Thermal and Molecular Insights into Betaine-Based Natural Deep Eutectic Solvents as Nanofluids Containing Amine-Functionalized Multiwalled Carbon Nanotubes

Currently, various strategies are being investigated and assessed to determine the most effective techniques for improving the heat transfer performance of heat transfer fluids, especially nanofluids. Natural deep eutectic solvents (NADESs) have arisen as sustainable options for eco-friendly processes and addressing the limitations of conventional fluids. This work presents a comprehensive synthesis of nanofluids formulated using NADESs as base fluids and amine-functionalized multiwalled carbon nanotubes (MWCNTs) as nanofillers. Two NADES systems, betaine:lactic acid (BF1, 1:2 mole ratio) and betaine:ethylene glycol (BF2, 1:4 mole ratio), were prepared and used to develop nanofluids with varying nanoparticle volume fractions (0.01–0.05). The thermal conductivity and decomposition behavior of the base fluids were evaluated experimentally. Enhanced heat transport properties were observed with the addition of nanoparticles, resulting in a 7–9% improvement in the thermal conductivity. Reverse nonequilibrium molecular dynamics (RNEMD) simulations confirmed these trends at the atomistic scale. The findings demonstrate the promise of NADES-based nanofluids as thermally efficient, environmentally friendly media for improved heat transfer applications.