Stability properties of water-based gold and silver nanofluids stabilized by cationic gemini surfactants

Well dispersed water-based gold and silver nanofluids were prepared by one-step method. Gemini quaternary ammonium salt surfactants of variable spacer lengths (16-n-16, n = 2, 3, 4, 6, 8) were used to obtain nanofluids with good suspension stability. The effects of pH value on the formation and stability of nanofluids were investigated before and after preparation. The thermal stability of nanofluids were investigated at 140-170 degrees C. The spacer length of the used gemini surfactants capped on the surface of the nanoparticles affects the stability of nanofluids. It indicated that the stability of nanoparticles was related closely to the pH value of the medium and the length of the spacer joining the two cationic ammonium headgroups in gemini surfactants. The gemini surfactant with the shortest spacer (16-2-16) could not stabilize metal nanoparticles well. The nanoparticles stabilized by 16-3-16 were more stable in a wide pH range of the nanofluid systems. The nanoparticles stabilized with 16-8-16 length have better thermal stability. (C) 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.