Bulk Nanoscale Research Articles

Microemulsions As Emerging Electrolytes: The Correlation of Structure to Electrochemical Response

Microemulsions are a breakthrough electrolyte for energy storage (BEES) that is emerging as an alternative to traditional RFB electrolytes because of their ability to produce thermodynamically stable, homogeneous solutions of polar and non-polar molecules. The stabilization of oil and water solutions allows microemulsion electrolytes to accommodate organic redox species with fast electron transfer rates that are not soluble in the aqueous phase while still offering the high conductivity of an aqueous salt electrolyte. Microemulsion electrolytes consist of two immiscible phases stabilized by a surfactant, a non-polar phase, solubilizing the redox material—or the redox material can be the entire oil phase—and an aqueous brine phase. Moreover, each component can be environmentally and biologically safe. For example, the aqueous phase only consists of salt and water, the surfactant used in this study, polysorbate-20, is found in many cosmetics and food products, and some of the redox materials investigated in our lab are vitamins such as menadione (vitamin K3) and tocopherol (vitamin E).Microemulsions form many self-assembled bulk nanoscale structures, such as oil-in-water or water-in-oil droplets and bicontinuous. Furthermore, microemulsions exhibit ordering near surfaces that can be different from the bulk structure. Understanding the bulk and surface structures is critical to understanding a material's properties, such as conductivity and diffusion to an electrode surface. Understanding structural changes with composition variation and surface hydrophobicity provide a path to optimizing the balance between acceptable conductivity levels in the electrolyte and the high volume of an oil phase bearing the redox-active species in a µE. This optimization is critical to achieving high-performing electrochemical systems using µEs.This talk describes structural studies of microemulsions prepared from water, toluene, butanol, and polysorbate-20. Small-angle neutron scattering was used to monitor the development of the bicontinuous system as a function of the water-to-surfactant mass ratio on a constant oil-to-surfactant dilution line, revealing how the domain size, correlation length, amphiphilicity factor, and bending moduli change with composition. Kratky and Porod analyses are also employed, providing further structural detail of the scattering domains. We demonstrate that controlling the water-to-surfactant ratio with a constant oil-to-surfactant dilution affects the bicontinuous phase, reveals a sizeable compositional region with structural similarities, and provides insight into the correlation of structure to physical properties. Additionally, neutron reflectivity was used to probe the surface ordering of the microemulsions with hydrophilic and amphiphilic surfaces. Figure 1

Enhanced thermal coarsening resistance in a nanostructured aluminum-cerium alloy produced by additive manufacturing

Decreasing microstructural length scales to the nanoscale is a proven way of increasing strength, but the intrinsic metastability of such structures typically makes them susceptible to thermally activated coarsening. Recent advances in additive manufacturing permit bulk-nanostructured materials to be produced through rapid solidification, but like other metastable materials the as-built structures typically coarsen rapidly with even modest thermal exposure. Here, selective laser melting is employed to produce an Al-Ce-based alloy with high mechanical strength arising from the as-built microstructure, which can be controlled by build conditions. In addition, the alloy exhibits extreme resistance to thermal coarsening up to 400 °C and superior strength retention compared to conventional Al alloys after extended thermal exposure. The near-zero solubility of Ce in Al and potent solid solution strengthening of Mg enable this behavior without requiring heat treatment. This result demonstrates that combining insoluble alloying elements with additive manufacturing is a viable method of producing exceptionally stable bulk nanoscale alloys.

Effects of plasma on the formation of bulk nanoscale structures with lateral dimensions on the surface of GaAs

In this work, the effect of plasma on the formation of bulk nanoscale structures with lateral dimensions on the GaAs surface was studied. The relative change in the area of the bulk structures in different crystallographic directions is demonstrated, in comparing the before and after the operations of modification and profiling with a successive change in the etching time from 0.5 to 2 minutes. The obtained data in the course of the study showed that when applying this technology for producing nanoscale structures, it is necessary to take into account a number of parameters, such as the crystallographic direction of the substrate, the etching time, and the formation voltage of oxide nanostructures.

Nanobubbles from Ethanol‐Water Mixtures: Generation and Solute Effects via Solvent Replacement Method

AbstractReplacement of ethanol‐water solutions (70 – 100% v/v) with deionized water was performed in a flow cell of a particle size analyzer. The resulting alcohol solutions were found to contain bulk nanoscale bubbles due to air supersaturation as can be induced by the difference in gas solubility of the solvents. The effect of charged and polar solutes (salt and sugar) that may influence the formation and surface chemistry of nanobubbles was also determined. Dispersion characteristics such as hydrodynamic diameter, particle concentration, along with the particle‘s electrokinetic property were measured all at once using light scattering techniques after solution replacement with and without the solute species. Light scattering results showed that the resulting solutions upon exchange have higher particle quantities than the starting ethanol‐water solvents with smaller diameters ranging from 80 to 160 nm due to nanobubble formation. The claim for air supersaturation forming nanobubbles that may have resulted to the increase in particle density can also be deduced from the obtained optical images in a microscope. The electrokinetic potential or zeta potential was also higher for the solvent exchange protocols entailing for a selective orientation of ethanol molecules in a bubble surface. More importantly, In terms of solute effects, it appears that while salt anions promote gaseous diffusion, sugar molecules inhibit it.

Synthesis of uniform bulk nanoporous palladium with tunable structure

This work presents systematic investigations on the synthesis of hierarchical nanoporous Pd via electrochemical dealloying of CuPd alloys in sulfuric acid. The impact of electrode potential, dealloying temperature, and additional annealing on microstructure and morphology is explored. Dealloying Cu85Pd15 in 1M sulfuric acid at elevated temperature provides a facile strategy to produce bulk nanoporous Pd samples which are uniform, hierarchically nanoporous, and free of macro-scale cracks. The question “Why will one-step template-free dealloying yield a hierarchical and not unimodal nanoporous structure?” is discussed. The impact of passivation and of a percolating Cu-rich cluster on the pore structure is inspected. A structural instability concept for dealloying of dilute master alloys is preferred as the underlying mechanism. Nanoporous Pd with classical, unimodal pore structure and tunable ligament size ranging from 80 to 270 nm emerges when the as-prepared hierarchical nanoporous Pd is annealed. The material of this study may provide a model system that complements nanoporous Au for studies of bulk nanoscale metal networks as functional and structural materials.

Nanostructural Investigation of Case Hardened Steels for Speed Gears Applications by Small-Angle Neutron Scattering (SANS)

17NiCrMo7, 19MnCr5 and 27MnCr5 low-alloy case-hardening steels samples have been investigated by SANS (Small-Angle Neutron Scattering), to achieve data on bulk nanoscale structure characterisation and complementary analytical and crystallographic information. The reported results are related in particular to the size distribution of nanosized pores which can help to comprehend the structural basis for the physico-chemical properties and thus to improve quality and durability of the considered materials. A complementary PIXE investigation has been also carried out, with the aim of a non-destructive assessment of the elemental composition of the considered samples.

Metal–phenanthroline fused Ti17 clusters, a single molecular source for sensitized photoconductive films

Much attention has been paid to titanium oxo clusters (TOCs) because of their use as model compounds of bulk nanoscale titanium oxides. On the other hand, doping of TiO2 with some metal complexes of 1,10-phenanthroline (phen) or bipyridine (bpy) results in low band-gap materials with high photovoltaic conversion efficiency. In this work, two metal–phenanthroline substituted titanium-oxo-clusters, [Ti17O28(OiPr)16(CoIIphen)2] (C1) and [Ti17O28(OiPr)18(CdIIphen)2] (C2), were successfully prepared by one-step in situ solvothermal synthesis. The structures of the compounds are best described as an oxo-isopropanoxo Ti17 parent fused with two M–phen moieties. They are the first examples of M–phen modified oxo-alkoxy titanium clusters. The band structure of the cluster is modified by the coordination of the metal complex and the absorption of the material is improved. The cluster can not only be used as a model for theoretical study, but can also be used as a precursor to prepare sensitized TiO films. Films (F1) with unique microstructures of hollow spheres, bowls, and doughnuts were obtained by a simple non-template coating method from the solution of Co–phen–TiO cluster C1. The size of the spheres is about 1–2 μm and the thickness of the shell is about 50 nm. Upon repetitive irradiation of the F1 film on the ITO electrode in a three electrode system, a clear photocurrent response was observed. The Co–phen moiety plays an important role in electron transition.

Molecular engineering of nanoscale order in organic electro-optic glasses

The rational design of bulk nanoscale order in organic electro-optic materials, where the strong dipole–dipole interactions tend to dominate over the weaker forces exploited for self-assembly processes, remains an attractive yet elusive goal. Towards this end, a series of pseudo-discotic dipolar nonlinear optical chromophores have been synthesized and fully characterized. Theoretical guidance and an iterative molecular design process have succeeded in engineering long-range nanoscale order in organic electro-optic glasses. Small-angle thin-film X-ray diffraction experiments demonstrate a self-assembled lamellar morphology in a majority of these materials. Cryogenic crystallography, using a synchrotron X-ray source, afforded the structure of a representative system. This structure, in concert with thin-film X-ray diffraction, atomic force microscopy, UV-vis-NIR absorption spectroscopy, and refractive index experiments elucidated the nanoscale order in the films. Application of these materials in electro-optics is discussed.

New Developments in the Processing of Bulk Nanoscale Metals Using High-Pressure Torsion

High-pressure torsion is a processing technique involving the application of a high pressure with concurrent torsional straining. Excellent grain refinement may be achieved using this process with the average grain size often reduced to the nanoscale range. Although this processing is expected to lead to significant microstructural inhomogeneity, experiments consistently demonstrate a gradual evolution towards a homogeneous structure. Recent results have also revealed unusual flow patterns in HPT processing including grain agglomeration in a two-phase alloy and the development of double-swirls and vortices in a stainless steel.

Bulk nanoscale materials in steel products

Although a number of nanoscale metallic materials exhibit interesting mechanical properties the fabrication paths are often complex and difficult to apply to bulk structural materials. However a number of steels which exhibit combinations of plasticity and phase transitions can be deformed to produce ultra high strength levels in the range 1 to 3 GPa. The resultant high stored energy and complex microstructures allow new nanoscale structures to be produced by combinations of recovery and recrystallisation.The resultant structures exhibit totally new combinations of strength and ductility to be achieved. In specific cases this also enables both the nature of the grain boundary structure and the spatial variation in structure to be controlled. In this presentation both the detailed microstructural features and their relation to the strength, work-hardening capacity and ductility will be discussed for a number of martensitic and austenitic steels.

Long-Range Ordering: An Approach to Synthesize Nanoscale Ni-Mo-Based Superlattices with High Strength and High Ductility

It is shown that long-range ordering in certain alloys based upon the Ni-Mo system can provide a viable means for synthesizing bulk nanoscale materials combing high strength and high ductility. Three alloys were included in the study with nominal chemical compositions of Ni-27Mo, Ni-27Mo-0.03B, and Ni-27Mo-12Cr all in weight %. Ordering was induced by thermal aging at 700 oC resulting in a D1a superlattice (Ni4Mo) in the Ni-27Mo and Ni-27Mo-0.03B alloys, and a Pt2Mo-type superlattice [Ni2(Cr,Mo)] in the Ni-27Mo-12Cr alloy. During the early stages of aging, atomic order in the Ni-27Mo alloy was completed homogeneously in the matrix resulting in a nanoscale superlattice with high strength and high ductility, however, a considerable loss of ductility occurred after extended aging. The results suggested that this behavior was not related to the degree of atomic order but rather to a change in morphology resulting from a heterogeneous ordering reaction at grain boundaries promoted by strain-induced recrystallization. Although a nanoscale superlattice combining high strength and high ductility could be synthesized in the Ni-27Mo alloy by proper aging treatment, it is demonstrated that the heterogeneous ordering reaction could be suppressed by the addition of boron or chromium to improve the thermal stability of the alloy system. On the average, a combination of about 800 MPa yield strength and 40% tensile elongation at room temperature could be achieved in the alloys studied. Deformation in the ordered state is found to occur by twinning, which has been related to the crystallography of the disorder-order transformation.

Origin of Bulk Nanoscale Morphology in Conducting Polymers

Origin of Bulk Nanoscale Morphology in Conducting Polymers

Engineered Macroporosity in Single-Wall Carbon Nanotube Films

A key advantage of bulk nanoscale materials in applications ranging from energy storage to chemical catalysis is their inherent high surface area. Single-wall carbon nanotube films possess the additional advantages of high electrical conductivity and robust mechanical integrity. Nevertheless the flexibility of the individual nanotubes and their affinity for each other conspire to obstruct the porosity in such films limiting the perfusion rate of liquids and gases, restricting the accessible surface area and thereby limiting their utility in important applications. Here we demonstrate a simple, effective means to engineer controlled porosity into the nanotube films. The newly incorporated porosity modifies the film electrolytic capacitance and comparative perfusion rates. Pseudocapacitive RuO(2) electrodeposited onto the highest porosity films exhibits a specific capacitance of 1084 F/g. Knowledge of the underlying nanotube capacitance and mass permits extraction of the deposited RuO(2) specific capacitance of 1715 F/g, which closely approaches the predicted theoretical maximum RuO(2) capacitance of 2000 F/g.

Application of long-range ordering in the synthesis of a nanoscale Ni 2 (Cr,Mo) superlattice with high strength and high ductility

We demonstrate that bulk nanoscale materials with high strength and high ductility can be synthesized by using long-range ordering in certain alloy systems. In the case of a Ni-18.6 atomic % Mo-15.1 atomic % Cr, a bulk nanoscale superlattice of Ni 2(Cr,Mo) isomorphous with Pt 2Mo has been synthesized by thermal aging at 700 °C. The superlattice is shown to have high strength and high ductility as well as high thermal stability. Although the yield strength is nearly doubled in the ordered state exceeding 800 MPa, the material is found to maintain about 70% of its initial tensile ductility corresponding to 42% engineering strain. This behavior has been related to the crystallography of the ordering transformation. Although most of the slip systems of the parent face-centered cubic lattice are suppressed by ordering, most of the twinning systems remain energetically favorable. Therefore, deformation in the ordered state is found to predominantly occur by twinning rather than by slip giving rise to the observed combination of high strength and high ductility.

Mechanical properties of Zr-based bulk glassy alloys containing nanoscale compound particles

For the last decade, bulk glassy alloys have been developed in a number of multicomponent alloy systems and have already gained practical applications. Although the bulk glassy alloys in Zr-based systems have high strength and good toughness, it has been found that the addition of special elements to the Zr-based glassy alloys causes the formation of a nanoscale mixed structure consisting of nanoscale intermetallic particles embedded in a glassy matrix and the mixed phase alloys exhibit higher mechanical strength and larger elongation as compared with the corresponding glassy single phase alloys. In particular, the bulk nanoscale mixed phase alloys in the Zr–Al–Ni–Cu–Nb system produced by squeeze casting exhibit extremely high bending flexural strength of 4400 MPa without fracture during the three point bending test. The mechanism for the formation of the nanoscale mixed structure for the alloys containing special additional elements as well as the reason for the remarkable improvement in the mechanical properties has been discussed on the basis of experimental results obtained by high-resolution TEM, nanobeam EDX spectroscopy, atom probe FIM and small angle X-ray scattering, in addition to DSC, ordinary TEM and X-ray diffraction.

金属粉末を繰り返し圧縮・圧延することにより作製したＦｅ／Ａｇナノスケール人工格子の磁気抵抗効果の評価

Starting from the mixture of elemental powder mixtures, we produced bulk nanoscale Fe/Ag multilayers by the repeated press-rolling method. The average thikness of this sample was 5nm for Fe and 8nm for Ag. This sample exhibited the CIP-MR of 8.5 % at 77 K.