Mechanisms behind the enhancement of thermal properties of graphene nanofluids

Abstract

While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π-π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties.

Multi-scale approach for modeling stability, aggregation, and network formation of nanoparticles suspended in aqueous solutions

“…Indeed, the addition of nanoparticles (NPs) to base fluids has demonstrated excellent promise by extending the technological frontiers in water treatment, 1,2 drug delivery, 3,4 nanomedicine, 5,6 energy storage, 7 and heat transfer. [8][9][10][11][12][13] Nevertheless, numerous experimental and theoretical challenges associated with coupling the macroscopic properties, like thermal conductivity and viscosity, with the nanoscale input parameters of nanoparticle suspensions (nano-suspensions), such as NP size, particle volume fraction, and particle surface chemistry, limit their rational design aimed at specific applications. 14 In this paper, we present a multi-scale model which is able to predict the dynamic behavior of NPs dispersed in aqueous solutions, thereby bringing us closer to delineating guidelines for modulating the stability and aggregation of nano-suspensions.…”

“…20 Finally, the generation of nanoparticle-chain morphologies in more dilute suspensions has demonstrated an enhancement of the overall thermophysical properties, thereby encouraging the use of nano-suspensions in the energy field. 12,21 Nevertheless, with respect to both improving the stability and promoting self-assembly, the role of nanoparticle interactions is salient in terms of altering the aggregation process, and thereby, the overall macroscopic properties of the assembled meso-structures and dispersions. 22,23 Experimental efforts on the targeted design of nano-suspensions have been largely lacking in the absence of a deeper understanding of the influence of NP surface chemistry on the stability of NP suspensions.…”

From Thermal to Electroactive Graphene Nanofluids

“…Graphene flakes with lateral sizes ∼150-450 nm and thicknesses from 1 to 10 layers were prepared from graphite (Sigma-Aldrich, purity >99% and size <20 µm) by a mechanical exfoliation method, as described in a previous work [11].…”

“…Graphene nanofluids are prepared by dispersing graphene (or RGO) nanosheets in an adequate base fluid. They can be stabilized in organic or aqueous solvents [6,8,10,11] in the form of pure, non-oxidized graphene [11] or rGO [8], but also in the form of hybrids [6,10]. All of these solvents present useful thermal or electrochemical properties, among others, as we summarize below.…”

Research Progress of the Liquid-Phase Exfoliation and Stable Dispersion Mechanism and Method of Graphene

“…Compared with traditional exfoliation and dispersion technologies (e.g., ultrasonic exfoliation and mechanical peeling), the above process extremely improved the exfoliated efficiency of graphene and satisfied the industrial requirement of large-scale preparation graphene. Although the dispersion of graphene is not prepared by using any surfactant, the large scale makes use of tetrahydrofuran, and NMP in the industry poses a certain safety hazard to human beings (Rodriguez-Laguna et al, 2018;Shabafrooz et al, 2018).…”