionized water were comparable to previous literature values (Aratono et al 2001;Dorobantu et al 2004). Surface and interfacial tensions of uninoculated TSB and spent cell-free TSB medium were slightly lower than this control in the absence of 1-dodecanol.…”

Wetting of Surfactant Solutions by Alkanes

“…[16,17] The first unambiguous evidence for a wetting transition in alkanes on surfactant solutions was provided by Aratono and co-workers, who measure the surface tension of varying concentrations of tetramethylammonium dodecylsulfate (TMADS) solutions in contact with a reservoir of hexadecane. [18] The firstorder nature of the wetting transition was confirmed for hexadecane on DTAB solutions by ellipsometry. [19] Herein, we have explored the generality of the wetting behaviour of alkanes on surfactant solutions.…”

“…Since the hydrocarbon chains of the surfactant interact more strongly with oil than with air, K ow @ K aw , [18] and the spreading coefficient increases linearly (i.e., becomes less negative) with increasing m. Substituting Equation (4) in Equation (3) and retaining only the leading term in m we obtain after some algebra (for the case…”

Thermodynamics of Formation of and Adsorption at Interfaces with a Floating Lens

“…Furthermore, in our next papers, the equations in Section 4.2 for four-component systems will be applied to the results for the interfacial tension of the air/hexane solution of an oil-soluble fluorocarbon substance/water and those for the air/hexadecane/aqueous solution of a surfactant with a floating hexadecane lens (20,21).…”

“…In the course of this, we employ the H convention and introduce newly the P convention in order to define the surface excess thermodynamic quantities unequivocally and then claim that the P convention brings in a kind of thickness of a reference lens phase in the interfacial region. Second, the equations are simplified so as to be applicable to the experimental systems such as the air/long-chain alcohol/ water with an alcohol lens (12), the air/oil solution of oilsoluble long-chain alcohol/water with an oil solution lens (20), and air/oil/aqueous solution of a surfactant with an oil lens (21), where the effect of curvatures of the interfaces seems to be not so influential for a lens in our usual experiments.…”