Thickness and organization of black films using confocal micro-Raman spectroscopy

Ultrathin and self-supported films of sodium dodecyl sulfate (SDS) constituted of two surfactant monolayers separated by an interstitial layer of water have been studied using a confocal micro-Raman spectrometer. It appears to be very convenient to follow the draining of water and later on to characterize the final equilibrium state of the film with thicknesses ranging from 100 to less than 50 Angstrom, depending on the experimental conditions. In spite of, the very weak Raman signal emitted by these films (less than 1 count/s), it is shown that it is possible to obtain well defined spectra and consequently to draw direct and quantitative information on the residual amount of water and about the conformational and lateral order of the aliphatic surfactant chains. (C) 2000 Elsevier Science B.V. All rights reserved.