Heat transfer fluids: amino acid anion ionic liquid based IoNanofluids with remarkable thermal conductivity and low viscosity†

Present study aims to develop ionic liquid based nanofluids (IoNanofluids) exhibiting low viscosity, high thermal conductivity, thermal stability, high specific heat capacity and colloidal stability for potential heat transfer fluids applications. Four amino acid anion ionic liquids (AAIL) such as 1-butyl,3-metylimidazolium glycinate, 1-butyl,3-metylimidazolium arginate, 1-ethyl,3-metylimidazolium glycinate, 1-ethyl,3-metylimidazolium arginate were synthesized. The IoNanofluids (INF) were developed by adding 0.05 wt% of MWCNT to the AAILs. The effect of MWCNT concentration and surfactant was investigated by developing INFs consisting of 1-butyl, 3-methylimidazolium tetrafluoroborate ([bmim]⁺[BF₄]⁻) and MWCNT in the range of 0.025–0.1 wt%. The AAILs showed significantly less viscosity (18–8 mPa s at 298 K), higher thermal conductivity and specific heat capacity compared to several conventional ionic liquids. The four AAIL INFs showed 21–40% enhancement in thermal conductivity; very less viscosity (20 mPa s vs. 110 mPa s at 300 K), and remarkably higher specific heat capacity (10 J g⁻¹ °C vs. 1 J g⁻¹ °C) compared to [bmim]⁺[BF₄]⁻ INF. The AAIL INFs showed fine and homogeneous dispersion of MWCNT and substantially higher colloidal stability (30 days) compared to [bmim]⁺[BF₄]⁻ (7 days) and [bmim]⁺[BF₄]⁻ + MWCNT + CTAB (14 days). The AAIL INFs of present study showed enhanced heat transfer properties than several literature reported INFs made from conventional ionic liquids. Therefore, based on the overall properties, the AAIL INFs developed in present study could be suitable for applications such as heat exchangers, thermal energy storage systems, cooling of microprocessor systems broadly in the temperature range of 0–200 °C.