Atomically precise understanding of nanofluids: nanodiamonds and carbon nanotubes in ionic liquids

Modification of insulating oils and oil-based titanium dioxide nanofluids for transformers: a review

In the last decade, oil-based titanium dioxide nanofluids (TiO2 NFs) have gained immense interest due to their unique insulating properties and excellent thermal performance, which endow them with the potential for application in the field of modified insulating oils. A timely comparison, analysis and summary of recent advances in the preparation, characterization, and properties of different oil-based TiO2 NFs for oil-immersed power transformers will contribute to provide a useful reference for the subsequent development of such materials. Preparation methods are reviewed along with their merits and demerits. Characterization techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy (OM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy, thermally stimulated current (TSC), pulse electroacoustic technique (PEA), finite element analysis (FEA), fluorescence spectroscopy, Raman spectroscopy and zeta potential analysis are all applied to determine the crystal structure, particle size, surface function, surface charge and stability. Stabilization mechanisms are also discussed in detail. Some critical properties of oil-based TiO2 NFs under the application of different influencing factors such as base oils, crystal structure, size of nanoparticles, surface modifiers, mixing percentage, and aging environment are highlighted. Finally, the existing challenges and perspectives are presented for future research.

Mechanisms behind the enhancement of thermal properties of graphene nanofluids

While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π-π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties.

Ten Things You Might Not Know about Iron Oxide Nanoparticles

Since ultrasmall superparamagnetic iron oxides (USPIOs) are not associated with a risk of nephrogenic sclerosis, they can serve as a safer contrast agents compared with gadolinium chelates for MR angiography, tissue perfusion studies, and atherosclerotic plaque and tumor imaging; USPIOs are especially beneficial for patients with renal insufficiency or patients with uncertain creatinine laboratory values.

Amid mounting concerns about nephrogenic sclerosis and gadolinium deposition in the brain, physicians and patients alike are starting to question the use of gadolinium chelates for clinical magnetic resonance (MR) imaging. The search for safer alternatives is currently underway. In North America, the iron supplement ferumoxytol has gained considerable interest as an MR contrast agent. In Europe, ferumoxtran-10 is entering phase III clinical trials. As these agents are starting to be used by a new generation of radiologists, important clinical questions have re-emerged, including those that have been answered in the past. This article offers 10 important insights for the use of iron oxide nanoparticles in clinical MR imaging.

Solubility origin at the nanoscale: enthalpic and entropic contributions in polar and nonpolar environments

Nanostructures are known to be poorly soluble, irrespective of their elemental composition, shape, electronic structure, dipole moment, hydrophobicity/hydrophilicity and the employed solvent. The methods of colloid chemistry allow for preparing suspensions - metastable systems, the stabilities of which differ greatly from one another - but not real solutions. A systematic investigation of the solubility origin at the nanoscale is hereby reported in terms of its fundamental constituents: enthalpy and entropy. Slightly different one-dimensional solutes - narrow carbon nanotubes (CNTs) of different lengths - were considered in hydrophilic (water) and hydrophobic (benzene) environments. We decompose the process of solvation into the solid → gas transition (sublimation) and the gas → liquid transition (condensation). Sublimation is a thermodynamically unfavorable process under room conditions, while the condensation transition depends on the solvent-solute interactions (enthalpic contribution). Unlike solvation of small molecules, solvation of the nanostructures results in a significant alteration of entropy. This alteration is proportional to the linear dimensions of the nanostructure. If the solvent exhibits peculiar solvent-solvent interactions (such as hydrogen bonding in water), solvation is entropically forbidden, irrespective of the solute nature and its nanoscale dimensions. In the case of the hydrophobic solvent (benzene), the condensation transition can be both enthalpically and entropically favorable. The free energy of solvation is in direct proportion to the CNT length. While highlighting principal difficulties in solvating nanostructures, this paper discusses an optimal choice of solvents for solutes exhibiting hydrophobic and hydrophilic interactions with their environments. Our results allow us to predict the solvation of an arbitrary nanostructure using its small, about 2 nm, atomistic model.