Surfactant Effects on Dispersion Characteristics of Copper-Based Nanofluids: A Dynamic Light Scattering Study

We present a study of powder agglomeration and thermal conductivity in copper-based nanofluids. Synthesis of the copper powders was achieved by the use of three different surfactants (polyvinylpyrrolidone, oleic acid, and cetyl trimethylarnmonium bromide). After careful determination of morphology and purity, we systematically and rigorously compared all three of the surfactants for the production of viable copper-based nanofluids using dynamic light scattering. Our results show that the use of surfactants during synthesis of copper nanopowders has important consequences on the dispersion of the powders in a base fluid. The oleic-acid-prepared powders consisted of small particles of similar to 100 nm that did not change with the addition of dispersant. The CTAB-prepared powders exhibited the best dispersion characteristics, as they formed small particles of approximately 80 nm in the presence of SDBS. The thermal conductivity enhancement in our nanofluids exhibited a linear relationship with powder loading for an average particle size of similar to 100 nm and similar particle size distributions that range from similar to 50 to 650 nm, but independent of crystallite size and with all other factors maintained constant (surface area, surface additives, levels of oxidation) such that a 0.55 vol % loading results in a thermal conductivity enhancement of 22% over water and a 1.0 vol % loading results in a thermal conductivity enhancement of 48% over water. This study is the first to decouple the effect of a carefully characterized particle size distribution using dynamic light scattering versus crystallite size from X-ray line broadening on the thermal conductivity enhancement of a nanofluid.