Coexistence of phases in monolayers of branched-chain phospholipids investigated by scanning force microscopy

The coexistence of phases in multiple-chain phospholipid monolayers is reve aled after both horizontal ('scooping up or Langmuir-Schaefer-Kato techniqu e) and vertical (Langmuir-Blodgett technique (LB)) transfer onto mica subst rates by means of scanning force microscopy (SFM) in tapping and contact mo de experiments. Both methods show similar surface topography features. Brew ster angle microscopy (BAM) experiments display the formation of round-shap ed and dendritic domains in the coexistence region between liquid-condensed (LC) and liquid-expanded (LE) phases in monolayers at the air/water-interf ace. Higher resolution SFM on samples transferred from this region indicate the presence of defects inside the larger domains and the formation of sma ller aggregates and stripes in the surrounding background. The measurements produce direct proof of a substrate-mediated condensation during/after the transfer. The main difference between the two dipping modes used is the el ongation of the small aggregates in the case of vertical transfer. Horizont al deposition appears to better preserve shape and size of the domains. (C) 2000 Elsevier Science B.V. All rights reserved.