Effect of water adsorption at nanoparticle–oil interface on charge transport in high humidity transformer oil-based nanofluid

Transformer oil-based nanofluids (NFs) with TiO2 semiconductive nanoparticles (SNFs) exhibit substantially higher AC breakdown voltage than that of pure transformer oils at variable relative humidity from 20% to 80%. Charge accumulation and decay characteristics of pure oils and SNFs were measured by the pulse electroacoustic technique (PEA). It reveals that SNFs have more uniform internal electric fields and higher charge decay rate compared to pure oils under high relative humidity. It is confirmed by the test results of electrophoresis and thermally stimulated current (TSC) that the nanoparticles adsorb water molecules at the nanoparticle–oil interface, giving rise to the higher shallow trap density and resulting in better charge transport in SNFs.

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► Water molecules could be bound to the nanoparticle–oil interface.
► Water adsorption enhances the lateral conductive path along the interface.
► The change at interfaces accelerates charge hopping transport process in SNFs.
► Rapid transfer of charge carriers mitigates the accumulation of space charge.