Physical Properties of Engineered Nanocomposites for Defense Applications

Polymer nanocomposites are significant for modern and future technologies (aerospace, defense, water purification etc.) due to their tailored properties, lightweight and low cost. However, ‘forward’ engineered polymer (host matrix) composites with smaller size nanoparticles (guest) providing desired properties targeting specific applications remains a challenging task as they depend largely on nanoparticles size, shape and loading (volume fraction). This study develops polymer nanocomposites impregnated with ‘organic-inorganic’ silsesquioxane nanoparticles and graphene nanoribbons, and investigates microscopic structure and dynamics of interfacial layer to predict macroscale properties. The nanocomposites consist of poly(2-vinylpyridine) (P2VP) polymer (segment ~5nm) with spherical silsesquioxane nanoparticles (diameter ~2-5nm) and planar nitrogenated graphene nanoribbons (lateral dimension ~5-10 nm), both with attractive (hydrogen bonding and electrostatic) interactions. This approach reinforces the role of molecular parameters controlling the structure and dynamics of interfacial layer in predicting properties. The transmission electron microscopy will reveal microscopic structure and the lattice bonding, interfacial stress transfer and conjugation length are determined from micro-Raman spectroscopy. The glass transition temperature, Tg, obtained using differential scanning calorimetry reveals positive shift in Tg values with nanoparticles loadings. We used temperature dependent broadband dielectric spectroscopy to gain fundamental insights into the interfacial layer and diffusion dynamics above and below Tg and to establish quantitative microstructure-property correlations. KY NSF EPSCoR REG funding is acknowledged

Multifunctional nanodiamond surfaces functionalization for developing [abstract]

Abstract only availableSince 9/11 attack and the deaths from anthrax contamination, bio-safety issues have become prominent. Food safety, on the other hand, especially with regard to foodborne pathogens, is another important issue. Therefore, the rapid or real time detection of pathogens becomes extremely important for the food industry as well as homeland security. Among the family of advanced carbon materials, diamond is of great interest owing to their several unsurpassable physical (mechanical, electrical, thermal, and chemical/biological inertness) properties for various applications. In this work, the potential of the diamond surfaces in the development of next generation 'smart' biosensing platforms have been investigated and we have used three variants of diamond surfaces: nanodiamond, ultradispersed diamond and adamantane. Our goal is to immobilize the antibodies and bacterial (bio-molecules) binding on the plasma modified diamond surfaces to increase their efficacy as potential biosensors by researching the antibody-antigen binding to increase detection and sensitivity. The efficiency of the bio-functionalization will be assessed through various complementary structural and optical tools: electron and inverted optical microscopy, fluorescence emission and Raman spectroscopy, and UV/Vis. The present work will discuss our findings in terms of: a) the significance of nanodiamond surfaces and plasma treatment; b) the efficacy and efficiency of covalent binding of biomolecules and c) the specificity of antibodies which may enhance the efficiency of bio-detection through uniform distribution. This work is supported in parts by internal BBC MU and S. Gupta's startup funds.College of Engineering Undergraduate Research Option; BBC MU; Dr. Sanju Gupt

Elucidating the effects of oxygen- and nitrogen-containing functional groups in graphene nanomaterials for applied electrochemistry by density functional theory

Graphene nanomaterials functionalized with oxygen groups [graphene oxide (GO) and reduced GO (rGO)] are either doped with element nitrogen or nitrogen-containing aromatic moieties followed by the investigation of electrochemical properties that generally show enhanced electroanalytical performance. We studied structural, morphological, and physical–chemical properties using correlative techniques. While we attribute their improved properties promoted simultaneously by topologically interconnected mesoporous network morphology, the presence of heteroatom species, and lattice vibrational structure, the complex interpretation requires the need to supplement the experimental observations with theoretical calculations for further insights. The complex interplay of pore size and redox properties revealing distinctive supercapacitive (ion-adsorption controlled) and pseudocapacitive (diffusion-controlled) energy storage mechanistic contributions arises from the combined effects of oxygen and nitrogen functional groups, most likely located on the basal plane and at the pore edge plane sites. The density functional theory calculations provided band structure and electron transfer from Mulliken and Hirshfeld population analyses helping discern the nature of various functional groups in diverse graphene. Interestingly, while quaternary (NZQ) and pyridinic-N-oxides (NZO) on the basal planes show enhanced capacitance due to positive charge and thus an improved electron transfer at higher current loads identified in nitrogen-doped aerogel (AG/nitrogenated) and GO-derived rGO by chemical and electrochemical properties, the other important functional groups affecting the energy storage are pyridinic (N-6) and pyrrolic (N-5) nitrogen groups on the edge of the rGO nanosheet in association with carboxylic (ZCOOH) and quinone (CvO) functional groups in nitrogenated functional graphene/graphene aerogel and rGO coated polyaniline, contributing to a pseudocapacitive character

Performance Optimization for Distributed Database Based on Cache Investment

As technology plays important role in every aspect of life especially in the industrial field, a vast amount of data is generated for controlling and monitoring tools and to help in system development. That results in an increased size of data, which affects the speed and performance of applications/programs. Here a design strategy is proposed to show how to improve both the speed and performance of computer applications by improving the performance of database queries. Key factors that determine computer performance (speed and performance of the processor) are the processor speed, the size of RAM, and the cache memory strategy for the processor. In this paper, we are introducing a solution that is proven to be a tool to increase the performance of queries. It will help to enhance the performance of database queries responsiveness irrespective of the database size. The proposed policy is built-up on the caching concepts i.e. cache investment. Cache investment is a method to combine query optimization and data placement. This work on the concept of investment looks beyond the performance of a single query and helps in achieving a better hit ratio in a long term for large database systems. This paper, discuss and explain the design, architecture and working of the proposed policy. The results show how this proposed policy helps in improving the performance of the database, especially relevant for today’s “big data” environment

Electrochemically Desulfurized Molybdenum Disulfide (MoS2) and Reduced Graphene Oxide Aerogel Composites as Efficient Electrocatalysts for Hydrogen Evolution

Recent developments in graphene related materials including molybdenum disulfide (MoS2) is gaining popularity as efficient and cost-effective nanoscale electrocatalyst essential for hydrogen production. These “clean” energy technologies require delicate control over geometric, morphological, chemical and electronic structure affecting physical and electrochemical catalytic properties. In this work, we prepared three-dimensional hierarchical mesoporous aerogels consisting of two-dimensional functionalized graphene and MoS2 nanosheets of varying ratio of components under hydrothermal–solvothermal conditions (P \u3c20 \u3ebar, T \u3c200 \u3e°C). We systematically characterized these hybrid aerogels in terms of surface morphology, microstructure, understand heterointerfaces interaction through electron microscopy, X-ray diffraction, optical absorption and emission and Raman spectroscopy, besides electrochemical properties prior to and post electrochemical desulfurization that induces finely controlled sulfur vacancies. They feature enhanced electrical conductivity by means of eliminating contact resistance and meso-/nanoporous structure facilitating faster ion diffusion (mass transport). We demonstrate that controlled defects density, edges plane sites (nanowalls), mesoscale porosity and topological interconnectedness (monolithic aerogel sheets) invoked can accelerate electrocatalytic hydrogen production. For instance, low over potential with Tafel slope ~77 mV·dec-1 for 60 wt.% MoS2, highcurrent density, and good stability was achieved with desulfurization. These results are compared with continuous multilayer MoS2 films highlighting the multiple role of tunable structure and electronic properties. The adjacent S-vacancy defectsinduced increase in density of states, dissociation and confinement of water molecules at the pore edge and planar S-vacancy sites calculated using density functional theory helped in establishing improved heterogeneous electrocatalytic rate. This is supported with combined measurements of diffusion coefficient and heterogeneous electron transfer rate via surface-sensitive scanning electrochemical microscopy (SECM) technique

Carbon nanotubes and their composites with nanodiamond for thermal packaging: Syntheses, characterization and modeling [abstract]

Abstract only availableIn the family of carbon-based nanosystems, carbon nanotubes (both single- and multi-walled) are cylindrical carbon molecules with many extremely useful properties that make them ideal for use in multitude of technological applications. Owing to their extremely high thermal conductivity properties, nanotubes enable the most potentially efficient heat-transfer applications. The microchip industry would see great benefits for thermal management applications. Nanodiamonds (nano-scale diamond structures), on the other hand are also of great interest have equally reasonable thermal conductivity and a radiation hard material. Combination of nanotubes and nanodiamonds forming truly trigonal-tetragonal composites could provide quite effective heat-transfer plus the added bonus of being radiation resistant for harsh environments such as space. The present research work is designed to measure the thermal conductivities of nanotubes and their composites with nanodiamond following Nielsen method applicable for two-phase systems and well-known Widemann-Franz law determining electronic contribution towards thermal conductivity (kappa_e). This model will allow us to predict the thermal conductivity of nanocomposites that may lie somewhere between the conductivity of the two constituents, following the most versatile Halpin-Tsai equation of phase mixing. Variation of thermal conductivity of these nanocomposites with gamma irradiation is determined following the similar approach as described above. They were analyzed prior to and post-irradiation in terms of morphology, microscopic structure and physical properties using electron microscopy, visible Raman spectroscopy and electrical [I(V)] measurements to establish property-structure-processing relationship.College of Engineering Undergraduate Research Option; MU Research Counci

Two-Dimensional Layered Materials (Graphene-MoS2) Nanocatalysts for Hydrogen Production

Recent development of two-dimensional layered materials including graphene-family and related nanomaterials have arisen as potential game changer for energy, water and sensing applications. While graphene is a form of carbon arranged hexagonally within atomic thin sheet, MoS2 is becoming a popular, efficient, and cost-effective catalyst for electrochemical energy devices, in contrast to expensive platinum and palladium catalysts. In this work, we electrochemically desulfurize few-layer molybdenum disulfide (MoS2) and aerogels with reduced graphene oxide (rGO) prepared under hydrothermal conditions ((P\u3c 20 bar, T\u3c 200 oC), for improving hydrogen evolution reaction (HER) activity via point defects (S-vacancy). Moreover, the interactions between rGO and MoS2 components create emergent heterostructures with desirable physicochemical properties (specific surface area, mechanical strength, faster diffusion, facile electron and ion transport) enabled by chemically bridged (covalently) tailored interfaces. We demonstrate that with an optimized number defect density, particularly by exposing the edges of MoS2 layers and nanowalls in graphene-MoS2 ‘hybrid’ aerogels, interfacial processes during catalytic reactions are accelerated. To understand the effects of defects on HER activity, we varied the applied potential and operating duration for optimized defect density. This study offers a unique method for tuning the properties of layered MoS­2 and hybrids as promising, cost-effective and efficient nanocatalysts and establishes the structure–catalytic activity relationships via scanning electrochemical microscopy at electrode/electrolyte interface besides mapping electrochemical (re)activity and electro-active site distribution

Computational data of molybdenum disulfide/graphene bilayer heterojunction under strain

The data presented in this paper refer to the research article Dry and Hydrated Defective Molybdenum Disulfide/Graphene Bilayer Heterojunction Under Strain for Hydrogen Evolution from Water Splitting: A First-principle Study . Here, we present the Density Functional Theory (DFT) data used to generate optimal geometries and electronic structure for the MoS2/graphene heterostructure under strain, for dry and hydrated pristine and defect configurations. We also report DFT data used to obtain hydrogen Gibbs free energies for adsorption on the MoS2 monolayer and on graphene of the heterostructure. The DFT data were calculated using the periodic DFT code CRYSTAL17, which employs Gaussian basis functions, under the hybrid functionals PBE0 and HSE06. Moreover, we also report the data used for Quantum Theory of Atoms in Molecules (QTAIM) and Non-covalent Interaction (NCI) analysis calculations. These data were obtained using the optimized unit cell configurations from the periodic DFT and inputted to Gamess program, thus generating files that could be read by the Multiwfn program used for QTAIM and NCI calculations

Vanadium pentoxide nanobelt-reduced graphene oxide nanosheet composites as high-performance pseudocapacitive electrodes: Ac impedanc spectroscopy data modeling and theoretical calculations

Graphene nanosheets and graphene nanoribbons, G combined with vanadium pentoxide (VO) nanobelts (VNBs) and VNBs forming GVNB composites with varying compositions were synthesized via a one-step low temperature facile hydrothermal decomposition method as high-performance electrochemical pseudocapacitive electrodes. VNBs from vanadium pentoxides (VO) are formed in the presence of graphene oxide (GO), a mild oxidant, which transforms into reduced GO (rGOHT), assisting in enhancing the electronic conductivity coupled with the mechanical robustness of VNBs. From electron microscopy, surface sensitive spectroscopy and other complementary structural characterization, hydrothermally-produced rGO nanosheets/nanoribbons are decorated with and inserted within the VNBs\u27 layered crystal structure, which further confirmed the enhanced electronic conductivity of VNBs. Following the electrochemical properties of GVNBs being investigated, the specific capacitance Csp is determined from cyclic voltammetry (CV) with a varying scan rate and galvanostatic charging-discharging (V-t) profiles with varying current density. The rGO-rich composite V1G3 (i.e., VO/GO = 1:3) showed superior specific capacitance followed by VO-rich composite V3G1 (VO/GO = 3:1), as compared to V1G1 (VO/GO = 1:1) composite, besides the constituents, i.e., rGO, rGOHT and VNBs. Composites V1G3 and V3G1 also showed excellent cyclic stability and a capacitance retention of \u3e80% after 500 cycles at the highest specific current density. Furthermore, by performing extensive simulations and modeling of electrochemical impedance spectroscopy data, we determined various circuit parameters, including charge transfer and solution resistance, double layer and low frequency capacitance, Warburg impedance and the constant phase element. The detailed analyses provided greater insights into physical-chemical processes occurring at the electrode-electrolyte interface and highlighted the comparative performance of thin heterogeneous composite electrodes. We attribute the superior performance to the open graphene topological network being beneficial to available ion diffusion sites and the faster transport kinetics having a larger accessible geometric surface area and synergistic integration with optimal nanostructured VO loading. Computational simulations via periodic density functional theory (DFT) with and without V2O5 adatoms on graphene sheets are also performed. These calculations determine the total and partial electronic density of state (DOS) in the vicinity of the Fermi level (i.e., higher electroactive sites), in turn complementing the experimental results toward surface/interfacial charge transfer on heterogeneous electrodes

Dataset of optical and electronic properties for MoS BrowZine Journal Cover 2-graphene vertical heterostructures and MoS2-graphene-Au heterointerfaces

The computational and experimental data presented in this paper refer to the research article First-Principles Calculations Integrated with Experimental Optical and Electronic Properties for MoS2-graphene Heterostructures and MoS2-graphene-Au Heterointerfaces . The computational data includes structural information, electronic and optical properties, and data to calculate the work functions for various molybdenum disulfide and graphene heterostructures and their heterointerfaces with gold. The optical properties calculations include the frequency-dependent dielectric function, the refractive index, the reflectivity, the extinction coefficient, and the energy loss function. These properties were calculated using the independent particle approximation (IPA). As for the experimental optoelectronic properties, we measured photoluminescence spectra (optical), Raman spectra (vibrational), work function (surface electronic property), and local photoconductivity (semiconducting behavior) of graphene-MoS2 heterointerfaces in addition to individual graphene and MoS2 layers on gold. The variation in the exciton bands, the Raman bands, and in the average work function elucidated the semiconducting n-p junction behavior