Investigation on Dielectric Insulation and Improvement of Thermal Properties of TiO₂-based Nanofluids with Carbon Quantum Dot Surface Functionalization
J. Environ. Nanotechnol., Volume 14, No 4 (December 2025) pp. 319-328
Abstract
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.
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Reference
Abdi, S., Harid, N., Boubaker A., Haddad, M.and Boubakeur, A., Comprehensive assessment of transformer oil after thermal aging: modeling for simultaneous evaluation of electrical and chemical characteristics, Energies, 18(8), 1915 (2025).
https://doi.org/10.3390/en18081915
Bibi, S., Shakir, N., Sadiq, M., Sadiq, S., Ullah, I., Khan, Q., Bostan, B. and Ismail, M., Investigating the structural, dielectric, optical and photocatalytic properties of carbon dots and palladium, platinum decorated carbon dots, Mol. Struct., 138488(2024).
https://doi.org/10.1016/j.molstruc.2024.138488
Bojovschi, A., Quoc, T. V., Trung, H. N., Quang, D. T. and Le, T. C., Environmental effects on HV dielectric materials and related sensing technologies, Appl. Sci., 9(5), 856 (2019).
https://doi.org/10.3390/app9050856
Chandrasekar, S. and Montanari, G. C., Analysis of partial discharge characteristics of natural esters as dielectric fluid for electric power apparatus applications, IEEE Trans. Dielectr. Electr. Insul., 21(3), 1251–1259 (2014).
https://doi.org/10.1109/TDEI.2014.6832272
Danial, A. R., Walvekar, M., Khalid, M., Vaka,and Mubarak, N. M., Recent progress and challenges in transformer oil nanofluid development: a review on thermal and electrical properties, IEEE Access, 7, 151422–151438 (2019).
https://doi.org/10.1109/ACCESS.2019.2946633
Djurovic, D., Karaman, D., Vasic, D. and Pejanovic, D., Dielectric relaxation response of electrical insulating liquids under different natures of thermal stress, J. Mater. Res. Technol., 25, 1599–1611 (2023).
https://doi.org/10.1016/j.jmrt.2023.06.033
Dsouza, S. D., Buerkle, M., Brunet, P., Maddi, C., Padmanaban, D. B., Morelli, A., Payam, A. F., Maguire, P., Mariotti, D. and Svrcek, V., The importance of surface states in N‑doped carbon quantum dots, Carbon, 183, 1–11 (2021).
https://doi.org/10.1016/j.carbon.2021.06.088
Fofana, I., Bouaïcha, A., Farzaneh, M., Sabau, J., Bussières, D. and Robertson, E. B., Decay products in the liquid insulation of power transformers, IET Electr. Power Appl., 4(3), 177–184 (2010).
https://doi.org/10.1049/iet-epa.2009.0181
Girish, K. M., R. Lavanya, M. V., Hemantha, R. G. R., Rajath, B. N., Deepak, K. and Prashantha, S. C., Dielectric and conductivity studies of Tb-doped zinc orthotitanate nanomaterials for next-generation electronics and energy storage, Solid State Ionics, 432, 117048(2025).
https://doi.org/10.1016/j.ssi.2025.117048
Haque, S. M., Ardila-Rey, J. A., Umar, Y., Mas’ ud, A. A., Muhammad-Sukki, F., Jume, B. H. and Bani, N. A., Application and Suitability of Polymeric Materials as Insulators in Electrical Equipment, Energies, 14(10), 2758 (2021).
https://doi.org/10.3390/en14102758
Karataş, M. and Bicen, Y., Nanoparticles for next-generation transformer insulating fluids: A review, Renew. Sustain. Energy Rev., 167, 112645 (2022).
https://doi.org/10.1016/j.rser.2022.112645
Koch, M., Tenbohlen, S. and Djamali, M., Influence of thermal aging on dielectric properties of natural ester oil-impregnated paper, IEEE Trans. Dielectr. Electr. Insul., 17(3), 762–770 (2010).
https://doi.org/10.1109/TDEI.2010.5412009
Kong, J., Wei, Y., Zhou, F., Shi, L., Zhao, S., Wan, M. and Zhang, X., Carbon quantum dots: properties, preparation, and applications, Mol., 29(9), 2002 (2024).
https://doi.org/10.3390/molecules29092002
Küchler, A., High Voltage Engineering: Fundamentals – Technology – Applications, Springer Vieweg, 2018.
https://doi.org/10.1007/978-3-642-11993-4
León, A., Reuquen, P., Garín, C., Segura, R., Vargas, P., Zapata, P. and Orihuela, P. A., FTIR and Raman Characterization of TiO₂ Nanoparticles Coated with Polyethylene Glycol as Carrier for 2-Methoxyestradiol, Appl. Sci., 7(1), 49 (2017).
https://doi.org/10.3390/app7010049
Li, Y., Wang, K., Hou, W. and Wang, L., Carbon quantum dots for environmental catalysis: green synthesis, surface functionalization, and interface engineering, Chem. Commun., 61, 18784–18797 (2025).
https://doi.org/10.1039/D5CC04350F
Lundgaard, L. E., Hansen, W., Linhjell, D.and Painter, T. J., Aging of oil‑impregnated paper in power transformers: influence of moisture, oxygen and acidity on cellulose insulation, IEEE Trans. Power Delivery, 19(1), 121–131 (2004).
https://doi.org/10.1109/TPWRD.2003.820175
Lv, Y., Li, C., Sun, Q., Huang, M., Cheng, L. and Qi, B., Effect of Dispersion Method on Stability and Dielectric Strength of Transformer Oil‑Based TiO₂ Nanofluids, Nanoscale Res. Lett., 11, 515 (2016).
https://doi.org/10.1186/s11671-016-1738-5
Lyutikova, M., Korobeynikov, S. and Konovalov, A., Evaluation of the properties of mixtures of aromatic mineral oil and synthetic ester for high‑voltage equipment, IEEE Trans. Dielectr. Electr. Insul., 28(4), 1282–1290 (2021).
https://doi.org/10.1109/TDEI.2021.009636
Mansour, D. E. A., Shaalan, E. M., Ward, S. A.,El Dein, A. Z., Karaman, H. S. and Ahmed, H. M., Multiple nanoparticles for improvement of thermal and dielectric properties of oil nanofluids, IET Sci. Meas. Technol., 13(7), 968–974 (2019).
https://doi.org/10.1049/iet-smt.2018.5015
Palanisamy, K. V., Subramaniam, C. and Sakthivel, B., Evaluating the role of carbon quantum dots covered silica nanofillers on the partial discharge performance of transformer insulation, Turk. J. Electr. Eng. Comput. Sci., 30(4), 1492–1505 (2022).
https://doi.org/10.55730/1300-0632.3861
Palanisamy, K. V., Subramaniam, C. and Sakthivel, B., Investigations on novel carbon quantum dots covered nanofluid insulation for medium voltage applications, J. Electr. Eng. Technol., 15(1), 269–278 (2020).
https://doi.org/10.1007/s42835-019-00316-5
Parekh, K., Upadhyay, R., Rajňák, M., Dolník, B., Timko, M. and Kopčanský, P., Effects of static electric field and temperature on the dynamic dielectric responses of mixed oil‑based and bilayer‑stabilised magnetic fluids, Nanoscale, 17, 22927–22939 (2025).
https://doi.org/10.1039/D5NR02856F
Rafiq, M., Shafique, M., Ateeq, M., Zink, M.and Targitay, D., Natural esters as sustainable alternating dielectric liquids for transformer insulation system: analyzing the state of the art, Clean Technol. Environ. Policy, 25(4), 31 (2023).
https://doi.org/10.1007/s10098-023-02688-9
Saini, S. and Harid, N., Correlation between dielectric dissipation factor and resistivity in aged transformer oils, Energies, 16(1), 381 (2023).
https://doi.org/10.3390/en16010381
Salah, M. E., El‑Sharkawy, R., Ibrahim, M. A.and Abdel‑Galil, A. M., The role of the accumulated surface charge on nanoparticles in improving the breakdown strength of liquid and solid insulation, Energies, 15(13), 4860 (2022).
https://doi.org/10.3390/en15134860
Stone, G. C., Partial discharge diagnostics and electrical equipment insulation condition assessment, IEEE Trans. Diele. Electric. Insul., 12(5), 891-904 (2005).
https://doi.org/10.1109/tdei.2005.1522184
Suhaimi, S. N., Rahman, A. R. A., Md. Din, M. F., Hassan, M. Z., Ishak, M. T. and Jusoh, M. T. B., A Review on Oil-Based Nanofluid as Next-Generation Insulation for Transformer Application, J. Nanomater., 1–17 (2020),
https://doi.org/10.1155/2020/2061343
Szcześniak, D. and Przybylek, P., Oxidation stability of natural ester modified by means of fullerene nanoparticles, Energies, 14(2), 490 (2021).
https://doi.org/10.3390/en14020490
Viswanathan, P. K., Chandrasekar, S. and Sakthivel, B., Influence of CQD modified silica nano fillers on PD characteristics of transformer oil, IEEE 4th Int. Conf. Condition Assess. Tech. Electri. Syst., 1–5 (2019).
https://doi.org/10.1109/CATCON47128.2019.CN0051
Viswanathan, P. K., Chandrasekar, S. and Sakthivel, B., Influence of carbon quantum dots modified silica nanoparticles on insulation properties of mineral oil, Proc. Int. Conf. High Vol. Eng. Appli., 10(2019).
https://doi.org/10.1109/ICHVET.2019.8724259
Wang, B., Wu, H., Hou, W., Fang, Z., Liu, H., Huang, F., Li, S. and Zhang, H., Optimizing dielectric polarization for electromagnetic wave attenuation via an enhanced Maxwell–Wagner–Sillars effect in hollow carbon microspheres, J. Mater. Chem. A, 11(43), 23498–23510 (2023).
https://doi.org/10.1039/D3TA05647C
Wu, Y., Chen, R., Zhang, J. and Tang, C., The influence of doping with different surface‑modified SiO₂ nanoparticles on the dielectric properties of natural ester insulating oil, Renew. Energy, 228, 120671 (2024).
https://doi.org/10.1016/j.renene.2024.120671
Xia, G., Wu, G., Gao, B., Yin, H. and Yang, F., A New Method for Evaluating Moisture Content and Aging Degree of Transformer Oil‑Paper Insulation Based on Frequency Domain Spectroscopy, Energies, 10(8), 1195 (2017).
https://doi.org/10.3390/en10081195
Xue, Q., Timoshkin, I., Given, M. J., Wilson, M. P. and MacGregor, S. J., Mobility of charge carriers in dielectric liquids (mineral oil, synthetic and natural esters), High Vol., 6(6), 1040–1050 (2021).
https://doi.org/10.1049/hve2.12098
Yoon, H., Chen, G. and Hosier, I., Influence of thermal ageing on dielectric properties of natural ester oil‑impregnated paper, IEEE Trans. Dielectr. Electr. Insul., 30(3), 1337–1344 (2023).
https://doi.org/10.1109/TDEI.2023.3268039
Zhang, Z., Zuo, F., Cai, T., Gai, X., Wan, L., Lin, H., Wang, B. and Zhang, H., Modification of insulating oils and oil‑based titanium dioxide nanofluids for transformers: a review, Phys. Chem. Chem. Phys., 25, 22565–22582 (2023).
