Nanoparticles induced micellar growth in sodium oleate wormlike micelles solutions

The rheological behavior of anionic surfactant sodium oleate (NaOA) in the presence of inorganic salt of sodium carbonate (Na2CO3), organic salt of n-Octyltrimethylammonium bromide (OTAB) and nano-sized silica particles (nano SiO2) was studied in detail. Regardless of the surfactant concentration (NaOA), OTAB was stronger than that of Na2CO3 in promoting the rapid growth of NaOA micelles, resulting in higher viscosity of NaOA aqueous solutions. It was found that nano SiO2 nearly not affects solution viscosity in the NaOA/Na2CO3 system. However, results of NaOA/OTAB system in the presence of nano SiO2 show that nano SiO2 promoted wormlike micelles formation and enhanced the bulk viscosity. Simultaneously, the presence of nano SiO2 also facilitated the branched wormlike micelles formation as confirmed by viscosity and cryo-TEM measurements because of the electrostatic interactions between wormlike micelles and nano SiO2.