Ferrofluids (FFs) or magnetic nanofluids are incredible smart materials consisting of ultrafine magnetic nanoparticles suspended in a liquid carrier medium, which exhibit both fluidity and magnetic controllability. Studies involving the dynamics and physicochemical properties of these magnetic nanofluids are an interdisciplinary area of research attracting researchers from different fields of science and technology. Herein, a comprehensive Review on the different aspects of FF research is presented. First, the synthesis and stabilization of various types of FFs are discussed followed by their physicochemical features such as polydispersity, magnetic behavior, dipolar interactions, formation of chainlike aggregates, and long‐range ordering. The Review also details the rheological and thermal properties, dynamic instabilities, phase behavior, and particle assemblies in FFs to form complex multipolar geometries, photonic nanostructures, labyrinth structures, thin films, and droplets. Many important characterization techniques for probing FF properties are also briefly discussed, and the numerous innovative applications and future prospects of FFs are outlined.

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Stationary energy storage methods such as flow batteries are one of the best options to integrate with smart power grids. Though electrochemical energy storage using flow battery technologies has been successfully demonstrated since the 1970s, the introduction of ionic liquids into the field of energy storage introduces new dimensions in this field. This reliable energy storage technology can provide significantly more flexibility when incorporated with the synergic effects of ionic liquids. This mini-review enumerates the present trends in redox flow battery designs and the use of ionic liquids as electrolytes, membranes, redox couples, etc. explored in these designs. This review specifically intends to provide an overview of the research prospects of ionic liquids for redox flow batteries (RFB).

A comprehensive study on the structure, nature of interaction, and properties of six ionic pairs of 1-butylpyridinium and 1-butyl-4-methylpyridinium cations in combination with tetrafluoroborate (BF), chloride (Cl), and bromide (Br) anions have been carried out using density functional theory (DFT). The anion-cation interaction energy (ΔE), thermochemistry values, theoretical band gap, molecular orbital energy order, DFT-based chemical activity descriptors [chemical potential (μ), chemical hardness (η), and electrophilicity index (ω)], and distribution of density of states (DOS) of these ion pairs were investigated. The ascendancy of the -CH substituent at the fourth position of the 1-butylpyridinium cation ring on the values of ΔE, theoretical band gap and chemical activity descriptors was evaluated. The ΔE values were negative for all six ion pairs and were highest for Cl containing ion pairs. The theoretical band gap value after -CH substitution increased from 3.78 to 3.96 eV (for Cl) and from 2.74 to 2.88 eV (for Br) and decreased from 4.9 to 4.89 eV (for BF). Ion pairs of BF were more susceptible to charge transfer processes as inferred from their significantly high η values and comparatively small difference in ω value after -CH substitution. The change in η and μ values due to the -CH substituent is negligibly small in all cases except for the ion pairs of Cl. Critical-point (CP) analyses were carried out to investigate the AIM topological parameters at the interionic bond critical points (BCPs). The RDG isosurface analysis indicated that the anion-cation interaction was dominated by strong H···X and C···X interactions in ion pairs of Cl and Br whereas a weak van der Waal's effect dominated in ion pairs of BF. The molecular electrostatic potential (MESP)-based parameter ΔΔV measuring the anion-cation interaction strength showed a good linear correlation with ΔE for all 1-butylpyridinium ion pairs (R = 0.9918). The ionic crystal density values calculated by using DFT-based MESP showed only slight variations from experimentally reported values.

An iron oxide based-electroactive IoNanofluid with a high dielectric constant, high stability and low viscosity was synthesized from ferrous sulphate heptahydrate via a facile microwave assisted one-step route in 1-butyl-4-methylpyridinium chloride.