Influence of molecular weight of PVP on aggregation and thermal diffusivity of silver-based nanofluids

With the aim of preparing stable nanofluids for heat exchange applications and to study the effect of surfactant on the aggregation of nanoparticles and thermal diffusivity, stable silver colloids were synthesized in water by a green method, reducing AgNO3 with fructose in the presence of poly-vinylpyrollidone (PVP) of various molecular weights. A silver nanopowder was precipitated from the colloids and redispersed at 4 vol% in deionized water. The Ag colloids were characterized by UV-Visible spectroscopy, combined Dynamic Light Scattering and ?-potential measurements, Laser Flash Thermal Diffusivity. The Ag nanopowders were characterized by Scanning Electron Microscopy and Thermal Gravimetric Analysis. It has been found that the molecular weight of PVP strongly affects the ?-potential and the aggregation of nanoparticles, and thereby affecting the thermal diffusivity of the obtained colloids. A maximum improvement of thermal diffusivity by about 10 % was found for nanofluids prepared with PVP having higher molecular weight.