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SYB: Symposium Polymere und kleine Moleküle an Grenzflächen

SYB 5: Polymere und kleine Moleküle an flüssigen Grenzflächen

SYB 5.10: Poster

Tuesday, March 10, 1998, 18:00–20:00, P1

Condensed Phases of Branched Phospholipid Monolayers — •S. Leporatti, F. Bringezu, G. Weidemann, G. Brezesinski, and H. M"ohwald — Max-Planck-Institut f"ur Kolloid- und Grenzfl"achenforschung Rudower Chaussee 5, 12489 Berlin

Branched-chain phospholipid provide interesting model system for the study of the interplay between the polar head group region and hydrophobic chains. Therefore triple chain and quadruple chain phospholipid monolayers have been investigated on water and solid substrates by isotherm measurement, Grazing Incidence Diffraction (GIXD), Brewster Angle Microscopy (BAM) and Scanning Force Microscopy (SFM). GIXD measurement reveal a phase transition from a centered rectangular lattice with chains tilted in a symmetry direction towards nearest neighbours (NN) to a hexagonal unit cell with upright oriented molecules at higher lateral pressure. BAM images show the presence of inhomogeneities resulting from unoccupied areas. SFM (Contact and Tapping Mode) measurements performed at room temperature on monolayers transferred by the LB technique on different substrates (mica, glass and silicon wafers) confirm the presence of defects and holes probably due to electrostatic repulsion between condensed phase domains. Number and size of holes decrease upon compression, and film reorganization is clearly revealed.