Monolayers of 1,2,3-propanetriol esters at the air-water interface: two-dimensional phases and miscibility

Abstract

Monolayers of two glycerol esters, 1-monooleoylglycerol and 1-monostearoylglycerol, were studied at the air-water interface in the 15-30 ~ temperature range.From the experimental isotherms (surface pressure vs area and surface potential vs area) the surface phases of the esters were inferred.The miscibility between the two esters was discussed in relationship to the interfacial orientations and distributions and to the surface phases of the esters.The results obtained supported and strengthened the empirical rule on miscibility previously found [1-7], i.e., for non-ionic compounds the same interfacial orientation of the hydrophobic chains is required in order to have bidimensional miscibility between the components.

Surface Rheological Properties of Monostearin and Monoolein Films Spread on the Air−Aqueous Phase Interface

“…The results obtained in this work support and strengthen the empirical rule regarding miscibility previously reported (Gabrielli et al, 1982;Niccolai et al, 1989); i.e., for nonionic compounds, the same interfacial orientation of the hydrophobic chains is required in order to have bidimensional miscibility between the components. This requisite is not fulfilled…”

“…These results can been explained if the lipids are immiscible at the interface, as was deduced from π-A isotherms. In fact, from the small deviations from the additivity rule and the invariance in collapse pressure as a function of the molar ratio, on the one hand (Niccolai et al, 1989;Carrera et al, 1996), and from the variation of equilibrium surface pressure, thermodynamic parameters (free energy, enthalpy, and entropy of the mixed films), and monolayer stability, on the other hand (Carrera et al, 1996), it can be concluded that monostearin and monoolein molecules are immiscible at the interface. That is, the mixed films of these lipids consisted of islands of pure monostearin or pure monoolein molecules, and these islands probably have variable extension and a random distribution (Niccolai et al, 1989).…”

Molecular Explanation for the Abnormal Flux of Material into a Hot Spot in Ester Monolayers

“…By comparing their compression isotherms in the region of the solid phase, we observed that surface pressures shifted to lower values, at constant mean molecular areas, when the temperature increased, i.e., they showed negative pyrobaric coefficients. ,− Compression isotherms for EA and BS at different temperatures, which were not previously reported, are shown in Figure S3. Despite that negative pyrobaric coefficients have been reported before for ester compounds, ,− to the best of our knowledge, this is the first time they are analyzed in depth, and that a structure-based explanation is proposed for its negative sign. Interestingly, the structurally related compounds, fatty alcohols, and fatty acids form monolayers with positive pyrobaric coefficients. , …”

Structural Characteristics of Monopalmitin Monolayers Spread on Aqueous Sugar Solutions

“…4 to 6) for the liquid-expanded structure, considering the monolayer as a unitary fluid. These equations have provided good results in analogous systems studied by other authors (7,10,19,26,28,29),…”