Depth profiling of small molecules in dry latex films by confocal Raman spectroscopy

The distribution of small molecules in dry latex films is the result of dri ving forces competing to displace these molecules at the interfaces or to r etain them distributed inside the film. In order to provide a better insigh t into the process leading to segregation of surfactant molecules, confocal Raman spectroscopy was used. This technique was powerful in the quantitati ve determination of the distribution profiles of small molecules, namely so dium dodecyl sulfate (SDS) and sulfate anion (SO42-), active in Raman mode, in the overall thickness of polymeric films. The concentration of the SO42 - ion is higher at the film/substrate interface than in the bulk whereas th e film/air interface exhibits a depletion, which propagates at 50 mu m from the surface in the film thickness. An enrichment of SDS is found at both i nterfaces; and aggregates of small molecules inside the film were detected for both SO42- and SDS. (C) 2000 Elsevier Science Ltd. All rights reserved.