DISTRIBUTION OF SURFACTANTS IN LATEX FILMS

The distribution of four surfactants, namely sodium dodecyl sulfate (SDS), hexadecyl trimethylammonium (or cetyltrimethylammonium) bromide (HTAB), hexadecylpyridinium chloride (HPCl), ethoxylated nonyl phenol containing 10 or 25 ethoxy groups (NP10 and NP25), in poly(2-ethylhexyl methacrylate) (P2EHMA) latex films was studied by Fourier transform infrared (FTIR) spectroscopy (transmission and attenuated total reflection (ATR)) as a function of time, total surfactant concentration and film formation conditions. The distribution is established during the drying period of the latex and then evolves slowly in the dry film owing to the incompatibility of the surfactant with the polymeric medium. The interfaces, film-air and film-support, can be enriched or deficient in surfactant. In the interpretation of the results, three levels of analysis can be distinguished. The first is purely phenomenological, an intermediate level analysis goes within the film formation process and discusses the fate of the surfactant in this context, and the third is the most fundamental level, at which the importance of the polymer-surfactant interactions clearly appears. Lines of research are proposed for further improvement of the understanding of the surfactant distribution in latex films.