Vol.:(0123456789) International Journal of Thermophysics (2020) 41:168 https://doi.org/10.1007/s10765-020-02748-y 1 3 NANOPARTICLE-ENHANCED IONIC LIQUIDS Investigation of Iron Oxide‑Based Ionanofluids and Ionic Liquids by Ultrasonic Sound Velocity Method Aswathy Joseph 1  · Pankajakshan Radhakrishnan Nair 2  · Suresh Mathew 1,2 Received: 14 September 2020 / Accepted: 30 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Measurement of ultrasonic sound velocity in ionic liquids and ionanofluids can give important information about the liquid structure, nanoparticles interactions, effect of water, extent of intermolecular association and the kinetics of molecular processes. Here, the acoustic properties of certain pyridinium-based ionic liquids and their iron oxide-based ionanofluids have been studied using a nanofluid interferometer device. In the ionanofluids, the sound velocity was observed to decrease anisotropi- cally with increase in temperature. The magnetic dipolar interactions among the iron oxide nanoparticles, the nature of IL’s anion and cation as well as sound wave fre- quency also influenced the sound velocity in the ionanofluid. The effects of sound frequency, temperature and the percentage of water content on the sound velocity in certain pure ionic liquids have also been investigated here. Keywords 1-Butylpyridinium bromide · Ionanofluid · Ionic liquids · Nanofluid interferometer · Ultrasonic sound velocity 1 Introduction The use of ionic liquids (ILs) for manufacturing nanofluids (NFs) opens up new possibilities in the field of nanoparticles enhanced ionic liquids (NEILs) for advanced heat transfer applications [1–5]. Ionic liquids (IL) when used as carrier This article is part of the Special Issue on Nanoparticle-enhanced Ionic Liquids. * Suresh Mathew sureshmathewmgu@gmail.com Pankajakshan Radhakrishnan Nair ammrcmgu@gmail.com 1 School of Chemical Sciences (SCS), Mahatma Gandhi University, Kottayam, Kerala 686 560, India 2 Advanced Molecular Materials Research Centre (AMMRC), Mahatma Gandhi University, Kottayam, Kerala 686 560, India