Investigation on Dielectric Insulation and Improvement of Thermal Properties of TiO₂-based Nanofluids with Carbon Quantum Dot Surface Functionalization

Advanced dielectric fluids with improved thermal and electrical insulation are needed for the operation of stationary power systems, hybrid electric vehicle technology and pulse power generation systems. The present commercial dielectric fluids do not meet the stringent demands required for these technologies to optimise energy efficiency and system reliability. In this research, Carbon Quantum Dots (CQDs) were used to modify the surface of titanium nanomaterials to enhance both their dielectric and thermal properties. To optimise the dielectric properties, we selectively coated CQDs onto the titanium nanomaterials with tailored dielectric constants to determine their dielectric constant, loss factor, capacitance, volume resistivity, flash point, fire point, and viscosity. Three different concentration ratios of functionalized nanomaterials (mass fractions of 0.01%, 0.05%, and 0.1%) in mineral oil to were used to prepare three different types of nanofluids for evaluation. The results show there was an increase in breakdown strength (up to 15-20kV), dielectric constant (10-15%) and volume resistivity (from 1×1013 Ω·cm to 4.5×1013 Ω·cm). The loss factor reduced to 0.001 from 0.007. Additionally, the evaluation showed that the functionalized nanomaterials significantly increased the flash and fire points of the nanofluids by 10-19℃. Surface functionalization using CQDs promotes uniform nanoparticle dispersion and stabilizes interfacial charge polarization and relaxation processes. These effects collectively contribute to an increase in relative permittivity, a lower loss factor, and sustained capacitance behavior in the dielectric system.