Size and shape-controlled synthesis of silver nanoparticles for high-thermal conductivity nanofluids
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Size and shape-controlled synthesis of silver nanoparticles for high-thermal conductivity nanofluids Glorimar Garcia1, Celia Osorio-Cantillo2 and Oscar Perales-Pérez3 1 University of Puerto Rico, Department of Mechanical Engineering, P.O. Box 9045, Mayagüez, P.R. 00681-9045. 2 University of Puerto Rico, Department of Chemistry, P.O. Box 9019, Mayagüez, P.R. 00681-9045. 3 University of Puerto Rico, Department of Engineering Science and Materials, P.O. Box 9044, Mayagüez, P.R. 00681-9044. ABSTRACT Nanofluids, consisting of nanometric particles suspended in a base fluid, have become a new alternative for improving heat management technology. Silver, which is known to exhibit pretty high electrical and thermal conductivity among metals, has been selected for this research. At present, we are focused on the study of the size- and shape-controlled synthesis conditions of silver nanocrystals in polyol media. Control of crystal size and shape at the nanoscale were achieved by suitable selection of the synthesis conditions and the presence of habit-controlling agents like chloride ions. Silver nanostructures (faceted crystals, wires, rods) were remarkable monodisperse in size and their dimension could be controlled in the 30-50nm range (particles) and 24-127nm in thickness for rods or wires. INTRODUCTION New applications of nanotechnology has targeted the seek for a new type of cooling fluid, so called nanofluids, consisting in the stable suspension of nanometer sized solid particles in conventional refrigerants [1]. Metal nanostructures are promising candidate materials because of the expected increase in thermal conductivity of the corresponding nanofluid in contrast to the base fluid. Furthermore, the size and concentration of the particles in contact with the fluid should also have a significant influence on the corresponding heat transfer capacity. A wide range of investigations has been focused to optimize nanoscale structures under size- and shape controlled synthesis conditions [1-3]. Among metals, silver is a very interesting candidate for nanofluids application because of its morphological features and expected influence on the structural, optical and thermal conductivity behavior of the host fluid. For instance, silver nanostructures such as nanowires or nanorods are proposed for the removal of heat in polymerbased composites used for electronic packaging [3-5]. Regarding to nanofluids for thermal conductivity applications, there is still a gap related to the actual effect of size and shape on the corresponding thermal conductivity. T.Cho et al. used a polyol synthesis where silver nitrate as salt precursor and Poly(acryl-amide-co-acrylic acid) as dispersion stabilizer. Different concentrations of the silver nanofluid (1000 ~10000 ppm) were prepared to thermal conductivity which transient hot wire method was used [6]. Although silver particle size was in the nanometric range, there was no a precise control on the particle shape and its possible influence on the thermal conductivity. Regarding shape-controlled synt
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