The temperature dependence of mixed monolayers of poly-γ-methyl- l-glutamate and palmitic acid at the air/water interface

Abstract

There is a flat region (plateau region) ascribed to the transition from monolayer to bilayer in the surface pressure ( F)-area ( A) isotherm of poly-γ-methyl- l-glutamate (PMLG) at the air/water interface. The change in entropy from initial to final state of this transition is very small and negative. This indicates that the order in the monolayer and bilayer states is almost the same but that the former is a little more random. At or below 20°C, the monolayer of palmitic acid (PA) forms a solid condensed film and no difference in the F- A isotherm was detected regardless of temperature. However, there is a break at about 16.8°C in the curve of temperature versus surface pressure of the flat region in the F- A isotherm corresponding to the collapse of the PA monolayer. This suggests that the monolayer states of PA above and below 16.8°C are different. PA at or above 20°C is more miscible with PMLG in the monolayer state than PA at or below 15°C. The difference between miscibility of PMLG in the monolayer state and PA at or above 20°C and at or below 15°C can perhaps be ascribed to the difference between the monolayer states of PA above and below ca. 16.8°C.