POLYMERIZATION OF A DIACETYLENIC PHOSPHOLIPID MONOLAYER AT THE AIR-WATER-INTERFACE

Monolayers of a polymerizable phospholipid on water have been studied both before and after polymerization. Before polymerization, the phase diagram is established by isotherm measurements and optical microscop y (epifluorescence and direct observation between crossed polarizer an d analyzer). This allows us to bring into evidence a coexistence regio n between a condensed and an expanded phase, above a triple point temp erature T(t) = 20-degrees-C. The dramatic influence of impurities on t he size of coexistence domains between the condensed phase and the exp anded one is clearly demonstrated, even at a very low concentration of impurities. Structural and morphological modifications during the pol ymerization were investigated using X-ray surface scattering together with atomic force microscopy. Whatever the polymerization conditions ( constant area or constant pressure), X-ray reflectivity clearly shows the reorientation of the diacetylenic links. Only constant area polyme rization leads to a viscoelastic behavior of the film, as shown by tal cum decoration. The topochemical nature of the polymerization of diace tylenic groups induces strong constraints on the monolayers and, when the polymerization is achieved at constant area, leads to the collapse of the films evidenced by both techniques.