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The behavior of Langmuir monolayers of saturated and unsaturated C18 triglycerides (TAGs) was studied as two-dimensional (2D) models for paint systems, at the air-water interface or transferred onto solid films. The organization of saturated tristearin (C18:0) monolayer was probed thanks to grazing incidence X-ray diffraction: one observes a hexagonal packing of the chains perpendicular to the air-water interface, in contrast to what is described in the literature. Conversely, the mono-and poly-unsaturated TAGs (triolein C18:1, trilinolein C18:2 and trilinolenin C18:3) monolayers do not present any organization at the air-water interface but do exhibit peculiar reactivity regarding the air atmosphere. The obtained results derived from the evolution of surface pressure -molecular area isotherms and monolayers compressibility under different atmospheres over time, combined with ultrahigh-vacuum infrared (UHV-FTIR) spectroscopy, showed the adsorption of O 2 molecules in the monolayer together with chemical reactions with hydrocarbon chains. The kinetic effect of lead ions, known to be efficient siccative agents in oil paints, was also assessed: the addition of Pb 2+ in the subphase induces an increase of the O 2 adsorption.

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