Stability and Aggregation Kinetics of Silver Nanoparticles in Water in Oil Microemulsions of Cetyltrimethylammonium Bromide and Triton X-100

Abstract

Water in oil (W/O) microemulsions are simple preparative route for nanoparticles where water droplets dispersed in oil stabilized by surfactant or surfactant and cosurfactant monolayer act as nanoreactors to carry out chemical reactions. In this work, silver nanoparticles (AgNPs) were prepared in W/O microemulsions of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX-100) by using AgNO₃ and NaBH₄ as a precursor salt and reducing agent, respectively. To prepare microemulsions, CTAB or TX-100, 1-pentanol, cyclohexane and water were mixed with different molar ratio. AgNPs were prepared with different [AgNO₃] in microemulsions of CTAB with fixed water to surfactant ratio (W_o). Average particle sizes were determined from dynamic light scattering (DLS) measurements. AgNPs prepared from microemulsions of CTAB were unstable while from TX-100, NPs were stable. Aggregation kinetics was investigated by measuring the absorbance at definite time intervals at the absorption maximum, ?_max of AgNPs in different media under pseudo-first-order conditions. The aggregation behavior was studied at different [AgNO₃]:[NaBH₄] and W_o and the parameters were optimized to ensure formation of stable AgNPs without aggregation in microemulsions. This would help tuning the size, stability, and aggregation kinetics of AgNPs by controlling the nature of the surfactant and composition of the microemulsions.