Surface Modification of Nanoparticles Using Plasma Technology to Enhance the Insulation Properties and Stability of Nanofluids: A Review

The literature has shown that introducing nanoparticles into mineral oil is a potential approach to improving the liquid insulation's thermal and electrical performance. Nanoparticles' fundamental characteristics, such as conductivity and permittivity, can improve the relaxation time constant, thereby improving electrical performances, while the nanoparticles' Brownian motion may enhance the nanofluids' thermal conductivity. This manuscript includes a detailed analysis of the research on transformer oil-based nanofluids. Besides, a critical issue has been discovered: nanoparticle dispersion in transformer oil may result in sedimentation and agglomeration, affecting the stability and performance of nanofluids. The most typical approach for improving nanofluid dispersion and reducing sediment is to add a surfactant, but selecting the most effective surfactant remains challenging. An excess of surfactant added could cause an overabundance of change in nanofluid characteristics which is thermal conductivity and viscosity, which would be a concern in nanofluid applications. Therefore, many recent studies on plasma treatment for nanoparticle surface modification have been published. Plasma treatment, which is suitable for mass production, environmentally friendly, and easily operated, has emerged as the preferred method for modifying the surface of nanoparticles. This treatment may additionally eliminate the need for surfactants or other chemical dispersants to improve nanofluid stability and dispersion. There is currently a scarcity of research on plasma treatment in transformer oil-based nanofluids. Therefore, this manuscript reviews the non-conventional method of nanoparticle surface treatment known as atmospheric pressure plasma treatment, in an effort to improving the electrical, thermal, and the characteristics of transformer oil for power transformer applications, while also highlighting the culmination of the future direction of this non-conventional method of surface treatment for nanofluids.