The role of reverse micelles and metal-surfactant interactions in the synthesis of gold ink in reverse emulsions stabilized by AOT, Tergitol NP-4 and Span 80

The development of advanced methods for the synthesis of metal-containing solvent ink is important for 2 and 3D printing as well as for obtaining composites of nanoparticles with hydrophobic polymers. The formation mechanism of gold organosols in reverse emulsions stabilized by the widely used surfactants AOT, Tergitol NP-4 or Span 80 was investigated. It was found that the main factors promoting the successful synthesis are the presence of small size reverse micelles in a dispersion medium and the occurrence of interaction of a surfactant with the complex anion AuCl4–. The interaction provides a rapid transfer of gold ions from the micron size emulsion droplets to nanometer micelles. After that, the micelles play their conventional role of nanoreactors, limiting the growth and stabilizing a nanoparticle during the reduction of AuCl4– by hydrazine. After destruction of the emulsion and separation of the aqueous phase, the sols were subjected to additional electrophoretic concentration. It was demonstrated that the obtained concentrate can be used as the solvent ink to form conductive films and composites of nanoparticles with hydrophobic polymers like polystyrene, where nanoparticles retain the properties of plasmonics. The novelty and significance of the study in terms of colloidal and surface chemistry consist in the fundamental and experimental substantiation of the new and promising application of such a classical colloid as reverse emulsions.