NONEQUILIBRIUM DOMAIN GROWTH IN FATTY-ACID ETHYL-ESTER MONOLAYERS

A variety of nonequilibrium growth structures is observed in fatty aci d ethyl ester monolayers. In these monolayers, two different condensed phases exist: one with tilted chains and the other with erected chain s. The formation of the domains of these phases from the fluid phase g ives rise to completely different shapes under non-equilibrium. In the phase with tilted chains, a dendritic growth regime exists in ethyl s tearate monolayers for intermediate compression rates. The arms of the dendrite have a tip-oscillating morphology. At extremely high compres sion rates the tips are no longer stable and the growth does not follo w crystallographic directions. For the shorter chain (ethyl palmitate) the dendritic growth regime is not observed in the phase with tilted chains at low temperatures. Here the domain wall only becomes unstable at extremely high compression rates and the morphology is then fracta l-like. However, at temperatures T > 20 degrees C a dendritic growth r egime occurs. The nonequilibrium structures in both ethyl stearate and ethyl palmitate monolayers are transformed into a circular equilibriu m shape for the condensed phase with tilted chains during a few minute s. In ethyl palmitate monolayers, a phase with erected chains forms du ring the first-order phase transition at temperatures T > 26 degrees C . In this phase the nonequilibrium structures are quite stable and tra nsform very slowly into a compact shape. Even at extremely low compres sion rates branched structures occur. An increase of the compression r ate causes a continuous change from a more dendritic shape to one whic h is quite similar to the dense-branching morphology.