Preparation and stabilization of silver colloids in aqueous surfactant solutions

Silver colloids were prepared in the presence of various surfactants by the reduction of silver nitrate with hydrazine. Because of the positively charged hydrophobic nature of Ag nanoparticles, the Ag colloids prepared in aqueous surfactant solutions of sodium dodecyl sulfate (SDS) and Tween 20 showed good stability. But poor colloidal stability was observed in solutions of cetyltrimethylammonium bromide (CTAB) and NP-9. The stabilization of Ag colloids by surfactant molecules was explained on the basis of the electrostatic interaction between the Ag particles and surfactants and a stabilization model was proposed. The particle size distribution was investigated by ultraviolet (UV) absorption spectroscopy measurements. The UV absorption spectra showed different patterns depending on the nature of the stabilizers (i.e., surfactants). In the case of Tween 20 as a stabilizer, the smallest particles, about 11.6 nm in average diameter, were obtained. In the case of CTAB, pearl formation was observed because of the formation of relatively large particles about 300 nm in size.