Two-dimensional surface properties of 2-methoxy ethyl oleate at the air/water interface

Abstract

Methoxy ethyl oleate, a nonionic surfactant, has been investigated at the air/water interface for various surface properties by employing the Langmuir film balance technique. The ester forms an expanded isotherm at the air/water interface. The minimum area of packing (A₀), initial area of increase of surface pressure (A_i), collapse pressure (π_c), and area/molecule at collapse pressure (A_c) have been estimated from the isotherm curve. The higher compressibility coefficient (K) suggests that the ester forms a more expanded liquid film than the parent oleic acid. Besides, the ester film is fairly stable as suggested by only about 30% loss in area over a period of 20 min. The relaxation rates of the ester film at different surface pressures of 10, 15, and 20 mN.m^-1 have been estimated from changes in the surface area/molecule with time. Interestingly, the surface area (54.2 Ų/molecule) that corresponds to a minimized structure projected for the ester, calculated theoretically, agrees reasonably well with the experimental value (57.2 Ų/molecule).