In order to design composite membranes which would be able to present a high selectivity to CO2, a novel amphiphile N-(2-aminoethyl) trans-9-octadecenamide was synthesized from trans-9-octadecenoic acid and ethylenediamine. Its structure was confirmed by mass and NMR spectroscopies. Monolayers of this amphiphile were formed at the air/water interface and studied by recording surface pressure/area isotherms. Langmuir-Blodgett films were also prepared and characterized by IR spectroscopy.