Film formation from concentrated reactive silicone emulsions. 2. Surfactant distribution

Drying mechanisms of concentrated, reactive poly(dimethylsiloxane) in, wate r emulsions, stabilized by a nonionic polyethoxylated fatty alcohol, were s tudied in part I of this series. Upon drying, these emulsions form cross-li nked polymeric films. The present paper focuses on the fate of the surfacta nt during and after film formation, studied by attenuated total reflectance (ATR) and infrared microscopy. The effects of various parameters were inve stigated, namely thickness of the cast layer, surfactant concentration, pre sence of a CaCO3 filler, and aging of the film after drying. The concentrat ion profile of the surfactant in the film shortly after drying presents a d epleted layer on top, a flat vertical line in the bulk, and a strongly enri ched layer in contact with the substrate. The vertical line corresponds in fact to an average over surfactant aggregates with a seemingly very high si ze polydispersity. Drying and coalescence mechanisms have a major influence on the surfactant distribution. In the dry film, the distribution is unsta ble and, upon aging, both film-air and film-substrate interfaces are progre ssively enriched with surfactant. More details on the structure of the film after drying are given in part 3 of this series.