Tuning the thermal diffusivity of silver based nanofluids by controlling nanoparticle aggregation

Abstract

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 re-dispersed at 4 vol% in deionized water. The Ag colloids were characterized by UV-visible spectroscopy, combined dynamic light scattering and ζ-potential measurements, and laser flash thermal diffusivity. The Ag nanopowders were characterized by scanning electron microscopy and thermal gravimetric analysis. It was found that the molecular weight of PVP strongly affects the ζ-potential and the aggregation of nanoparticles, thereby affecting the thermal diffusivity of the obtained colloids. In particular, it was observed that on increasing the molecular weight of PVP the absolute value of the ζ-potential is reduced, leading to increased aggregation of nanoparticles. A clear relation was identified between thermal diffusivity and aggregation, showing higher thermal diffusivity for nanofluids having higher aggregation. A maximum improvement of thermal diffusivity by about 12% was found for nanofluids prepared with PVP having higher molecular weight.

Thermal Wavelength Measurement of Nanofluid in an Optical-Fiber Thermal Wave Cavity Technique to Determine the Thermal Diffusivity

“…A maximum enhancement of thermal diffusivity by about 17% was found for Ag nanofluid prepared under only 20 s irradiation times. It has a similar increasing trend to other results which obtained Ag/water nanofluid by using a laser flash photoacoustic method [ 26 ]. The results [ 16 ] also recorded the increase in the thermal diffusivity as the particle size decreased.…”

Determination of the Thermal Diffusivity of Plasmonic Nanofluids Containing PVP-Coated Ag Nanoparticles Using Mode-Mismatched Dual-Beam Thermal Lens Technique

“…Our results also show that the thermal lens technique is more suitable for determining the thermal diffusivity of a colloid at extremely low concentrations than the laser flash method [22]. Figure 10 shows the values of the thermal diffusion coefficients for the samples as a function of the concentration of AgNPs.…”

“…PVP-coated AgNPs (AgNP@PVP) were synthesized by adapting the chemical reduction method proposed by Turkevich [26] to produce Au nanoparticles [22]. In this bottom-up method, 75 mL of a 1 mM solution of silver nitrate (AgNO 3 , Synth PA) is heated to boiling point under magnetic stirring.…”

“…Previous works that have reported the thermal diffusivity of AgNF employing the thermal lens technique considered silver nanoparticles (AgNPs) produced by radiation [19,20] and laser ablation [21]. Besides the thermal lens approach, others techniques such as microflash [22] and the photopyroelectric technique [23] have been employed to determine in AgNFs. Envisaging applications of the nanofluids as cooling fluids or in medicine, it is desirable to employ fluids with low viscosity.…”

Matrix metalloproteases inhibition and biocompatibility of gold and platinum nanoparticles

“…For biomedical applications of NPs, there is a crucial need to clarify the behavior of NPs in living systems. The surface charge of NPs facilitates dispersion of these particles in water, and therefore prevents the aggregation of NPs. The surface coating of NPs can improve stability even in biological media and intercellular environments .…”