Nuclear magnetic resonance-based study of ordered layering on the surface of alumina nanoparticles in water

Abstract

Layering of water molecules on the surface of alumina nanoparticles in an alumina/water nanofluid is studied using nuclear magnetic resonance ͑NMR͒. The data suggest that a thin ordered layer ͑ϳ1.4 nm͒ of water molecules surrounds each nanoparticle. This ordered layer increases the nanoparticle effective volumetric fraction; however, the nanofluid thermal conductivity appears to be unaffected by this layer, and in good agreement with Maxwell's effective medium theory. Furthermore, the NMR data suggest that the nanoparticles do not enhance, but rather stifle micromixing in the base fluid.

Mass transfer into/from nanofluid drops in a spray liquid‐liquid extraction column

“…[12][13][14][15][16][17] Mass transfer in nanofluids was extensively reviewed in a recent published article. 18 In the field of mass transfer in nanofluids, there are a few researches dealt with mass diffusion in nanofluids 10,12,[19][20][21][22][23][24][25] and more researches investigated the influence of nanoparticles on convective mass transfer. 13,15,16,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Nevertheless, most researches on convective mass transfer in nanofluids are related to the gas absorption processes [26][27][28][29][30][31][32][33][34][35] and there have been limited attempts to use nano...…”

Experimental investigation of benzoic acid diffusion coefficient in γ-Al2O3 nanofluids at different temperatures

“…Veilleux and Coulombe [24] measured the tracer mass diffusion of Rhodamine 6G in alumina nanofluids and observed that dye diffusion coefficient at an optimum nanoparticles concentration was ten times larger than that in the de-ionized water [24]. By using the pulsed field gradient nuclear magnetic resonance method, Turanov and Tolmachev [25] and Gerardi et al [26] measured the selfdiffusion coefficient of water in the aqueous suspension of SiO 2 and Al 2 O 3 nanoparticles, respectively. They showed that nanoparticles decreased mass diffusion coefficients by about 30 and 10 %, respectively [25,26].…”

Diffusiophoretic enhancement of mass transfer by nanofluids

“…Mass transfer studies in dye-diffusion by Krishnamurthy et al 1 and others [2,3] have demonstrated, through dramatic visual effects, that the presence of nanoparticles increases the effective diffusivity up to 14 folds. Yet, when carried out in other system configurations, there are some cases where no enhancement [16,17] and even a lowering of the diffusivity [18][19][20] are observed. Various possibilities have been advanced in an attempt to explain these intriguing observations: Brownian motion, micro-convection [1,2], interfacial complexation [16], dispersion model [21], etc., but none of them have been backed with conclusive evidence.…”

“…For a homogeneously mixed system, where the nanoparticles and the solute are uniformly dispersed, and the diffusivity is measured using Fluorescence Correlation Spectroscopy (FCS) [17] or Nuclear magnetic resonance (NMR) [18,19], no enhancement or a small lowering of the diffusivity of the solute has been reported. A significant * p.sunthar@iitb.ac.in enhancement is observed only in an inhomogeneous system (various configurations are shown in Figure 1) [1][2][3].…”