This proposal relates to the structural studies of Di-stearoyl and di-palmitoyl Polyethylene glycol derivates as a function of the PEG head group at the air-water and the oil-water interfaces. These surfactants are currently being studied as an aid to intestinal adsorption of drugs after an oral administration. In a future experiment the interfacial structure of a lipid monolayer in the presence of these surfactants at the important oil-water interface will be investigated to understand the increase in membrane permeability as a result of added surfactants.