Remarkable Thermal Conductivity Enhancement in Carbon-Based Ionanofluids: Effect of Nanoparticle Morphology.

Bertrand Jóźwiak,Grzegorz Dzido,Marcin Libera,Marzena Dzida,Justyna Dziadosz,Anna Kolanowska,Sławomir Boncel,Rafał Jȩdrysiak,Edward Zorȩbski

doi:10.1021/acsami.0c09752

Abstract

Transfer of the excellent intrinsic properties of individual carbon nanoparticles into real-life applications of the corresponding heat transfer fluids remains challenging. This process requires identification and quantification of the nanoparticle–liquid interface. Here, for the first time, we have determined geometry and properties of this interface by applying transmission electron cryomicroscopy (cryo-TEM). We have systematically investigated how the particle morphology of carbon-based nanomaterials affected the thermal conductivity, specific isobaric heat capacity, thermal diffusivity, density, and viscosity of ionanofluids and/or bucky gels, using a wide range of fillers, especially single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs), both with extreme values of aspect ratio (length to diameter ratio) from 150 to 11 000. Accordingly, hybrid systems composed of various carbon nanomaterials and ionic liquid, namely 1-ethyl-3-methylimidazolium thiocyanate [EMIM][SCN], were prepared and characterized. Most of the analyzed nanodispersions exhibited long-term stability even without any surfactant. Our study revealed that the thermal conductivity could be remarkably improved to the maximum values of 43.9% and 67.8% for ionanofluid and bucky gel (at 1 wt % loadings of MWCNTs and SWCNTs), respectively, compared to the pristine ionic liquid. As a result, the model proposed by Murshed and co-workers has been improved for realistic description of the concentration-dependent thermal conductivity of such hybrid systems. The obtained results undoubtedly indicate the potential of ionanofluids and bucky gels for energy management.

Highlights

Increasing industrialization, as well as a better standard of living, has contributed to the increase in energy demand and miniaturization of heat transfer systems
Our study revealed that the thermal conductivity could be remarkably improved to the maximum values of 43.9% and 67.8% for ionanofluid and bucky gel, respectively, compared to the pristine ionic liquid
We have noticed that nanodispersions composed of [EMIM][SCN] + Tuball singlewalled carbon nanotubes (SWCNTs) at a weight percentage above 0.25 wt % formed bucky gels

Summary

Introduction

Increasing industrialization, as well as a better standard of living, has contributed to the increase in energy demand and miniaturization of heat transfer systems. The application of such functional materials is beneficial for enhanced conservation, transportation, or conversion of energy These energy processing areas remain one of the most important technical challenges in power generation, solar thermal systems, automobiles, precision manufacturing, microelectronics, and high-power laser optics.[1] One of the strategies to enhance the thermal conductivity of liquids is the addition of solid, thermally conductive nanoparticles. This solution was introduced by Maxwell more than a century ago.[2] In turn, the concept of ionanofluids (INFs) as dispersions of nanometer-sized solid materials (spheres, fibers, wires, tubes, sheets, etc.) in ionic liquids (ILs) was proposed in 2009 by Nieto de Castro et al.[3] INFs have rapidly gained importance in multiple fields, such as nanotechnology, chemical, and mechanical engineering. [EMIM][SCN] was denoted as an effective electrolyte for solar cells applications.[14]

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