Interfacial studies of essential oil—water systems
, Jean Pierre Benoita,
and Curt Thiesc
a Physico-Chimie des Surfaces et Innovation en Pharmacotechnie, UA CNRS 1218, Centre d'Etudes Pharmaceutiques, 5 rue Jean-Baptiste Clément, 92296 Châtenay-Malabry France
b Laboratoire de Chimie des Arômes, Faculté des Sciences, Université de Nice France
c Biological Transport Laboratory, Washington University, St. Louis, MO U.S.A.
Received 17 November 1987; accepted 27 June 1988. Available online 18 January 2002.
The surface tension of mint, lemon and orange oils and the interfacial tension of these oils against water were investigated by the Wilhelmy plate method. Variation of these tensions as well as variation of the surface tension of waters after prolonged contact with the oils were measured as a function of time and temperature. Spreading coefficients Sow calculated from these data show that the spreading tendency of these oils, in the temperature range 30–50°C, is in the order: orange oil> lemon oil> mint oil.
Combined gas chromatography and mass spectroscopy analytical data reveal a high concentration of mint oil constituents in water equilibrated with this oil. Adsorption of these surface-active species at the air/water interface considerably lowers its surface tension. Positive temperature coefficients of the surface tension of this water and of the mint oil/water interfacial tension are attributed to the change in chemical composition occurring at these interfaces during heating.
Lowering of the interfacial tension at orange oil and lemon oil/water interfaces was observed when these interfaces were heated. This may be attributed to the interfacial adsorption of 8-p-menthene-1,2-diol present in the waters equilibrated with orange and lemon oils.
The data obtained may be indicative of phenomena observed during encapsulation of these essential oils by the complex coacervation procedure.