Desorption of Fatty Acids from Monolayers at the Air/Water Interface to β-Cyclodextrin in the Subphase

In this study the cyclodextrin (CD)-induced desorption of fatty acids from monolayers at the air/water interface was examined. Desorption rates were determined while maintaining the monolayer at constant surface pressure. Of the three fatty acids examined (tetra-, penta-, and hexadecanoic acids), tetra- and pentadecanoic acids displayed a liquid-expanded (LE) to liquid-condensed (LC) phase transition at ambient temperature. We examined the effect of the phase transition on desorption rates with pentadecanoic acid monolayers. The cyclodextrin-induced desorption of pentadecanoic acid was a linear function of time (zero-order kinetics) when the monolayer surface pressure was kept constant during the course of the experiments. With different fatty acid monolayers, the desorption rates (with the monolayers in the LC state) were observed to decrease as the fatty acid chain length increased (from 14 to 16 carbons). The desorption rates with pentadecanoic acid monolayers increased curvilinearly with increasing te...