Compression-rate dependent domain growth patterns in diacetylenic chiral lipids Langmuir films: choline vs. ethanolamine head-groups*

In this talk, we discuss domain growth in Langmuir monolayers of two diacetylenic lipids, one with choline and other with ethanolamine head group. We found that (i) Unlike a diacetylenic lipid, Diyne PE (23:2), the diacetylenic Diyne PC (23:2), does not form chiral hierarchal self-assembled patterns. (ii) Structured solid domains in Diyne PC (23:2) Langmuir layer forms within a lower temperature range than with Diyne PE (23:2). Comparing their domain morphology we argue that choline and ethanolamine head groups interact differently with water, influencing the packing-mode. (iii) For both lipids, the growth patterns depend on the compression speed. At lower compression-rate the condensed domains grow as fractal dendrites with straight backbone whereas at rapid compression rate, domains grow as curved claws developing branches as they grow. Since slow or rapid compression rate pushes the monolayer to different non-equilibrium state (different super-saturation), we reason that solid phase grow out of different metastable states, generating distinct morphology.