PHASE-DIAGRAM OF LANGMUIR MONOLAYERS OF PENTADECANOIC ACID - QUANTITATIVE COMPARISON OF SURFACE PRESSURE AND FLUORESCENCE MICROSCOPY RESULTS

The phase behavior of Langmuir monolayers of pentadecanoic acid has been investigated by measurements of surface pressure-area isotherms and by fluorescence microscopy. The two techniques are in quantitative agreement and allow the phase boundaries between the gas (G), liquid expanded (LE), and liquid condensed (LC) phases to be determined with precision. The LE-LC and LE-G transitions are first-order. The corresponding critical temperatures, if any, are higher than 37°C for the LE-LC transition and 70°C for the LE-G transition. 0022-3654/90/2094-4588$02.50/0 © 1990 American Chemical Society.