Desorption of emulsifiers from polystyrene latexes studied by various surface techniques: A comparison between XPS, ISS, and static SIMS

The results obtained with three surface spectroscopic methods (XPS, ISS, and static SIMS with quadrupole or time-of-flight analyzers) available for the characterization of the particle surface of polystyrene latexes have been compared. The main point was to quantify the desorption of the surfactants used in the emulsion polymerization (Aerosol MA and sodium dodecylbenzenesulfonate) by the study of both unpurified and purified latexes. A comparison was made between these results and those obtained on a latex prepared by emulsion polymerization without any tensioactive stabilizer, therefore bearing only sulfate groups issued from the initiator. Sodium dodecyl sulfate was used as a reference for the presence of sulfate groups. The pure emulsifiers were also investigated separately. The various samples were analyzed as either powders or films, and the results obtained on films are discussed in terms of the migration of the surfactant toward the interface during the preparation of the films. On the other hand, our results showed clearly that static SIMS with a time-of-flight analyzer is the most suitable technique to study the desorption of emulsifier from latex particles. These results demonstrate that, after extensive purification by mixed-bed ion exchange resins, the strong acid emulsifier (Aerosol MA) can be completely desorbed.