Thermodynamic studies on adsorption at interfaces

Gibbs Films of Semi-Fluorinated Alkanes at the Surface of Alkane Solutions

“…For F 12 H 16 and F 12 H 14 at T > T f , the density profiles exhibit a weak maximum next to the surface, indicating some adsorption of these semi-fluorinated alkanes. For temperatures T < T f , density profiles with a pronounced maximum, amounting to an electron density…”

“…Binks et al 1,13,14 concluded from an analysis of surface tension data that the tendency of F n H m molecules to be adsorbed at the hydrocarbon/air interface increases with the antipathy between the fluorinated chain and the hydrocarbon solvent, that is, with increasing chain length of the fluorinated block and increasing carbon number of the hydrocarbon solvent. Hayami and Findenegg 15 studied the temperature dependence of the surface tension of F 12 H 16 16 . This study indicated striking similarities in the phase behavior between Gibbs films of F n H m at the hydrocarbon/air interface and Gibbs films of fatty alcohols and related amphiphiles at the water/air 16 and water/oil 17 interfaces.…”

“…Hayami and Findenegg 15 studied the temperature dependence of the surface tension of F 12 H 16 16 . This study indicated striking similarities in the phase behavior between Gibbs films of F n H m at the hydrocarbon/air interface and Gibbs films of fatty alcohols and related amphiphiles at the water/air 16 and water/oil 17 interfaces. In the system F 12 H 16 + hexadecane, a complication arises from the fact that hexadecane exhibits the phenomenon of surface freezing a few Kelvin above the bulk freezing temperature.…”

“…Since the solubility of the semi-fluorinated alkanes in BCH is less than in dodecane, solutions of 1 mmol/kg were used in these measurements. Figure 6 shows R(q z )/ R F (q z ) curves for F 12 H 16 and F 12 H 18 on BCH recorded at temperatures 3 K below and 3 K above the respective phase transition temperature T f . The electron density profiles F e (z) were again derived from the normalized reflectivities R(q z )/R F (q z ) by the model-independent analysis and are shown as an inset in Figure 6.…”

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Adsorbed monolayer phases of semi-fluorinated alkanes F(CF2)12(CH2)mH with m ) 12, 14,16, and 18 (denoted F12Hm) at the free surface of their solutions in H12 and H16 solvents (dodecane, bicyclohexyl, and hexadecane) were studied by surface tension measurements and surface-sensitive X-ray techniques. Solutions in the two H 12 solvents exhibit sharp first-order phase transitions from a gaslike state at high temperature to a condensed state at lower temperatures.

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