ISOTHERM AND X-RAY-DIFFRACTION STUDIES OF MIXED MONOLAYERS

We have studied Langmuir monolayers of saturated fatty acid-alcohol mi xtures (same chain length) and acid-acid mixtures (different chain len gth) using isotherms and X-ray diffraction. The diffraction data confi rm that the constituents are miscible, and that at zero pressure the m ixed acid-alcohol monolayer areas are less than the areas of the pure components. We have determined the phase diagrams of a number of diffe rent mixtures. In any given phase, the intermolecular distances measur ed perpendicular to the molecules are independent of the pressure and of the constituents of the mixture. However, the location of some phas e boundaries is a strong function of the composition of the mixture.