CONFOCAL MICRO-RAMAN SPECTROSCOPY OF BLACK SOAP FILMS

Black soap films from aqueous solutions of sodium dodecyl sulphate are studied by micro-Raman confocal spectroscopy. At the end of the drain ing process films of different thicknesses are obtained depending on t he experimental conditions: Working in a closed humidified chamber len ds to common black films while, under evaporation or in the presence o f electrolyte, Newton black films an observed. From the Raman spectra of these films, quantitative information is deduced about the conforma tional and lateral order of the aliphatic surfactant chains. as well a s the thickness of the residual water layer, More accurate measurement s of the thickness of these ultimate films have been carried out by tr ansmission ellipsometry and their effective refractive index measured by Brewster angle reflectivity. The thinner films present higher molec ular organization and their aqueous con exhibits unusual spectral feat ures. (C) 1998 A,American Institute of Physics. [S0021-9606(98)01602-X ].