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The experiments have shown qualitative changes in electron paramagnetic resonance (EPR) spectra with decreasing average size of diamond particles from 100 μm to 18 nm. The characteristic hyperfine splitting in the EPR spectrum due to the interaction of an unpaired electron of a neutral impurity (nitrogen atom) in the diamond lattice with its nuclei disappears, and the resulting EPR spectrum is a superposition of two singlet Lorentzian lines. The reason for the observed effect is the indirect exchange interaction of electrons localized on bulk impurity centers through electrons localized on surface dangling bonds. Such an interaction of electrons localized on bulk centers becomes possible due to the resonant energy transfer between them. The transfer is result of the exchange interaction with electrons of surface centers. It is shown, that the energy of the indirect exchange interaction depends on the size of the diamond particle; therefore, the effect can be observed only in the case when particle size is smaller than a critical value R cr. The calculated value of the R cr based on the suggested model fitted well with experimental data. [ABSTRACT FROM AUTHOR]

We report on preparation, NMR and MRI study of suspensions of detonation nanodiamonds (DNDs) with manganese ions directly grafted to their surfaces, which are considered as novel contrast agents for MRI. We measured proton relaxation times, relaxivities and MRI images in aqueous and saline suspensions of manganese-grafted nanodiamonds, and those covered by polyvinylpyrrolidone, with different manganese concentrations. A comparison of the above parameters in Mn-grafted DNDs with those in the recently studied Gd-grafted DNDs and Dotarem, a contrast agent usually used in clinical practice, leads to a conclusion that Mn-grafted DNDs may serve as contrast agents for MRI. [Display omitted] • Nanodiamond suspensions • Manganese grafted nanodiamonds • Relaxivities • NMR • MRI [ABSTRACT FROM AUTHOR]

Suspensions of hydrogenated detonation nanodiamond (DND) particles in mineral oil are electrorheological fluids: their viscosity and yield stress increase under an electric field. The effect of the initial DND particles size obtained during the explosion on the properties of low-filled (up to 4 wt%) electrorheological fluids was considered. The small-angle X-ray scattering method revealed the differences in the structural organization of DNDs with sizes of 3 and 5 nm in a mineral oil, which affects the sedimentation stability of suspensions and their electrorheological behavior. The sedimentation ratio and the values of the yield stress are lower for 3 nm particles suspensions in the whole studied electric field strength (0–6 kV/mm). The method of impedance dielectric spectroscopy showed the differences in the electrophysical characteristics of suspensions filled with particles of 3 and 5 nm. The activation energies of polarization processes were estimated from the temperature dependences of the dielectric loss modulus. The study shows the key role of filler size for creating high performance electrosensitive materials and hypothesizes the reasons for different properties of electrorheological fluids filled by 3 and 5 nm DND particles. [Display omitted] • Suspensions of detonation nanodiamonds in mineral oil are electrorheological fluids. • The size of detonation nanodiamonds plays an important role in the rheological behavior of suspensions. • The branching of fractal structure in suspension depends on detonation nanodiamond particles size. [ABSTRACT FROM AUTHOR]

We used X-ray diffraction, small-angle X-ray scattering, and scanning electron microscopy (SEM) to study the diamond graphite phase transition in detonation nanodiamond (ND) intercalated with Cu, Ni, Co and Fe for the first time. The study has been made before and after annealing in hydrogen and argon. The SEM data obtained support the idea of the hierarchic structure of ND with a size of primary cluster of about 5 nm. There are several levels of aggregation of primary clusters. We have shown that all the samples of ND are surface fractals. It means the structure can be characterized by three parameters: coherent scattering region (CSR), the size of scatterer A and fractal dimensionality D.The transition degree was identified by X-ray diffractometry from the peaks of bulk nanographite. Scanning electron microscopy was used to determine the sizes of metallic and carbon aggregates. We have found from the CRS, A and D data that the intercalation does not practically change the diamond core at annealing in hydrogen and its size is similar to that reported earlier. However the changes of the scatterer size and fractal dimensionality depend on type of intercalated metals in hydrogen annealing. [Copyright &y& Elsevier]

Nanodiamond (ND) is one of the most attractive allotropic modification of carbon due to their unique physical and chemical properties. In the present review the current state of science and technology in the field of NDs is analyzed. ND can be used in various application and in different form e.g. as a dispersion phase in suspension, as a filler in composites, etc., so the sedimentation stability of ND in different media are under scrutiny. Thus, theoretical aspects of ND suspension coagulation mechanisms and the methods avoiding it were considered. The dependence of rheological behavior on particles modification was discussed as well. Various methods for the preparation and modification of NDs to obtain particles of various sizes on a nanometer scale with different physicochemical properties were reviewed. The area of practical application for NDs was considered on the example of polymer composites. The various manufacturing methods, mechanical properties and medical aspects for thermosetting, thermoplastic and elastomer ND composites were summarized., (Copyright © 2019. Published by Elsevier B.V.)

Ultrathin graphene films find their use as advantageous support for nano- and biomaterials investigations. Thin film causes a very slight deterioration to measured signals, thus providing more details of the object's structure at nanoscale. The ultimate thinness of graphene works in the best way for this purpose. However, obtaining suspended thin film of a large-area, which is convenient for applications, is often a relatively complicated and time-consuming task. Here we present a one-step 1-min technique for synthesis of an extremely thin (about 1-2 nm) continuous film suspended over cells of a conventional copper grid (50-400 μm mesh). This technique enables us to acquire a large-area film which is water-resistant, stable in organic solvents and can act as a support when studying nanoparticles or biomaterials. Moreover, the very mechanism of the film formation can be interesting from the point of view of other applications of ultrathin graphene oxide papers., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Intrinsic paramagnetic defects in ∼5 nm sized nanodiamonds, produced by various dynamic synthesis (DySND) techniques (detonation, shock-wave, pulsed laser ablation of solid carbon containing targets), have been studied by multi-frequency electron paramagnetic resonance (EPR). X-band (9-10 GHz) EPR spectra of DySND, in addition to the main intensive singlet Lorentzian-like EPR signal, reveal a low intensity doublet pattern within the half-field (HF) region (g ∼ 4). On transferring spectra to the Q-band (34 GHz) the shape of the HF pattern changes and splitting between doublet components is reduced from 10.4 to 2.6 mT. The HF patterns observed are attributed to the 'forbidden' ΔM(S) = 2 transitions between the Zeeman levels of some spin-triplet (S = 1) centers. The model of two triplet centers with g ∼ 2.003 and zero-field splitting parameters D(1) = 0.095 cm(-1) (TR1) and D(2) = 0.030 cm(-1) (TR2) satisfactorily describes experimental results at both microwave frequencies. The spin-triplet-type defects are observed in a wide variety of DySND samples irrespective of industrial supplier, cooling and carbon soot refinement methods, initial purity, disintegration, or subsequent targeted chemical modification. This indicates that the intrinsic defects with S = 1 in DySND systems are of universal origin.

We have developed a colloidal crystal templating method for preparation of diamond films with 2D and 3D ordered porous structures. The technological process involved breaks down into (a) impregnation into the pores of silica colloidal crystal (opal) films of detonation nanodiamond (DND) particles from their hydrosol; (b) microwave plasma-enhanced chemical vapor deposition (MWPECVD) regrowth with diamond of pores with high DND filling; (c) Ar(+) ion dry etching of fragments of shells of coalesced diamond crystallites which form in the course of MWPECVD on the surface of the SiO(2) beads making up the outer surface of a film and (d) wet etching of the SiO(2) template in aqueous HF solution. The final samples are either connected to the substrate or free-standing films of various thicknesses having 2D or 3D ordered porous structures. The morphology of the diamond films fabricated by this method replicates the pore network of the opal template. Raman measurements confirm the diamond structure of the synthesized ordered porous material.