Silver nanoparticles were synthesized in water-in-oil microemulsion using sodium bis(2-ethyl- hexyl)sulfosuccinate (AOT) as a surfactant, silver nitrate solubilized in the water core of one microemulsion as a source of silver ions, hydrazine hydrate solubilized in the water core of the other microemulsion as a reducing agent. Ultraviolet-visible spectrum was used for confirming the formation of silver nanoparticles and evaluating the effect of continuous phases. Transmission electron microscopy (TEM) was also used for elucidating the structure of the resultant particles. TEM micrographs confirm that the nanoparticles prepared in AOT-cyclohexane microemulsion are all spherical with mean diameters of 5.10 nm and standard deviation of 2.84 nm. The effect of various continuous phases in the microemullsion, such as hexane, heptane, octane, cyclohexane and dodecane, on the formation of silver nanoparticles was investigated. On increasing the chain length of alkanes, the exchange rate coefficient increases, that is to say, the exchange rate between reverse micelles increases. As a result, the average diameter of the silver nanoparticles decreases correspondingly. Comparing to the microemulsion formed in alkanes with short chain lengths and cyclohexane, the plasma resonance of silver sol prepared in AOT-dodecane microemulsion has the broadest absorption peak, indicating that the average size of the particles formed in this microemulsion is smaller than that of the particles formed in other microemulsions. The micelles formed in AOT-cyclohexane microemulsion have a special interfacial rigidity, and thus the formation rate of silver nucleation decreases remarkably. As a result, the growth of the silver nanocrystals may be incomplete and the plasma resonance of the silver nanoparticles displays an absorption peak with a lower absorption intensity and broader absorption band.

Key words: silver nanoparticles, sodium bis(2-ethylhexyl)sulfosuccinate, microemulsion, continuous phase