DOMAIN FORMATION IN MONOLAYERS

For phospholipids at the air/water interface we demonstrate that molec ular chirality in same, but not in all, cases influences the domain sh apes. In other cases chirality in the head group region can cause a ch iral structure considering the tail arrangement. This indicates head g roup ordering. Minute changes of the molecular structure may change do main morphology from circular to dendritic. This can be related to sli ght changes of the lattice structure. In case of a dendritic domain th e chains are more tilted, the deviation from hexagonal symmetry is mor e pronounced, and hence the lattice anisotropy is larger. This can be understood also in view of recent simulations considering diffusion-li mited aggregation models. In experiments at the oil/water interface we show that the electrostatic repulsion between domains is reduced by e xchanging air against oil. Also line tension is reduced which can be u nderstood by means of simple molecular models. The oil may penetrate i nto domains of the ordered phase if it is aliphatic and exhibits the s ame chain length as the lipid. In other cases it is excluded from the ordered monolayer regions. Taking aliphatic dioles as the most simple models we show that head group chirality is expressed in domain shapes , and partly also in lattice structure.