Properties Of Nanographene Research Articles

Characteristic features of nanofluids application in power engineering

The problem of increasing the intensity of heat transfer is an urgent and important task. Methods of increasing the heat transfer coefficient in cooling systems of power equipment are of particular interest. Over the past two decades, a promising area of research in this area is the study of heat transfer using nanofluids. To date, domestic and foreign authors have performed a large amount of research. The scientific search is conducted in several directions: the choice of a heat-conducting material and a base fluid; the study of the influence of nanoparticle concentration and size on the intensity of heat exchange. To increase the thermal conductivity of the heat transfer agents, it is proposed to use both pure metals (Au, Cu, Fe), their oxides (CuO, Al2O3, TiO2), and carbon nanomaterials. The base fluid is mainly distilled water, mineral oil, or ethylene glycol. Almost all authors note an increase in the thermal conductivity of the nanofluid up to 40% on average compared to the base fluid. The concentration of nanoparticles in experiments does not exceed 4%. However, the studies performed often give results that significantly contradict the theory of convective heat transfer. Thus, many authors note that the heat transfer coefficient in the laminar mode of the nanofluid is greater than that of the base fluid, and the reverse is observed in the turbulent mode. A convincing explanation for this phenomenon has not yet been found. There is also no reliable data on the portable properties of materials used for the manufacture of nanofluid, in particular, there is little data on the properties of nanographene. In the article, the authors review the studies of heat transfer using nanofluid, consider the possibility of using nanotubes and multigraphen to increase the thermal conductivity of the heat transfer agent. The authors also analyze existing models of heat transfer in nanofluids.

Properties of nanographene in polymer nanocomposites through all-atom simulations: Shape fluctuations and rippling

Conformational transitions of graphene can have a strong impact on the overall properties of graphene-based nanocomposites. Here we present a detailed analysis of the behavior of nanographene sheets embedded in polymer matrices, through all-atom Molecular Dynamics simulations. Thermal fluctuations of nanographene, in terms of rippling, are examined both statically and dynamically. Several different factors are investigated: a) Different polymers matrices; b) Edge functionalization of graphene; c) Size of the nanographene flake and d) Temperature effect.Polymer-graphene interactions induce fluctuations in the overall shape of the sheet. Examining the morphological transitions of the sheets in the atomic level, the role of functional groups is found to be critical and prevalent of other factors in the rippling of nanographene. More and higher ripples are formed at the edges of the functionalized sheets. Functionalization of the nanographene sheet reduces the mean number of the formed crests and troughs in the central part of the flake, compared to pristine graphene, whereas a clear increase is observed at the edges of the carboxylated sheets. Edge functional groups suppress the amplitude, as well as the kinetics of rippling compared to pristine nanographene, providing an effective way to control the conformational changes of nanographene.

Highly Regioselective Domino Benzannulation Reaction of Buta‐1,3‐diynes To Construct Irregular Nanographenes

AbstractThe properties of nanographenes can be tuned by changing their shapes, therefore the development of new methods suitable for the synthesis of various nanographenes is highly desirable. Described herein is an intramolecular InCl3/AgNTf2‐catalyzed regioselective domino benzannulation reaction of buta‐1,3‐diynes to build irregular nanographenes. Different nanographene compounds were easily obtained in moderate to high yields through careful design of the precursor compounds. This new domino reaction was successfully applied to a fourfold alkyne benzannulation of dimethoxy‐1,1′‐binaphthalene derivatives to arrive at novel chiral butterfly ligand precursors. The regioselectivity of the benzannulation reaction was unambiguously confirmed by X‐ray crystallography. Moreover, this new method enables us to synthesize different nanographene isomers and study their optical properties as a function of shape.

Highly Regioselective Domino Benzannulation Reaction of Buta-1,3-diynes To Construct Irregular Nanographenes.

The properties of nanographenes can be tuned by changing their shapes, therefore the development of new methods suitable for the synthesis of various nanographenes is highly desirable. Described herein is an intramolecular InCl3 /AgNTf2 -catalyzed regioselective domino benzannulation reaction of buta-1,3-diynes to build irregular nanographenes. Different nanographene compounds were easily obtained in moderate to high yields through careful design of the precursor compounds. This new domino reaction was successfully applied to a fourfold alkyne benzannulation of dimethoxy-1,1'-binaphthalene derivatives to arrive at novel chiral butterfly ligand precursors. The regioselectivity of the benzannulation reaction was unambiguously confirmed by X-ray crystallography. Moreover, this new method enables us to synthesize different nanographene isomers and study their optical properties as a function of shape.

A short review of nanographenes: structures, properties and applications

ABSTRACTGraphene has attracted great interest in the science and technology since it was exfoliated mechanically from the graphite in 2004. Although graphene has various potential applications, its practical applications are constrained enormously by its serious drawbacks, such as zero band gap, tendency of aggregation between layers and hydrophobicity, which mainly caused by the infinite planar hexagonal structure of graphene. Considering that the structural defects in the honeycomb lattice and the edges of graphene break the infinite structure and thus change the properties, which may improve the application efficiency, nanographene (NG) is proposed and attracts extensive attention. In this work, we review the structures of multifarious well-defined NGs synthesised in recent experiments. The effects of the shape, size, edges and substituents of NGs to the properties are discussed in detail and the regulation for various properties of NG is analysed. For the well-defined NGs, including planar and non-planar ones, the challenges and perspectives of their potential applications in nonlinear optical material, gas molecular detector and gas separation material, hydrogen storage material, and hole-transporting material in perovskite solar cells are envisioned.

Vibrational properties of nanographene

The eigenmodes and the vibrational density of states of the ground state configuration of graphene clusters are calculated using atomistic simulations. The modified Brenner potential is used to describe the carbon-carbon interaction and carbon-hydrogen interaction in case of H-passivated edges. For a given configuration of the C-atoms the eigenvectors and eigenfrequencies of the normal modes are obtained after diagonalisation of the dynamical matrix whose elements are the second derivative of the potential energy. The compressional and shear properties are obtained from the divergence and rotation of the velocity field. For symmetric and defective clusters with pentagon arrangement on the edge, the highest frequency modes are shear modes. The specific heat of the clusters is also calculated within the harmonic approximation and the convergence to the result for bulk graphene is investigated.

Growth, Characterization, and Properties of Nanographene

A systematic study on nanographene grown directly on silicon dioxide substrates is reported. The growth is carried out in a remote plasma-enhanced chemical vapor deposition system at a low temperature of around 550 °C with methane gas as the carbon source. Atomic force microscopy is used to characterize the nanographene morphology, and Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning tunneling microscopy are exploited to identify the in-plane sp(2) bonding structures of nanographene samples. Electrical transport properties are measured at various temperatures down to 4 K. Tunneling effects, minimal conductance at the charge-neutral point, sheet resistances, and Dirac point position at different channel lengths are investigated. In addition, nanographene film possesses high transmittance properties, as indicated by transmittance spectra. Nanographene devices are fabricated from rippled structures, and show great promise for strain-gauge sensor applications.