Star defects, boojums, and cardioid droplet shapes in condensed dimyristoylphosphatidylethanolamine monolayers

The inner texture and shape of condensed droplets in Langmuir monolayers of the phospholipid dimyristoylphosphatidylethanolamine (DMPE) have been studied by Brewster angle microscopy. We report a strong temperature dependence of the inner texture in the range 15 degreesC less than or equal to T less than or equal to 25 degreesC, with continuous distortions and boojums at low temperatures and segmented textures that include 6-fold star defects at high temperatures. Image analysis of metastable in = 1 textures at low temperatures has yielded important material parameters. At all temperatures, a clockwise bend structure of the c-director is observed. Droplet shapes are typically cardioidlike, becoming more circular for small droplets or high temperatures. This system exemplifies the need for better theoretical models to understand the problem of the formation of complex shapes and textures in condensed Langmuir monolayers.