The role of interfacial zone in dielectric properties of transformer oil-based nanofluids

Transformer oil-based nanofluids have unexpected and distinctive dielectric properties that are different from properties of constituting components. This is believed to be attributed to the effect of interfacial zone between oil and nanoparticles. Accordingly, this paper aims to investigate the role through which the interfacial zone affects the dielectric properties of transformer oil-based nanofluids. Oil-based nanofluids are prepared with two different types of nanoparticles having different surface charging polarity. These types are alumina (Al
₂
O
₃
) nanoparticles with cationic surface and titania (TiO
₂
) nanoparticles with anionic surface. For each type of nanoparticles, two groups are prepared with and without a surface modifier, which is called surfactant. Each group consists of four samples having nanoparticles weight fractions of 0.01, 0.04, 0.07 and 0.1 g/L. Surfactant is chosen with charge opposite to that of nanoparticle surface charge to be adsorbed on the nanoparticle surface. For each nanofluid sample, surfactant is distributed through the oil using magnetic stirrer, and then, nanoparticles are mixed and homogenized using magnetic stirrer and ultrasonic processing. After preparation, dielectric properties including breakdown strength and dielectric constant are measured. Based on the obtained results, the role of interfacial zone could be clarified in conjunction to that developed in solid nanodielectrics.