Pattern growth during the liquid expanded-liquid condensed phase transition in langmuir monolayers of myristic acid

Abstract

The nucleation and growth of liquid condensed domains into a continuous liquid expanded phase has been monitored by epifluorescence microscopy in monolayers of myristic acid mixed with a fluorescent dye. Various patterns, ranging from circular droplets to highly ramified structures, have been observed over a temperature range of a few degrees C around room temperature. This reflects the complexity of the phase diagram of myristic acid monolayers. For instance the existence of a critical temperature T _c for the two-phase coexistence region around 31 °C has probably a strong influence on the patterns aspects since the line tension between the liquid expanded and the liquid condensed phases vanishes at T _c . We believe that the morphological unstability of the interfacial front is diffusion-controlled, as first predicted by Mullins and Sekerka in binary alloys for the growth of a solid sphere in a uniformly supersaturated melt. On the other hand, thermal diffusion only a small plays role in the present experiments. In the limit of very small line tension, the patterns are self-similar and are characterized by a Hausdorff exponent of 1.8±0.1.