THE SEGREGATION OF SURFACTANT UPON FILM FORMATION OF LATEX DISPERSIONS - AN INVESTIGATION BY ENERGY-FILTERING TRANSMISSION ELECTRON-MICROSCOPY

We investigated the local distribution of emulsifier in dried films ca st from latex dispersions. Energy filtering transmission electron micr oscopy (EFTEM) allowed the detection of heteroatom-containing domains in unstained samples by electron spectroscopic imaging and elemental m apping. If the samples were prepared at temperatures above the minimum film-forming temperature (MFT), separated domains of surfactant were observed in detachment replicas and ultrathin sections. If the prepara tion was carried out below MFT the emulsifier was retained at the part icle surface and similar observations could not be made. It is suggest ed that the mobility of the emulsifier at the surface of the particles is increased upon deformation and coalescence in the process of him f ormation, and that this mobility is a prerequisite for its segregation . Both processes do not take place upon drying below MFT, owing to low er mobility. The correlation between the process of film formation and the segregation of surfactant is discussed for both a dispersion of p oly(vinylacetate) and one of polyacrylate.