Fabrication, characterization, and thermal property evaluation of silver nanofluids

Abstract

Silver nanoparticles were successfully prepared in two different solvents using a microwave heating technique, with various irradiation times. The silver nanoparticles were dispersed in polar liquids (distilled water and ethylene glycol) without any other reducing agent, in the presence of the stabilizer polyvinylpyrrolidone (PVP). The optical properties, thermal properties, and morphology of the synthesized silver particles were characterized using ultraviolet-visible spectroscopy, photopyroelectric technique, and transmission electron microscopy. It was found that for the both solvents, the effect of microwave irradiation was mainly on the particles distribution, rather than the size, which enabled to make stable and homogeneous silver nanofluids. The individual spherical nanostructure of self-assembled nanoparticles has been formed during microwave irradiation. Ethylene glycol solution, due to its special properties, such as high dielectric loss, high molecular weight, and high boiling point, can serve as a good solvent for microwave heating and is found to be a more suitable medium than the distilled water. A photopyroelectric technique was carried out to measure thermal diffusivity of the samples. The precision and accuracy of this technique was established by comparing the measured thermal diffusivity of the distilled water and ethylene glycol with values reported in the literature. The thermal diffusivity ratio of the silver nanofluids increased up to 1.15 and 1.25 for distilled water and ethylene glycol, respectively.

Keywords: Microwave heating; Nanofluids; Photopyroelectric; Silver nanoparticles; Thermal diffusivity.

Figure 1

Schematic diagram of PPE technique.

Figure 2

UV absorption spectrum during formation of Ag + PVP nanofluids and absorption spectrum of W3 after storage. (A) UV adsorption during the formation of Ag + PVP nanofluids (W₀, W_1, W_2, W₃. and W₄ at before and after 20, 40, 60, and 90 s MW irradiation times) was on the traces. (B) Absorption spectrum of W3 after storage for 2 and 6 months at room temperature.

Figure 3

UV absorption spectra during the formation of Ag/EG nanofluids at the various MW irradiation times.

Figure 4

TEM images and their size distributions of Ag NPs in DW at different MW irradiation time. 20 (A,B), 40 (C,D), 60 (E,F), and 90 s (G,H).

Figure 5

TEM images and their size distributions of Ag NPs in EG at different MW irradiation time. 20 (A,B), 40 (C,D), 60 (E,F), and 90 s (G,H).

Figure 6

TEM and FE-SEM images of the formation of dendritic and individual spherical nanostructures. (A) TEM and FE-SEM image of the formation of dendritic nanostructures of Ag NPs in DW solution. (B) The formation of TEM image of the individual spherical nanostructure self-assembled of Ag NPs colloids in EG solution.

Figure 7

The frequency behavior of the amplitude and phase of signal. (A) The frequency behavior of the amplitude of signal obtained from DW, (B) ln amplitude of PE signal versus the square root of the frequency, (C) ln (amplitude), and (D) phase of PE signal versus the square root of the frequency for one of the samples.

Figure 8

Variation of PE signal phase as function of square root of frequency for DW and EG solvents.

Figure 9

Thermal diffusivity ratio of Ag nanofluids with varying MW irradiation time for two solvents DW and EG.