SURFACE-PROPERTIES AND MISCIBILITY OF MONOLAYERS OF DIMYRISTOYLPHOSPHATIDYLCHOLINE AND POLY(ETHYLENE OXIDE) LIPIDS AT THE WATER AIR INTERFACE/

The miscibility of dimyristoylphosphatidylcholine (DMPC) and poly(ethy lene oxide) lipids (PEG lipids) in monolayers has been assessed throug h surface pressure and surface potential measurements. These experimen ts performed under equilibrium conditions at constant area revealed a strong dependence of the interfacial behavior of these mixtures on the polymer chain length. While for the lipid with the short PEO chain co mposed of 5 monomer units the mixtures with DMPC displayed almost an i deal behavior, for longer PEO chains (13 and 31 monomer units) pi-delt a isotherms considerably deviated from ideality. The effect of hydroca rbon and polymer chain orientation and of the structuring of interfaci al water induced by PEO lipids on their mixing behavior with DMPC and on calculated effective dipole moments is discussed and analyzed.