Graphene IoNanofluids, Thermal and Structural Characterization.

C Hermida-Merino,A.B Pereiro,C Gracia-Fernández,Luis Lugo,J.M.M Araújo,Javier P Vallejo,M.M Piñeiro

doi:10.3390/nano9111549

Abstract

Graphene is considered a promising substance in applications related to the capture and reduction of the environmental impact of fluorinated gases. However, further research is still required to explore all related possibilities. In this work, the potential use in this context of nanofluids (NFs), obtained by dispersing graphene nanosheets in fluorinated ionic liquids (FILs) is investigated. As a starting step, a thermal and structural characterization for this type of IoNanofluids (IoNFs) is presented. The highly nanostructured nature of FILs has been recently demonstrated. The presence of fluorinated moieties is responsible for enhancing the accommodation of solutes such as small gases. The strong tendency to self-assemble forming continuous and supramolecular structures, and the versatility to rearrange in several conformational features allows the stabilization of nano colloidal systems. It is essential to perform a comprehensive study of their structural features to understand the behavior of this type of heterogeneous systems. Therefore, we present screening on the phase and structural behavior of these novel IoNFs to discover and develop optimized systems where FILs turn out to be advantageous. Thermogravimetric analysis (TGA) was employed to evaluate IoNFs mass losses with temperature, and their solid–fluid phase transitions were located using a differential scanning calorimeter (DSC). Their rheological properties were also determined through oscillatory experiments, obtaining the viscous and loss moduli. In addition, the structural percolation transition was also identified.

Highlights

During the last decades, intensive research has been performed concerning ionic liquids (ILs) because they have been identified as environmentally friendly solvents in a wide range of applications [1], including chemical synthesis, purification processes, and catalysis [2,3,4]
In the weight loss step, the sample remained constant until decomposition occurred above 600 K, with a weight loss below 6% and a degradation temperature Tonset = 686 K
If we focus on the cooling ramp, it is clear that the fluorinated ionic liquids (FILs), after the onset point at 251 K, presented six exothermic crystallization peaks, the first of them appearing at 250 K

Summary

Introduction

Intensive research has been performed concerning ionic liquids (ILs) because they have been identified as environmentally friendly solvents in a wide range of applications [1], including chemical synthesis, purification processes, and catalysis [2,3,4] Considering their structure, and comparing them with the traditional organic solvents, IL molecular structure is constituted by a large size and asymmetric organic cation and an anion of either inorganic or organic nature. A survey of the literature reveals that this application of graphene in NF formulation is finding application, for instance, in heat transfer processes and energy production optimization [9,10,11], but as discussed in the present paper, there are several other potential applications The target of this combination is to improve their heat transfer properties and tune their viscoelastic behavior. The use of ionic liquids (ILs) as a base fluid is a successful route to further improve the stability and viscosity of standard NFs

Methods

Results

Conclusion