Nano-sized graphene oxide as sole surfactant in miniemulsion polymerization for nanocomposite synthesis: effect of pH and ionic strength

Miniemulsion polymerization of styrene using AIBN as initiator at 70 °C has been performed with nano-dimensional graphene oxide (GO) sheets as surfactant (no conventional surfactants employed) with a view to exploring the effects of pH and ionic strength (NaCl concentration). The pH value of the emulsion exerted a relatively minor influence on the polymerization, with a somewhat narrower particle size distribution being obtained at pH = 3.2 relative to pH = 2.4 and 5.2. The ionic strength had a more significant effect - the presence of a suitable concentration of NaCl resulted in increased colloidal stability and narrower particle size distribution. The results are explained in terms of the effects of pH on degree of ionization of COOH groups of GO and the influence of ionic strength on the electric double layer, and have implications with regards to synthesis of polymer/graphene nanocomposite materials for a variety of applications.