INFLUENCE OF THE SPREADING SOLVENT ON THE PROPERTIES OF MONOLAYERS AT THE AIR-WATER-INTERFACE

The influence of the spreading solvents ethanol, hexane, and chloroform on the properties of monolayers of long-chain alcohols, hexadecanoic acid, hexadecanoic acid esters, and L-alpha-dipalmitoylphosphatidylcholine is investigated by surface pressure/area and surface potential/area isotherms, gas chromatography, surface viscosity measurements, spreading velocity measurements, and external infrared reflection-absorption spectroscopy. It is shown that the spreading solvent ethanol and mixtures containing ethanol cause film loss into the subphase, but on the other hand enforce a higher conformational order of the film-forming molecules of 1-hexadecanol monolayers and thus a higher surface viscosity. Ethanol solved in the subphase, however, does not influence the properties of the monolayer up to a concentration of about 1 mL/L. Different surface viscosity values are observed for monolayers spread from chloroform and hexane. The differences between the three spreading solvents are attributed to different spreading kinetics, which result in a different morphology of the monolayers. Infrared spectroscopic investigations do not supply any evidence of solvent molecules embedded in the monolayer.