Three-dimensional Dendritic Structures Research Articles

Study of hydrogen absorption in a novel three-dimensional graphene structure: Towards hydrogen storage applications

The use of a novel three-dimensional graphene structure allows circumventing the limitations of the two-dimensional nature of graphene and its application in hydrogen absorption. Here we investigate hydrogen-bonding on monolayer graphene conformally grown via the epitaxial growth method on the (0001) face of a porousified 4H-SiC wafer. Hydrogen absorption is studied via Thermal Desorption Spectroscopy (TDS), exposing the samples to either atomic (D) or molecular (D2) deuterium. The graphene growth temperature, hydrogen exposure temperature, and the morphology of the structure are investigated and related to their effect on hydrogen absorption. The three-dimensional graphene structures chemically bind atomic deuterium when exposed to D2. This is the first report of such an event in unfunctionalized graphene-based materials and implies the presence of a catalytic splitting mechanism. It is further shown that the three-dimensional dendritic structure of the porous material temporarily retains the desorbed molecules and causes delayed emission. The capability of chemisorbing atoms after a catalytic splitting of hydrogen, coupled to its large surface-to-volume ratio, make these structures a promising substrate for hydrogen storage devices.

Branched polybenzimidazole / polymeric ionic liquid cross-linked membranes with high proton conductivity and mechanical properties for HT-PEM applications

Branched polymers have unique three-dimensional dendritic structures, so they have received a lot of attention in the application of high temperature proton exchange membranes. In this work, we synthesize BOPBI-X (X = 3%, 6%, 9%) membranes with different branched ratios based on the synthesis of OPBI, due to the introduction of a rigid triazine structure with a larger free volume, the membranes could absorb more phosphoric acid (PA) while maintaining sufficient mechanical strength. Among them, the BOPBI-6% membrane obtains splendid comprehensive performance, when the PA doping level (ADL) is 9.55, it achieves a proton conductivity of 99.2 mS cm−1 at 180 °C, which is 1.8 times higher than OPBI (54.8 mS cm−1), and it performs well in long-term oxidation stability test after 144 h, it still has a mass retention rate of 90%. For the sake of further boost the performance of the membrane, cross-linkable polymeric ionic liquid (PIL) is introduced to the system. Among them, BOPBI-PIL-30% membrane has sufficient mechanical properties (5.50 ± 0.8 MPa), and the proton conductivity (146.9 mS cm−1) at 180 °C is also excellent, so BOPBI-PIL-30% membrane is expected to be a promising candidate as HT-PEMs.

Volume Overlap Variation within Hyperbranched Polymer Brushes Resolves Topology Effects against Protein Fouling.

Hyperbranched polymer brushes with a three-dimensional dendritic structure are used in antifouling applications to obtain bioinert and compact dendritic structures. Though hyperbranched polyglycerol (HPG) is extensively utilized in the antifouling layer, there is still a lack of direct studies on the relationship between the interfacial properties and topology effect of hyperbranched polymer brushes. Here, we established the degree of chain volume overlap (Dv) to characterize the spatial shielding efficiency generated by HPG brushes and investigated the impact mechanism of the variable chain length on the interfacial physicochemical properties. The results revealed the Dv-relevant feature of performance that the most densely packed HPG brushes for a medium-length LHPG3.07 enable the functional surface to display optimal antifouling performance toward protein adsorption by forming the most effective space barrier and hydrated layer in appropriate molecular weights and graft density. Moreover, we clarified the advance of hyperbranched polymer brushes exhibited in topology effects for imparting surface-enhanced resistance to biofouling relies on the generable higher steric hindrance as compared with linear analogs. This study established a Dv-relevant evaluation model for acquiring an optimized antifouling surface based on the appropriate choice of polymer structure, topology morphologies, and grafting parameters.

Exfoliation of bimetallic (Ni, Co) carbonate hydroxide nanowires by Ar plasma for enhanced oxygen evolution.

Efficient bimetallic (Ni, Co) carbonate hydroxide (NiCo-LDHs) electrocatalysts for the oxygen evolution reaction were prepared using an Ar plasma exfoliation strategy. Smooth 1D nanowires of NiCo-LDHs were delaminated into thin nanosheets to form three-dimensional dendritic structures. Furthermore, the electrochemical active surface area was significantly increased and more higher oxidation states were exposed during this process. The exfoliated NiCo-LDHs exhibited a lower onset potential, much higher current density and longer stability.

Construction of dendritic structure by nano-SiO2 derivate grafted with hyperbranched polyamide in aramid fiber to simultaneously improve its mechanical and compressive properties

Weak transverse interaction of aramid fiber leads to low compressive strength, which is a prominent problem for its further application. In this study, a novel strategy by constructing dendritic structure in aramid fiber was conducted to solve the problem. Hyperbranched aromatic polyamide and linear aromatic polyamide are grafted on nano-SiO2 respectively, which will present absolutely different conformations. Structure of the SiO2 derivates was analyzed in detail by Fourier transform infrared spectroscopy (FTIR), dynamic laser scattering (DLS) and X-ray photoelectron spectroscopy (XPS). Compared with linear polyamide, hyperbranched polyamide tends to grow in multiple directions during polymerization due to significant steric effect, which can be confirmed by molecular simulation. When the SiO2 derivates were blended in aramid fiber, three-dimensional dendritic structure will be constructed by utilizing distinctive conformation of the hyperbranched polyamide. When loading content of nano-SiO2 derivate modified by hyperbranched polyamide in aramid fiber is 0.5 wt%, compressive strength of the fiber is improved by nearly 114%. Moreover, tensile strength and modulus are improved by nearly 13% and 9% respectively. Therefore, comprehensive performance of the aramid fiber can be remarkably improved by utilizing unique conformation of the hyperbranched polyamide, even if loading content of the SiO2 derivate is relatively low.

Three-Dimensional Dendritic Structures of NiCoMo as Efficient Electrocatalysts for the Hydrogen Evolution Reaction.

First-row (3d) transition-metal catalysts, such as bimetallic Ni-Co, represent an emerging class of electrocatalysts for HER, but they usually suffer from a large overpotential significantly above thermodynamic demands. Here, we doped NiCo catalyst with non3d metals molybdenum (Mo) for improvement in catalyzing the hydrogen evolution reaction. The ternary catalyst was readily obtained by a one-pot process via the sequential electrodeposition of Ni, Co, and Mo precursors on titanium (Ti) support. By tailing the deposition conditions, we fabricated NiCoMo catalysts with three-dimensional dendritic structures, exhibiting large amounts of electrochemically active sites. To attain the benchmark HER current density of -10 mA cm-2, an overpotential of ∼132 mV is required in 0.1 M KOH for the Mo-doped NiCo (5 atom % Mo in bath), and they produced the decreasing in Tafel slope of ∼108 mV decade-1 exceeding those of binary NiCo alloy catalysts and other contents of Mo doping. In a synergistic effect, dopant incorporation of Mo element may provide near-optimal adsorption energies for HER intermediates promoting the process of water dissociation and hydrogen intermediates production and binding into molecular hydrogen.

Dendritic CuO structures synthesized by bipolar electrochemical process for electrochemical energy storage

Cupric oxide is an inexpensive material with electrochemical behavior that can be used for energy storage applications. Here, we prepare CuO materials by a simple bipolar electrochemical process in deionized water, where a high voltage is applied between two stainless steel feeding electrodes symmetrically surrounding an electrically floating copper plate. CuO is mainly formed in the locally alkaline region facing the anodic pole of the copper plate, where electro-dissolved Cu2+ undergo successive reactions of complexation–dehydration with OH− ions. The morphology, composition, and phase structure of as-prepared materials were characterized by scanning electron microscopy, powder X-ray diffraction, micro-Raman spectroscopy, and Vis-near-IR spectroscopy. We have found that CuO materials are self-assembled in three-dimensional dendritic structures that can grow up to millimeters in size. The electrochemical characterization in 1molL−1 KOH by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy shows a capacitive behavior of CuO structures, with an average capacitance value reaching 202Fg−1 at 10Ag−1, giving an energy density of 7.0Whkg−1 for a power density of 2.5kWkg−1. At 20Ag−1 current density, the materials exhibit 90% capacitance retention over 2000 charge/discharge cycles with a coulombic efficiency exceeding 95%.

Fluid Flow and Defect Formation in the Three-Dimensional Dendritic Structure of Nickel-Based Single Crystals

Fluid flow within the dendritic structure at the solid–liquid interface in nickel-based superalloys has been studied in two directionally solidified alloy systems. Millimeter-scale, three-dimensional (3D) datasets of dendritic structure have been collected by serial sectioning, and the reconstructed mushy zones have been used as domains for fluid-flow modeling. Flow permeability and the influence of dendritic structure on flow patterns have been investigated. Permeability analyses indicate that the cross flow normal to the withdrawal direction limits the development of flow instabilities. Local Rayleigh numbers calculated using the permeabilities extracted from the 3D dataset are higher than predicted by conventional empirical calculations in the regions of the mushy zone that are prone to the onset of convective instabilities. The ability to measure dendrite surface area in 3D volumes permit improved prediction of permeability as well.

Testing the accuracy of absolute intensity estimates of the ancient geomagnetic field using copper slag material

The Middle-Eastern copper slag is a promising new material for studying intensity variations in the geomagnetic field with high resolution and precision. The purpose of this study is to test the accuracy of archaeointensity estimates determined using copper slag by addressing two questions: 1) “Does slag material display the magnetic properties required for valid Thellier experiments?” and 2) “What is the accuracy of the archaeointensity estimates derived from Thellier-style experiments on optimal samples?” We address the first question through a comprehensive microscopic and magnetic study of representative archaeological slag samples in order to identify the properties responsible for optimal behavior in Thellier experiments. To address the second question, we reproduced slag samples in the laboratory under controlled magnetic fields and analyzed them using the same IZZI paleointensity technique used for the ancient slag. Microscopic analyses of the archaeological slag show that ferromagnetic phases occur as three-dimensional dendritic structures whose branches consist of submicron-elongated particles. Magnetic analyses show that these dendrites behave as an assemblage of shape-controlled, single-domain-like particles and that their magnetization is thermoremanent. We conclude that slag material can be magnetically suitable for valid Thellier experiments. The laboratory-produced slag material demonstrated similar magnetic and mineralogical properties as the archaeological slag. IZZI experiments showed that non-linear TRM acquisition, even at field strengths similar to Earth's, and TRM anisotropy are important factors to monitor during paleointensity studies of slag material. Anisotropy and non-linearity are probably related to the dendritic shape of the oxide grains. Intensity estimates derived from three laboratory-produced slag samples demonstrated accuracy to within ∼ 5% after applying the required corrections.

Height-controlled nanowire branches on nanotrees using a polymer mask

The production of complex three-dimensional dendritic structures is an important step inthe application of semiconductor nanowires. One promising method for achieving this is thesequential seeding of multiple generations of epitaxial nanowires using metal seed particles.However, it is difficult to control and predict the position of second and higher generationnanowires with respect to the first generation. Here we demonstrate a procedure forcontrolling the position of second-generation epitaxial nanowire branches on verticallyaligned nanowire trunks. This method uses a spun-on polymer layer that masksfirst-generation wires to a specified height, preventing the growth of nanowire branches atlower positions as well as new nanowire growth on the substrate. This methodappears not to be dependent on the materials or growth system (in this caseMOVPE-grown GaP is demonstrated), and hence is likely to be applicable to avariety of materials systems and growth procedures using metal seed particles.

Computer generation and quantitative morphometric analysis of virtual neurons.

An important goal in computational neuroanatomy is the complete and accurate simulation of neuronal morphology. We are developing computational tools to model three-dimensional dendritic structures based on sets of stochastic rules. This paper reports an extensive, quantitative anatomical characterization of simulated motoneurons and Purkinje cells. We used several local and global algorithms implemented in the L-Neuron and ArborVitae programs to generate sets of virtual neurons. Parameters statistics for all algorithms were measured from experimental data, thus providing a compact and consistent description of these morphological classes. We compared the emergent anatomical features of each group of virtual neurons with those of the experimental database in order to gain insights on the plausibility of the model assumptions, potential improvements to the algorithms, and non-trivial relations among morphological parameters. Algorithms mainly based on local constraints (e.g., branch diameter) were successful in reproducing many morphological properties of both motoneurons and Purkinje cells (e.g. total length, asymmetry, number of bifurcations). The addition of global constraints (e.g., trophic factors) improved the angle-dependent emergent characteristics (average Euclidean distance from the soma to the dendritic terminations, dendritic spread). Virtual neurons systematically displayed greater anatomical variability than real cells, suggesting the need for additional constraints in the models. For several emergent anatomical properties, a specific algorithm reproduced the experimental statistics better than the others did. However, relative performances were often reversed for different anatomical properties and/or morphological classes. Thus, combining the strengths of alternative generative models could lead to comprehensive algorithms for the complete and accurate simulation of dendritic morphology.

Variability and Invariability in the Structure of an Identified Nonspiking Interneuron of Crayfish as Revealed by Three-Dimensional Morphometry

Abstract We have quantitatively analyzed the three-dimensional dendritic structure of an identified nonspiking interneuron, Local Directionally Selective (LDS) interneuron in the terminal abdominal ganglion of the crayfish, Procambarus clarkii Girard, using a confocal laser scanning microscopic system. Comparison of the cell size before and after fixation followed by dehydration and clearing revealed that the diameter of dendritic branches shrank by about 15% while the branch length showed no significant change. The soma and dendritic diameter in vivo were obtained from the measurement in the cleared preparation multiplied by the shrinkage factor. The total length of dendrites and their membrane area as well as their electrotonic structure were found to vary from preparation to preparation. The spatial distribution of fine dendritic branches was variable, but that of major branches was constant among preparations. The interneuron further shared bilaterally asymmetrical dendritic structure: those branches ...