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Crystals, Volume 8, Issue 4 (April 2018)

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Cover Story (view full-size image) One of the main concepts of structural design for low-dimensional magnetic systems is the [...] Read more.
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Open AccessArticle Shifting the Shear Paradigm in the Crystallographic Models of Displacive Transformations in Metals and Alloys
Crystals 2018, 8(4), 181; https://doi.org/10.3390/cryst8040181
Received: 2 March 2018 / Revised: 6 April 2018 / Accepted: 16 April 2018 / Published: 23 April 2018
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Abstract
Deformation twinning and martensitic transformations are characterized by the collective displacements of atoms, an orientation relationship, and specific morphologies. The current crystallographic models are based on the 150-year-old concept of shear. Simple shear is a deformation mode at constant volume, relevant for deformation
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Deformation twinning and martensitic transformations are characterized by the collective displacements of atoms, an orientation relationship, and specific morphologies. The current crystallographic models are based on the 150-year-old concept of shear. Simple shear is a deformation mode at constant volume, relevant for deformation twinning. For martensitic transformations, a generalized version called invariant plane strain is used; it is associated with one or two simple shears in the phenomenological theory of martensitic crystallography. As simple shears would involve unrealistic stresses, dislocation/disconnection-mediated versions of the usual models have been developed over the last decades. However, a fundamental question remains unsolved: how do the atoms move? The aim of this paper is to return to a crystallographic approach introduced a few years ago; the approach is based on a hard-sphere assumption and linear algebra. The atomic trajectories, lattice distortion, and shuffling (if required) are expressed as analytical functions of a unique angular parameter; the habit planes are calculated with the simple “untilted plane” criterion; non-Schmid behaviors associated with some twinning modes are also predicted. Examples of steel and magnesium alloys are taken from recent publications. The possibilities offered in mechanics and thermodynamics are briefly discussed. Full article
(This article belongs to the Special Issue Microstructures and Properties of Martensitic Materials)
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Open AccessArticle Ferroelectric Relaxor Quantum Crystals
Crystals 2018, 8(4), 180; https://doi.org/10.3390/cryst8040180
Received: 27 February 2018 / Revised: 17 April 2018 / Accepted: 18 April 2018 / Published: 21 April 2018
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Abstract
A discussion is given of ferroelectrics (FEs) that have their Curie temperatures Tc very near absolute zero. These have differences in their dynamics in comparison with higher-temperature systems, since domain wall motion occurs via quantum mechanical tunneling and not by thermally activated
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A discussion is given of ferroelectrics (FEs) that have their Curie temperatures Tc very near absolute zero. These have differences in their dynamics in comparison with higher-temperature systems, since domain wall motion occurs via quantum mechanical tunneling and not by thermally activated diffusion. Emphasis in the present paper is on FEs that have relaxor characteristics. In such systems, the temperature at which the isothermal electric susceptibility ε(T,f) peaks is a strong function of frequency, and it decreases with decreasing frequency. This is due to glassy viscosity and is symbolic of non-equilibrium dynamics, usually described by a Vogel-Fulcher equation. It permits an extra dimension with which to examine the transitions. The second half of this paper reviews domain wall instabilities and asks about their presence in QCP ferroelectrics, which has not yet been reported and may be unobservable due to the absence of thermal diffusion of walls near T = 0; in this respect, we note that diffusion does exist in ferroelectric relaxors, even at T = 0, by virtue of their glassy, viscous dynamics. Full article
(This article belongs to the Special Issue Quantum Crystals)
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Open AccessArticle Size Control of Cobalt-Doped ZnO Nanoparticles Obtained in Microwave Solvothermal Synthesis
Crystals 2018, 8(4), 179; https://doi.org/10.3390/cryst8040179
Received: 13 February 2018 / Revised: 9 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
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Abstract
This article presents the method of size control of cobalt-doped zinc oxide nanoparticles (Zn1−xCoxO NPs) obtained by means of the microwave solvothermal synthesis. Zinc acetate dihydrate and cobalt(II) acetate tetrahydrate dissolved in ethylene glycol were used as the precursor.
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This article presents the method of size control of cobalt-doped zinc oxide nanoparticles (Zn1−xCoxO NPs) obtained by means of the microwave solvothermal synthesis. Zinc acetate dihydrate and cobalt(II) acetate tetrahydrate dissolved in ethylene glycol were used as the precursor. It has been proved by the example of Zn0.9Co0.1O NPs (x = 10 mol %) that by controlling the water quantity in the precursor it is possible to precisely control the size of the obtained Zn1−xCoxO NPs. The following properties of the obtained Zn0.9Co0.1O NPs were tested: skeleton density (helium pycnometry), specific surface area (BET), dopant content (ICP-OES), morphology (SEM), phase purity (XRD), lattice parameter (Rietveld method), average crystallite size (FW1/5/4/5M method and Scherrer’s formula), crystallite size distribution (FW1/5/4/5M method), and average particle size (from TEM and SSA). An increase in the water content in the precursor between 1.5% and 5% resulted in the increase in Zn0.9Co0.1O NPs size between 28 nm and 53 nm. The X-ray diffraction revealed the presence of only one hexagonal phase of ZnO in all samples. Scanning electron microscope images indicated an impact of the increase in water content in the precursor on the change of size and shape of the obtained Zn0.9Co0.1O NPs. The developed method of NPs size control in the microwave solvothermal synthesis was used for the first time for controlling the size of Zn1−xCoxO NPs. Full article
(This article belongs to the Special Issue Microwave-Assisted Synthesis of Nanocrystals and Nanostructures)
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Open AccessArticle Characterization of Sub-Monolayer Contaminants at the Regrowth Interface in GaN Nanowires Grown by Selective-Area Molecular Beam Epitaxy
Crystals 2018, 8(4), 178; https://doi.org/10.3390/cryst8040178
Received: 22 March 2018 / Revised: 10 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
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Abstract
While GaN nanowires (NWs) offer an attractive architecture for a variety of nanoscale optical, electronic, and mechanical devices, defects such as crystal polarity inversion domains (IDs) can limit device performance. Moreover, the formation of such defects during NW growth is not fully understood.
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While GaN nanowires (NWs) offer an attractive architecture for a variety of nanoscale optical, electronic, and mechanical devices, defects such as crystal polarity inversion domains (IDs) can limit device performance. Moreover, the formation of such defects during NW growth is not fully understood. In this study, we use transmission electron microscopy (TEM) and atom probe tomography (APT) to investigate the effects of sub-monolayer contamination at the regrowth interface in GaN NWs grown by selective-area molecular beam epitaxy (MBE). TEM energy dispersive X-ray spectroscopy (EDS) and APT independently identified Al and O contamination localized at the regrowth interface in two of the three growth runs examined. The Al and O concentrations were each estimated to be on the order of 11% of an ideal c-plane monolayer in the most severely contaminated case. The amount of contamination correlated with the number of crystal polarity inversion domain defects (IDs) across the growth runs. A growth run in which the pre-regrowth HF vapor etch step was replaced by HCl immersion showed the smallest quantity of O and no measurable Al. In addition, many of the NWs examined from the HCl-treated growth run turned out to be free of IDs. These results suggest that sub-monolayer contamination introduced during processing contributes to defect formation in MBE-grown GaN NWs. Full article
(This article belongs to the Special Issue Growth and Structural Characterization of Self-Nucleated Nanowires)
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Open AccessArticle Analysis of Leaky Modes in Photonic Crystal Fibers Using the Surface Integral Equation Method
Crystals 2018, 8(4), 177; https://doi.org/10.3390/cryst8040177
Received: 1 March 2018 / Revised: 14 April 2018 / Accepted: 14 April 2018 / Published: 19 April 2018
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Abstract
A fully vectorial algorithm based on the surface integral equation method for the modelling of leaky modes in photonic crystal fibers (PCFs) by solely solving the complex propagation constants of characteristic equations is presented. It can be used for calculations of the complex
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A fully vectorial algorithm based on the surface integral equation method for the modelling of leaky modes in photonic crystal fibers (PCFs) by solely solving the complex propagation constants of characteristic equations is presented. It can be used for calculations of the complex effective index and confinement losses of photonic crystal fibers. As complex root examination is the key technique in the solution, the new algorithm which possesses this technique can be used to solve the leaky modes of photonic crystal fibers. The leaky modes of solid-core PCFs with a hexagonal lattice of circular air-holes are reported and discussed. The simulation results indicate how the confinement loss by the imaginary part of the effective index changes with air-hole size, the number of rings of air-holes, and wavelength. Confinement loss reductions can be realized by increasing the air-hole size and the number of air-holes. The results show that the confinement loss rises with wavelength, implying that the light leaks more easily for longer wavelengths; meanwhile, the losses are decreased significantly as the air-hole size d/Λ is increased. Full article
(This article belongs to the Special Issue Photonic Crystal Fiber)
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Open AccessArticle Solvent-Induced Unsymmetric Salamo-Like Trinuclear NiII Complexes: Syntheses, Crystal Structures, Fluorescent and Magnetic Properties
Crystals 2018, 8(4), 176; https://doi.org/10.3390/cryst8040176
Received: 26 March 2018 / Revised: 14 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
Solvent-induced trinuclear NiII complexes, [{Ni(L)(MeOH)}2(OAc)2Ni]·2MeOH (1), [{Ni(L)(EtOH)}2(OAc)2Ni]·2H2O (2), [{Ni(L)(n-PrOH)}2(OAc)2Ni]·2H2O (3) and [{Ni(L)(i-PrOH)}2(OAc)2Ni]
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Solvent-induced trinuclear NiII complexes, [{Ni(L)(MeOH)}2(OAc)2Ni]·2MeOH (1), [{Ni(L)(EtOH)}2(OAc)2Ni]·2H2O (2), [{Ni(L)(n-PrOH)}2(OAc)2Ni]·2H2O (3) and [{Ni(L)(i-PrOH)}2(OAc)2Ni] (4), have been prepared with an unsymmetric Salamo-like ligand H2L, and characterized via X-ray crystallography, FT-IR, UV-Vis and fluorescence spectra. In complexes 1, 2, 3 and 4, there are two ligand (L)2− moieties, two acetato ligands, two coordinated methanol, ethanol, n-propanol or i-propanol molecules, respectively, as well as other crystallizing solvent molecules. Two acetato ligands coordinated to the three NiII ions via usual Ni-O-C-O-Ni bridges, and four µ-phenoxo oxygen atoms coming from two [NiL(solvent)] units coordinate to the central NiII ions. Although different solvents are induced in the complexes, all the NiII ions are six-coordinated and adopt geometries of distorted octahedron. Magnetic measurements were performed on complex 2, an intramolecular antiferromagnetic interaction was observed between NiII ions and a simulation of the experimental data gives J = −2.96 cm−1 and g = 2.30. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Probabilistic Estimate of |Foa| from FEL Data
Crystals 2018, 8(4), 175; https://doi.org/10.3390/cryst8040175
Received: 28 February 2018 / Revised: 27 March 2018 / Accepted: 9 April 2018 / Published: 18 April 2018
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Abstract
The method of the joint probability distribution function was applied in order to estimate the normal structure factor amplitudes of the anomalous scatterer substructure in a FEL experiment. The two-wavelength case was examined. In this, the prior knowledge of the moduli |F
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The method of the joint probability distribution function was applied in order to estimate the normal structure factor amplitudes of the anomalous scatterer substructure in a FEL experiment. The two-wavelength case was examined. In this, the prior knowledge of the moduli | F 1 + | , | F 1 | , | F 2 + | , | F 2 | was used to predict the value of | F 0 a | , which is the structure factor amplitude arising from the normal scattering of the heavy atom anomalous scatterers. The mathematical treatment provides a solid theoretical basis for the RIP (Radiation-damage Induced Phasing) method, which was originally proposed in order to take the radiation damage induced by synchrotron radiation sources into account. This was further adapted to exploit FEL data, where the crystal damage is usually more massive. Full article
Open AccessCommunication Hetero-Trinuclear CoII2-DyIII Complex with a Octadentate Bis(Salamo)-Like Ligand: Synthesis, Crystal Structure and Luminescence Properties
Crystals 2018, 8(4), 174; https://doi.org/10.3390/cryst8040174
Received: 28 March 2018 / Revised: 15 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
A hetero-trinuclear CoII2-DyIII complex, [Co2L(DMF)2Dy(NO3)3]·C2H5O2 was synthesized via the reaction of a multi-naphthol-based bis(Salamo)-like tetraoxime H4L with Co(OAc)2·4H2O and Dy(NO
[...] Read more.
A hetero-trinuclear CoII2-DyIII complex, [Co2L(DMF)2Dy(NO3)3]·C2H5O2 was synthesized via the reaction of a multi-naphthol-based bis(Salamo)-like tetraoxime H4L with Co(OAc)2·4H2O and Dy(NO3)3·6H2O, and fully characterized via elemental analyses, X-ray crystallography, FT-IR and UV-Vis spectra. In addition, luminescence properties of H4L and its CoII2-DyIII complex have also been investigated. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Structures and Fluorescent and Magnetic Behaviors of Newly Synthesized NiII and CuII Coordination Compounds
Crystals 2018, 8(4), 173; https://doi.org/10.3390/cryst8040173
Received: 20 March 2018 / Revised: 15 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
Newly designed three trinuclear coordination compounds [Ni3(L1)2(OAc)2(CH3OH)2] (1), [Ni3(L1)2(OAc)2(CH3CH2CH2OH)2]·2CH3CH2CH
[...] Read more.
Newly designed three trinuclear coordination compounds [Ni3(L1)2(OAc)2(CH3OH)2] (1), [Ni3(L1)2(OAc)2(CH3CH2CH2OH)2]·2CH3CH2CH2OH (2) and [Ni3(L1)2(OAc)2(DMF)2]·1.71DMF (3) and one mononuclear coordination compound [Cu(L2)2] (4) have been synthesized by H2L1 and nickel(II) and copper(II) acetate hydrates in different solvents. Single-crystal X-ray structure determinations revealed that the coordination compounds 13 have analogous molecular structures. The coordination compounds 1, 2, and 3 were affected by the coordinated methanol, n-propanol, and N,N-dimethylformamide molecules, respectively, and the various coordinated solvent molecules give rise to the formation of the representive solvent-induced NiII coordination compounds. All the NiII atoms are six-coordinated with geometries of slightly distorted octahedron. Obviously, in the coordination compound 4, the expected salamo-like mono- or tri-nuclear CuII coordination compound has not been obtained, but a new CuII coordination compound [Cu(L2)2] has been gained. The Cu1 atom is four-coordinated and possesses a geometry of slightly distorted planar quadrilateral. Furthermore, the fluorescence properties of coordination compounds 14 and magnetic behavior of coordination compound 1 were investigated. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessCommunication Crystal Structure of the Catalytic Domain of MCR-1 (cMCR-1) in Complex with d-Xylose
Crystals 2018, 8(4), 172; https://doi.org/10.3390/cryst8040172
Received: 4 March 2018 / Revised: 12 April 2018 / Accepted: 14 April 2018 / Published: 17 April 2018
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Abstract
The polymyxin colistin is known as a “last resort” antibacterial drug toward pandrug-resistant enterobacteria. The recently discovered plasmid-encoded mcr-1 gene spreads rapidly across pathogenic strains and confers resistance to colistin, which has emerged as a global threat. The mcr-1 gene encodes a phosphoethanolamine
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The polymyxin colistin is known as a “last resort” antibacterial drug toward pandrug-resistant enterobacteria. The recently discovered plasmid-encoded mcr-1 gene spreads rapidly across pathogenic strains and confers resistance to colistin, which has emerged as a global threat. The mcr-1 gene encodes a phosphoethanolamine transferase (MCR-1) that catalyzes the transference of phosphoethanolamine to lipid A moiety of lipopolysaccharide, resulting in resistance to colistin. Development of effective MCR-1 inhibitors is crucial for combating MCR-1-mediated colistin resistance. In this study, MCR-1 catalytic domain (namely cMCR-1) was expressed and co-crystallized together with d-xylose. X-ray crystallographic study at a resolution of 1.8 Å found that cMCR-1-d-xylose co-crystals fell under space group P212121, with unit-cell parameters a = 51.6 Å, b = 73.1 Å, c = 82.2 Å, α = 90°, β = 90°, γ = 90°. The asymmetric unit contained a single cMCR-1 molecule complexed with d-xylose and had a solvent content of 29.13%. The structural model of cMCR-1-d-xylose complex showed that a d-xylose molecule bound in the putative lipid A-binding pocket of cMCR-1, which might provide a clue for MCR-1 inhibitor development. Full article
(This article belongs to the Special Issue Biological Crystallization)
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Open AccessReview Optoelectronics Based Dynamic Advancement of Graphene: Characteristics and Applications
Crystals 2018, 8(4), 171; https://doi.org/10.3390/cryst8040171
Received: 28 February 2018 / Revised: 11 April 2018 / Accepted: 12 April 2018 / Published: 17 April 2018
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Abstract
Graphene has impressive features that make it an exceptional material for sophisticated applications in next generation electronics and opto-electronics devices. This peremptory material has attracted researchers’ attention in various fields of recent advancement since its discovery in 2004. Its applied fields are increasing
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Graphene has impressive features that make it an exceptional material for sophisticated applications in next generation electronics and opto-electronics devices. This peremptory material has attracted researchers’ attention in various fields of recent advancement since its discovery in 2004. Its applied fields are increasing day by day. This two-dimensional material (2D) is using mellifluously for the development in different types of devices in the field of optics, photonics, light emitting diode (LED), medical diagnosis, sensing, and so on. In this review, the relevant optical properties and the applications areas with available results in various fields are discussed. Again, the optical conductivity of strained graphene is reviewed in a wavelength related regime that depends on strain modulus and position with field arrangements. Graphene shows a saturation and reverse saturation process due to the increase of light intensity. In addition, strong absorption is observed from the visible to mid-infrared (MIR) wavelength range. Moreover, the application areas of graphene including optics, photonics, plasmonics, mode-locked laser, optical modulator, etc., and the comparison of various results obtained from different sources are presented. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle Quasi-Equilibrium, Multifoil Platelets of Copper- and Titanium-Substituted Bismuth Vanadate, Bi2V0.9(Cu0.1−xTix)O5.5−δ, by Molten Salt Synthesis
Crystals 2018, 8(4), 170; https://doi.org/10.3390/cryst8040170
Received: 11 March 2018 / Revised: 9 April 2018 / Accepted: 12 April 2018 / Published: 17 April 2018
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Abstract
10% copper-substituted (BiCUVOX/Bi2V0.9Cu0.1O5.5−δ) and 5% copper/titanium double-substituted bismuth vanadate (BiCUTIVOX/Bi2V0.9(Cu0.05Ti0.05)O5.5−δ) platelets were formed by molten salt synthesis (MSS) using a eutectic KCl/NaCl salt mixture. The
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10% copper-substituted (BiCUVOX/Bi2V0.9Cu0.1O5.5−δ) and 5% copper/titanium double-substituted bismuth vanadate (BiCUTIVOX/Bi2V0.9(Cu0.05Ti0.05)O5.5−δ) platelets were formed by molten salt synthesis (MSS) using a eutectic KCl/NaCl salt mixture. The product was phase-pure within the limits of X-ray diffraction. The size and form of the platelets could be controlled by changing the heating temperature and time. The crystallite growth rate at a synthesis temperature of 650 °C and the activation energy for grain growth were determined for BICUTIVOX, which experienced inhibited growth compared to BICUVOX. Quasi-equilibrium, multifoil shapes consisting of lobes around the perimeter of the platelets were observed and explained in the context of relative two-dimensional nucleation and edge growth rates. Full article
(This article belongs to the Special Issue Ceramic Conductors)
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Open AccessArticle Crystal Structure, Spectroscopic Investigations, and Physical Properties of the Ternary Intermetallic REPt2Al3 (RE = Y, Dy–Tm) and RE2Pt3Al4 Representatives (RE = Tm, Lu)
Crystals 2018, 8(4), 169; https://doi.org/10.3390/cryst8040169
Received: 1 March 2018 / Revised: 9 April 2018 / Accepted: 10 April 2018 / Published: 16 April 2018
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Abstract
The REPt2Al3 compounds of the late rare-earth metals (RE = Y, Dy–Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt2Al3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c
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The REPt2Al3 compounds of the late rare-earth metals (RE = Y, Dy–Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt2Al3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c = 413.04(2) pm, wR2 = 0.0780, 942 F2 values, 46 variables) with space group Cmmm (oC48; q2pji2hedb). A comparison with the Pearson database indicated that YPt2Al3 forms a new structure type, in which the Pt and Al atoms form a [Pt2Al3]δ polyanion and the Y atoms reside in the cavities within the framework. Via a group-subgroup scheme, the relationship between the PrNi2Al3-type structure and the new YPt2Al3-type structure was illustrated. The compounds with RE = Dy–Tm were characterized by powder X-ray diffraction experiments. While YPt2Al3 is a Pauli-paramagnet, the other REPt2Al3 (RE = Dy–Tm) compounds exhibit paramagnetic behavior, which is in line with the rare-earth atoms being in the trivalent oxidation state. DyPt2Al3 and TmPt2Al3 exhibit ferromagnetic ordering at TC = 10.8(1) and 4.7(1) K and HoPt2Al3 antiferromagnetic ordering at TN = 5.5(1) K, respectively. Attempts to synthesize the isostructural lutetium compound resulted in the formation of Lu2Pt3Al4 (Ce2Ir3Sb4-type, Pnma, a = 1343.4(2), b = 416.41(8), c = 1141.1(2) pm), which could also be realized with thulium. The structure was refined from single-crystal data (wR2 = 0.0940, 1605 F2 values, 56 variables). Again, a polyanion with bonding Pt–Al interactions was found, and the two distinct Lu atoms were residing in the cavities of the [Pt3Al4]δ framework. X-ray photoelectron spectroscopy (XPS) measurements were conducted to examine the electron transfer from the rare-earth atoms onto the polyanionic framework. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Epitaxial Crystallization of Precisely Methyl-Substituted Polyethylene Induced by Carbon Nanotubes and Graphene
Crystals 2018, 8(4), 168; https://doi.org/10.3390/cryst8040168
Received: 9 March 2018 / Revised: 11 April 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
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Abstract
How large of a substituent/branch a polyethylene possesses that can still be induced by nanofillers to form ordered chain structures is interesting, but uncertain. To solve this problem, precisely methyl-substituted polyethylene (PE21M) was chosen as a model to prepare its one-dimensional and two-dimensional
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How large of a substituent/branch a polyethylene possesses that can still be induced by nanofillers to form ordered chain structures is interesting, but uncertain. To solve this problem, precisely methyl-substituted polyethylene (PE21M) was chosen as a model to prepare its one-dimensional and two-dimensional nanocomposites with carbon nanotubes (CNTs) and graphene via solution crystallization. It is shown that kebab-like and rod-like nanofiller-induced crystals were separately observed on the surfaces of CNTs and graphene and the density of rod-like crystals is significantly less than kebab-like ones. The results of differential scanning calorimetry (DSC) and X-ray diffraction (XRD) reveal that CNTs and graphene cannot induce polymers with the substituent volume greater than, or equal to, 2 Å (methyl) to form ordered lattice structure, but CNTs exhibit the better nucleation effect, providing us with guidance to manipulate the physical performance of polymer composites on the basis of the size of the substituent and the type of nanofiller. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle The Influence of Hydroxyl Groups on Friction of Graphene at Atomic Scale
Crystals 2018, 8(4), 167; https://doi.org/10.3390/cryst8040167
Received: 21 March 2018 / Revised: 10 April 2018 / Accepted: 13 April 2018 / Published: 16 April 2018
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Abstract
Hydroxyl groups play an important role in friction of graphene oxides. In this paper, the influence of hydroxyl groups on friction of graphene is investigated by molecular dynamics simulation. The results show that the friction does not always go up with the rising
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Hydroxyl groups play an important role in friction of graphene oxides. In this paper, the influence of hydroxyl groups on friction of graphene is investigated by molecular dynamics simulation. The results show that the friction does not always go up with the rising of hydroxyl groups ratio, and reaches the maximum when the hydroxyl groups ratio between interfaces is about 10%. The reason is that hydrogen bonds tend to form in interlayers when the hydroxyl groups ratio is high. The formed hydrogen bonds between interfaces are closely related to the friction. However, the analysis of the component of van der Waals, Coulomb’s forces and hydrogen bonds interaction between interfaces indicates that van der Waals forces are dominant in friction, which can be attributed to the influence of interface distance on friction. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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