Thermal Conductivity Enhancement of Cu- and Ag-Decorated MWCNT Hybrid Nanofluids Synthesized via Probe...

Hybrid Ag/MWCNT and Cu/MWCNT nanofluids were synthesized in ethylene glycol using a surfactant-free probe ultrasonication method and evaluated at ultralow solid concentration (0.001-0.01 wt%). TEM analysis indicated decoration of MWCNTs with Ag and Cu nanoparticles, while Raman spectroscopy indicated defect-mediated interactions and structural perturbation of the functionalized MWCNT framework, as suggested by increased I_D/I_G ratios. UV-Vis spectra showed Ag/MWCNT and Cu/MWCNT plasmonic bands at 380-420 and 300-360 nm, respectively, confirming dispersion in EG. At 0.001 wt%, periodic UV-Vis/zeta-potential tests over 4 weeks indicated acceptable stability, with preserved spectra and negative ζ values ≥30 mV. Thermal conductivity measurements (20°C-70°C) revealed clear enhancement with temperature and metal concentration, reaching ≈5.5% for Ag/MWCNT-EG and ≈8% for Cu/MWCNT-EG at 0.01 wt% and 70°C. The superior performance of Cu/MWCNT-EG is likely associated with stronger interfacial interactions between Cu and carboxylated MWCNTs, enabling more efficient phonon-electron heat transfer pathways. Compared with similar carbon-, metal-, and hybrid-based nanofluids commonly using ≥0.05-0.3 wt%, this work achieves measurable thermal improvement at 0.001-0.01 wt%, highlighting an effective, scalable, surfactant-free platform for designing stable, low-viscosity, high-performance heat transfer fluids for high heat flux heat exchangers, electronic cooling applications.