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 interfacial behavior of six structurally different poly(oxyethylene) (POE)-based polymer surfactants at the air-water interface. On a pure water subphase the surfactants have collapse surface pressures dependent on the POE chain length. The surfactant monolayers collapse at well-determined surface pressures, and the lower POE chain-length surfactants collapse at higher pressures than those with high POE content. This difference vanishes as increasing amounts of salt are added to the subphase. The PiA-isotherms are smooth, which is normal for polymeric surfactants. A closer analysis of the isotherms reveals characteristic behavior that can be attributed to structural differences. Similarities in thermodynamic behavior suggest that the molecular orientation is the same despite the structural differences. A new expression for the compressibility factor is developed to explain the relationship between this parameter and surface pressure for polymeric monolayers. Copyright 1999 Academic Press.

NMR Self-Diffusion Studies of the Water and the Oil Components in a W/O/W Emulsion

The application of the pulsed field gradient NMR technique to a double emulsion is presented. This method determines the diffusion behavior of the different components of the emulsion. The details of the system studied, which is of the W/O/W type, have been taken from the literature. Information obtained pertains to the size distribution of the water droplets in both the starting emulsion and the double emulsion. In addition, the different phenomena that govern the oil diffusion in both systems have been identified and discussed.