Monolayers of some poly(oxyethylene)-based surfactants at the air-water interface: The effect of structural variations and salt concentration

The Langmuir surface balance technique has been used to study the interfaci al behavior of six structurally different poly(oxyethylene) (POE)-based pol ymer surfactants at the air-water interface. On a pure water subphase the s urfactants have collapse surface pressures dependent on the POE chain lengt h, The surfactant monolayers collapse at well-determined surface pressures, and the lower POE chain-length surfactants collapse at higher pressures th an those with high POE content, This difference vanishes as increasing amou nts of salt are added to the subphase, The IIA-isotherms are smooth, which is normal for polymeric surfactants, A closer analysis of the isotherms rev eals characteristic behavior that can be attributed to structural differenc es. Similarities in thermodynamic behavior suggest that the molecular orien tation is the same despite the structural differences. A new expression for the compressibility factor is developed to explain the relationship betwee n this parameter and surface pressure for polymeric monolayers. (C) 1999 Ac ademic Press.