Engineering Mesophase Stability and Structure via Incorporation of Cyclic Terminal Groups

We report on the characterisation of a number of liquid-crystalline materials featuring cyclic terminal groups, which lead to significant enhancements in the temperature range of the mesomorphic state. Materials with only short terminal chains are able to support lamellar mesophase formation by appending a large terminal cyclic unit at the end of a short methylene spacer. X-ray scattering experiments reveal that the layer spacings of the lamellar smectic phase are significantly larger when a cyclic end-group is present than for equivalent linear unsubstituted materials, but there is no effect on orientational order. Fully atomistic molecular dynamics simulations faithfully reproduce experimental layer spacings and orientational order parameters, and indicate that the cyclic terminal units spontaneously segregate into diffuse sub-layers and thus cause the increased layer spacing. This shape segregation predicted by molecular dynamics simulations is observed in the crystalline solid state by X-ray diffraction.

Effects of Air Holes in the Cladding of Photonic Crystal Fibers on Dispersion and Confinement Loss of Orbital Angular Momentum Modes

In the development of orbital angular momentum (OAM) mode division multiplexing (MDM), the capacity of optical fiber communication must be improved. However, owing to dispersion and confinement loss, many OAM modes do not propagate stably over a long distance in optical fibers. In this work, the effects of the size, number, shape, number of layers, and layer spacing of air holes in the cladding of the fiber on the dispersion and confinement loss are analyzed based on a simple structure. The trends are studied and summarized to facilitate the design of optical fibers to achieve stable transmission of OAM modes over a long distance.

Electrochemical Performance of Delafossite, AgFeO2: A Pseudo-Capacitive Electrode in Neutral Aqueous Na2SO4 Electrolyte

Layered delafossite AgFeO2 with open channel structure is envisaged as a pseudo capacitor electrode using Fe2+/ Fe3+ redox couple. A simple co-precipitation method was employed for the phase formation of delafossite AgFeO2 resulting in a mixture of 2H and 3R-phase. Phase tuning of 2H phase was done by controlling the calcination conditions and characterizing by powder XRD, FT-IR, and Raman methods. 2H AgFeO2 was used to synthesize as a majority phase because it have the larger inter layer spacing than 3R phase shown. HRTEM study confirms the formation 2H phase in majority. All of the synthesized samples exhibit predominantly faradic battery-type redox behavior along with surface charge storage. Flower like microarchitectures of AgFeO2 show outstanding electrochemical performance with high specific capacity of 110.4 F/g at 1 A/g current density, that retained up to 89% after 2000th times charge/discharge in 1M Na2SO4 electrolyte. In an asymmetric device mode, AFO-400//AC full cell exhibits superior electrochemical performance by delivering high energy density (33.5 Wh/kg) and high power density (454.3 W/kg) with excellent cycling stability (86% retention after 2000th cycles). The results clearly demonstrate that the synthesized delafossite AgFeO2 containing mixture of 2H and 3R-phases have remarkable potential to be used as a negative electrode material for supercapacitor and other energy storage technologies

Photocatalytic application of Graphene oxide-ZnO nanocomposite for the reduction of methylene blue dye

The Graphene Oxide (GO) and GO-Zinc Oxide (GO-ZnO) nanocomposite were prepared using simplified techniques with modified Hummer’s and solvothermal methods for photocatalytic application. In a comparative study, the optimized geometries, binding energies, electronic properties, non-linear optical properties and density of states of GO-ZnO were calculated using density functional theory (DFT) calculations with B3LYP method at 6-31G (d,p) and LanL2DZ basis sets to examine the binding site of a methylene blue (MB) dye systematically. The result of Natural bond orbital (NBO) analysis revealed the effective charge transfer and also explained the mechanism and efficiency of the photocatalytic activity of GO-ZnO. Density of states supported the strong interaction of MB with the GO-ZnO leading to the degradation of the MB dye. The attained theoretical results depict the existence of n → σ*, n → n* and σ → σ* interactions, improved charge transfer, reduced band gap which establish the use of GO-ZnO in the visible light photocatalytic performance. Characterization methods such as XRD, FTIR and UV were carried out to support our theoretical results. The XRD results confirmed the particle size of 21 nm with inter layer spacing of 0.87 nm. FTIR spectroscopy indicated the characteristic bands related to the elements in GO-ZnO. The higher electrical conductivity is studied using UV-Vis spectral analysis. The calculated results show good agreements with experimental observations reveal that the GO-ZnO has good photocatalytic behavior.

Accessing Structural, Electronic, Transport and Mesoscale Properties of Li-GICs via a Complete DFTB Model with Machine-Learned Repulsion Potential

Lithium-graphite intercalation compounds (Li-GICs) are the most popular anode material for modern lithium-ion batteries and have been subject to numerous studies—both experimental and theoretical. However, the system is still far from being consistently understood in detail across the full range of state of charge (SOC). The performance of approaches based on density functional theory (DFT) varies greatly depending on the choice of functional, and their computational cost is far too high for the large supercells necessary to study dilute and non-equilibrium configurations which are of paramount importance for understanding a complete charging cycle. On the other hand, cheap machine learning methods have made some progress in predicting, e.g., formation energetics, but fail to provide the full picture, including electrostatics and migration barriers. Following up on our previous work, we deliver on the promise of providing a complete and affordable simulation framework for Li-GICs. It is based on density functional tight binding (DFTB), which is fitted to dispersion-corrected DFT data using Gaussian process regression (GPR). In this work, we added the previously neglected lithium–lithium repulsion potential and extend the training set to include superdense Li-GICs (LiC6−x; x>0) and lithium metal, allowing for the investigation of dendrite formation, next-generation modified GIC anodes, and non-equilibrium states during fast charging processes in the future. For an extended range of structural and energetic properties—layer spacing, bond lengths, formation energies and migration barriers—our method compares favorably with experimental results and with state-of-the-art dispersion-corrected DFT at a fraction of the computational cost. We make use of this by investigating some larger-scale system properties—long range Li–Li interactions, dielectric constants and domain-formation—proving our method’s capability to bring to light new insights into the Li-GIC system and bridge the gap between DFT and meso-scale methods such as cluster expansions and kinetic Monte Carlo simulations.

Effects of long-term flue gas exposure on chemical-structural properties of South African coals: perspective on advanced analytical techniques

The sequestration of carbon dioxide (CO 2 ) in unmineable coal seams is one of the geologic options earmarked to alleviate the emissions of the greenhouse gases to the atmosphere. Direct flue gas injection into unmineable coal seams has been considered to partially offset the cost of the utilizing this technology. This paper presents findings of the evolution of chemical structural properties of two South African coals from Somkhele (Coal SML) and Ermelo (Coal EML) coalfields after long-term (2 232 hours) flue gas exposure by applying advanced analytical techniques. The two coal samples were exposed to a synthetic flue gas simulating coal-fired power plant gas emissions containing 12% CO 2 , 5.5% O 2 , 82% N 2 , 0.38% SO 2 , and 0.12% NO 2 under in-seam temperature and pressure conditions of 60 °C and 9.0 MPa, respectively. The advanced analytical techniques applied included universal attenuated total reflectance-Fourier transform infrared (UATRFTIR), carbon-13 solid state nuclear magnetic resonance spectroscopy ( 13 C ss NMR), and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX) wide-angle X-ray diffraction (WAXRD). The UATR-FTIR spectra revealed weakened C─H, aliphatic C─C, C─O, ─OH, and out-of-plane aromatic C─H functional groups. The results from the treated coals of 13 C ss NMR for the structural parameters show notable changes in the oxygen functionalities reporting the aliphatic carbon bonded to oxygen, 𝑓 𝑎𝑙 𝑂 , while the WAXRD data showed some significant changes in the inter-layer spacing and the crystalline diameter as compared to the untreated coals.

Texture and Microstructure Evolution of Ultra-High Purity Cu-0.1Al Alloy under Different Rolling Methods

The microstructure and texture distribution of ultra-high purity Cu-0.1Al alloy target play a key role in the quality of the sputtering film. The Cu-0.1Al alloy sheets were processed by unidirectional (UR) and cross rolling (CR), and X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) technologies were adopted to observe the texture and microstructure evolution. XRD results reveal that the texture types vary greatly in UR and CR due to the change of strain path. As the strain increases to 90%, S texture occupies the most, followed by copper texture in the UR sample, while brass texture dominates the most in the CR sample. Additionally, the orientation density of texture does not increase significantly with the increase of strain but shows a downward trend both in UR and CR modes. EBSD analysis demonstrates that compared with UR, the deformation microstructure in CR is more uniform, and the layer spacing between the deformation bands is smaller, which can reduce the local-region stress concentration. After the completion of recrystallization, the difference in average grain size between the UR and CR-annealed samples is not significant, and the recrystallized grains become much finer with the increase of strain, while more equiaxed grains can be observed in CR-annealed samples.