Thermo-physical and stability properties of raw and functionalization of graphene nanoplatelets-based aqueous nanofluids

This research aimed to evaluate the thermal viscosity, stability, conductivity and density of coolants including PEG-functionalized graphene nanoplatelets (GNPs) and gum Arabic (GA)-treated GNPs as a base fluid at various temperatures and concentrations. The present study explores the impacts of GNPs functionalized with poly ethylene glycol (PEG) on the colloidal stability and thermophysical properties of water-based PEG-functionalized GNPs suspensions as a new generation of heat transfer fluids. To this end, PEG-functionalized GNPs as a covalent sample and GA-treated GNPs were synthesized and their colloidal stabilities were traced via UV–vis spectrometry. After functionalized, colloidal stability results indicate less sedimentation for covalent samples (less than 10%) that that of noncovalent one (almost 20%) after a 15-day period. In addition, all the thermophysical properties e.g. thermal conductivity, density and viscosity were measured experimentally. Further, it has shown that by loading PEG-functionalized GNPs in the water, the increasing rate of the density and viscosity is not significant, while water-based GA-treated GNPs nanofluids showed higher rates of increase. Interestingly, the water-based PEG-functionalized GNP nanofluids at very low concentration significantly increase the thermal conductivity in comparison with that of non-covalent nanofluid at the same concentration and temperature and defiantly water.     

Generalising the mean spherical approximation as a multiscale,nonlinear boundary condition at the solute–solvent interface

ABSTRACT

In this paper, we extend the familiar continuum electrostatic model to incorporate finite-size effects in the solvation layer, by perturbing the usual macroscopic interface condition. The perturbation is based on the mean spherical approximation (MSA), to derive a multiscale solvation-layer interface condition (SLIC/MSA). We show that SLIC/MSA reproduces MSA predictions for Born ions in a variety of polar solvents, including water as well as other protic and aprotic solvents. Importantly, the SLIC/MSA model predicts not only solvation free energies accurately but also solvation entropies, which standard continuum electrostatic models fail to predict. The SLIC/MSA model depends only on the normal electric field at the dielectric boundary, similar to our recent development of a SLIC model for charge-sign hydration asymmetry, and the reformulation of the MSA as an effective boundary condition enables its straightforward application to complex molecules such as proteins, whereas traditionally it is primarily a bulk theory. This work also opens the possibility for other electrolyte models to be incorporated into fast implicit-solvent models of biomolecular electrostatics.