Nanocrystalline Domains Research Articles

Spider prey-wrapping silk is an α-helical coiled-coil/β-sheet hybrid nanofiber.

Solid-State NMR results on 13C-Ala/Ser and 13C-Val enriched Argiope argentata prey-wrapping silk show that native, freshly spun aciniform silk nanofibers are dominated by α-helical (∼50% total) and random-coil (∼35% total) secondary structures, with minor β-sheet nanocrystalline domains (∼15% total). This is the most in-depth study to date characterizing the protein structural conformation of the toughest natural biopolymer: aciniform prey-wrapping silks.

Distinguishing Surface versus Bulk Hydroxyl Groups of Cellulose Nanocrystals Using Vibrational Sum Frequency Generation Spectroscopy.

In plant cell walls and cellulose-containing composites, nanocrystalline cellulose interacts with water molecules or matrix polymers through hydrogen bonding of the hydroxyl groups at the cellulose surface. These interactions play key roles in cellulose assembly in plant cell walls and mechanical properties of cellulose composites; however, they could not be studied properly due to the spectroscopic difficulty of selectively detecting the surface hydroxyl groups of nanocrystalline domains. This study employed the sum frequency scattering principle to distinguish the hydroxyl groups inside of the crystalline nanodomain of cellulose and those exposed at the surface of crystalline domains. The comparison of the spectra at various scattering angles revealed that the OH peak near ∼3450 cm-1 comes from the weakly hydrogen-bonded OH groups at the surface of crystalline cellulose. Also, a time delay measurement found that the sharp vibrational features observed near 3700 cm-1 can be attributed to isolated OH groups not accessible by ambient water molecules. These findings allow the distinction of surface versus bulk OH groups in sum frequency generation vibrational spectroscopy.

Triple-shelled ZnO/ZnFe2O4 heterojunctional hollow microspheres derived from Prussian Blue analogue as high-performance acetone sensors

Semiconductor oxides with hierarchically hollow architecture can provide significant advantages as sensing materials for gas sensing by facilitating the diffusion of target gases and the surface reaction. A cost-efficient and facile strategy is developed to scalably fabricate triple-shelled hollow binary ZnO/ZnFe2O4 (ZZFO) metal oxides microspheres with excellent intimate heterojunctions through a morphology-inherited annealing treatment of single-resource Prussian Blue analogue of Zn3[Fe(CN)6]2·xH2O solid microspheres as self-sacrificial templates. The porous hybrid ZZFO triple-shelled hollow microspheres (TSHMSs) are demonstrated to be composed of crystalline ZnO and ZnFe2O4 nano-domains with well homogeneous dispersion at the nanoscale and large void spaces between adjacent shells. When evaluated as sensors towards acetone vapor, benefiting from the striking synergy and interplay between active bicomponents and the intrinsic structural advantages, the as-fabricated ZZFO TSHMSs sensor exhibited high performances, including excellent sensitivity, good selectivity and high reversibility, rapid response ability at ultralow working temperature (140°C). Of great significance, these prominent findings may pave the way towards optimizational design and efficient fabrication of mixed metal oxides derived from other PBAs or even other MOFs as high-performance gas sensors in the future.

Processing nanoparticle\u2013nanocarbon composites as binder-free electrodes for lithium-based batteries

The processing of battery materials into functional electrodes traditionally requires the preparation of slurries using binders, organic solvents, and additives, all of which present economic and environmental challenges. These are amplified in the production of nanostructured carbon electrodes which are often more difficult to disperse in slurries and require more energy-intensive and longer processing. In this study we demonstrate a new process for preparing binder-free nanocarbon/nanoparticle (Fe–C) composite electrodes and study the effect of processing on the nanocomposite’s cycling performance in lithium cells. The binder-free electrodes were prepared by a two-step method: pulsed-electrodeposition of iron-based catalyst followed by chemical vapor deposition of a carbon film. SEM and TEM of the Fe–C showed that the active materials have a fibrous and tortuous morphology with disordered nanocrystalline domains characteristic of an amorphous carbon. The Fe–C electrodes showed good mechanical stability and an excellent cycle performance with an average stable capacity of 221 mAhg−1, and 85% capacity retention for up to 50 cycles. By reducing the number of processing steps and eliminating the use of binders and other chemicals this new method offers a “greener” alternative than current processing methods.Graphical abstractSynopsis: gains in sustainability can be achieved by eliminating use of binders, chemicals, and the number of electrode’s processing steps in this new method.

Lignin-based carbon fibers for renewable and multifunctional lithium-ion battery electrodes

Abstract Lignin-based carbon fibers (LCFs) from the renewable resource softwood kraft lignin were synthesized via oxidative thermostabilization of pure melt-spun lignin and carbonization at different temperatures from 1000°C to 1700°C. The resulting LCFs were characterized by tensile testing, scanning electron microscopy (SEM), X-ray diffraction (XRD) and confocal Raman spectroscopy. The microstructure is mainly amorphous carbon with some nanocrystalline domains. The strength and stiffness are inversely proportional to the carbonization temperature, while the LCFs carbonized at 1000°C exhibit a strength of 628 MPa and a stiffness of 37 GPa. Furthermore, the application potential of LCFs was evaluated as negative electrodes in a lithium-ion battery (LIB) by electrochemical cycling at different current rates in a half-cell setup. The capacity drops with the carbonization temperature and the LCFs carbonized at 1000°C have a capacity of 335 mAh g−1. All LCFs showed good cycling stability. Because of the mechanical integrity and conductivity of the LCFs, there is no need to apply current collectors, conductive additives or binders. The advantage is an increased gravimetric energy density compared to graphite, which is the most common negative electrode material. LCFs show a promising multifunctional behavior, including good mechanical integrity, conductivity and an ability to intercalate lithium for LIBs.

Mesoscale martensitic transformation in single crystals of topological defects

Liquid-crystal blue phases (BPs) are highly ordered at two levels. Molecules exhibit orientational order at nanometer length scales, while chirality leads to ordered arrays of double-twisted cylinders over micrometer scales. Past studies of polycrystalline BPs were challenged by the existence of grain boundaries between randomly oriented crystalline nanodomains. Here, the nucleation of BPs is controlled with precision by relying on chemically nanopatterned surfaces, leading to macroscopic single-crystal BP specimens where the dynamics of mesocrystal formation can be directly observed. Theory and experiments show that transitions between two BPs having a different network structure proceed through local reorganization of the crystalline array, without diffusion of the double-twisted cylinders. In solid crystals, martensitic transformations between crystal structures involve the concerted motion of a few atoms, without diffusion. The transformation between BPs, where crystal features arise in the submicron regime, is found to be martensitic in nature when one considers the collective behavior of the double-twist cylinders. Single-crystal BPs are shown to offer fertile grounds for the study of directed crystal nucleation and the controlled growth of soft matter.

Combustion synthesis, structural and magnetic characterization of Ce1−xPrxO2 system

The current work describes the synthesis of Ce1−xPrxO2 (x = 0.0, 0.2, 0.4, 0.6, 0.8) and Pr6O11 systems by the combustion method, using citric acid as chelating agent. The obtained solids after combustion and calcination processes were characterized by thermal analysis (TGA-DTA) and infrared spectroscopy (FT-IR) to evaluate the chemical process during the combustion reaction. The surface area analysis using isotherms of nitrogen adsorption, reveal that all samples exhibit values between 70 and 135 m2 g−1, with a pore volume that allows its classification as mesoporous materials. The structural analysis by X-ray diffraction (XRD) and Rietveld refinement, revealed the obtention of a pure cubic structure Fm3m (225) along all cerium oxide modifications with nanocrystalline domain sizes, except for the praseodymium oxide that shows two crystalline phases in a monoclinic crystalline phase P12 1 /c 1 (14) in the case of Pr6O11 and a cubic phase Fm3m (225) for PrO2 oxide. The oxygen storage capacity measurements performed in all samples, demonstrate that exchange of Ce ions by Pr increases the storage capacity of samples over the reference values in accordance with the synthesis method. The characterization by high-resolution transmission electron microscopy, confirmed that the solids are composed by nanometric aggregates with d spacing between 0.29 and 0.31 nm along main diffraction signals, in accordance with the experimental XRD results. Finally, the magnetic characterization in a ZFC configuration and a M-H mode, shows a strong paramagnetic behavior in all systems except in CeO2 oxide, which exhibited a prevalent diamagnetic behavior.

Study on the microstructural evolution of Ti-Nb based alloy obtained by high-energy ball milling

Titanium-based alloys are widely used in biomedical applications because of their good properties such as fatigue resistance, workability, corrosion resistance and biocompatibility. The effect of milling time on the deformation-driven alloying mechanisms in the system Ti-30Nb-13Ta-2Mn (wt.%) during mechanical alloying (MA) has been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). High-energy milling was performed in controlled atmosphere of argon at different times (1, 5, 10, 20, 30, 50, 70, 90 and 110 h), using agate as grinding media. The XRD-patterns showed the formation of Ti-β solid solution occurred above 20 h of milling. Due to the high energy of this process, the formation of Ti-β and Nb-fcc crystalline phases embedded in an amorphous phase was promoted. The longer alloying time above 50 h resulted in spherical morphology and texturing of the synthetized alloy which were evidenced from the SEM and XRD analyses, respectively. Lattice parameters, mean crystallite size and microstrain (root mean square, rms) were obtained from Rietveld analysis using MAUD software. The nanocrystalline domains were also quantified by TEM, which showed the coexistence of amorphous and nanocrystalline particles of Mn2Ti, MnTi, NbTi4, Nb-fcc and Ti-β embedded in an amorphous phase.

Spin Probe Multi-Frequency EPR Study of Unprocessed Cotton Fibers.

Known since the ancient times, cotton continues to be one of the essential materials for the human civilization. Cotton fibers are almost pure cellulose and contain both crystalline and amorphous nanodomains with different physicochemical properties. While understanding of interactions between the individual cellulose chains within the crystalline phase is important from a perspective of mechanical properties, studies of the amorphous phase lead to characterization of the essential transport parameters, such as solvent diffusion, dyeing, drug release, and toxin absorption, as well as more complex processes of enzymatic degradation. Here, we describe the use of spin probe electron paramagnetic resonance methods to study local polarity and heterogeneous viscosity of two types of unprocessed cotton fibers, G. hirsutum and G. barbadense, harvested in the State of North Carolina, USA. These fibers were loaded with two small molecule nitroxide probes that differ in polarity-Tempo and its more hydrophilic derivative Tempol-using a series of polar and non-polar solvents. The electron paramagnetic resonance spectra of the nitroxide-loaded cotton fibers were analyzed both semi-empirically and by least-squares simulations using a rigorous stochastic theory of electron paramagnetic resonance spectra developed by Freed and coworkers. A software package and least-squares fitting protocols were developed to carry out automatic simulations of multi-component electron paramagnetic resonance spectra in both first-derivative and the absorption forms at multiple resonance frequencies such as X-band (9.5 GHz) and W-band (94.3 GHz). The results are compared with the preceding electron paramagnetic resonance spin probe studies of a commercial bleached cotton sheeting carried out by Batchelor and coworkers. One of the results of this study is a demonstration of a co-existence of cellulose nanodomains with different physicochemical properties such as polarity and microviscosity that are affected by solvents and temperature. Spin labeling studies also revealed a macroscopic heterogeneity in the domain distribution along the cotton fibers and a critical role the cuticular layer is playing as a barrier for spin probe penetration. Finally but not lastly, the simultaneous multi-component least-squares simulation method of electron paramagnetic resonance spectra acquired at different resonant frequencies and the display forms (e.g., absorption and first-derivative displays) and the strategy of spectral parameter sharing could be potentially applicable to other heterogeneous biological systems in addition to the cotton fibers studies here.

Structural Investigations of Supercontracted Spider Dragline Silk

Spider dragline silk is a semicrystalline polymer of great interest in materials science due to its unique mechanical properties and biocompatibility. Spun from the major ampullate glands, this type of silk possesses an exceptional combination of elasticity, strength and toughness. At the molecular level, spider silk is composed of fibrous proteins organized into crystalline nanodomains embedded in an amorphous matrix. In the presence of liquid water or high humidity, the amorphous phase is plasticized and its hydrogen bonding network disrupted, which results in the shrinking of the fiber up to 50% of its initial length. This phenomenon, known as supercontraction, is triggered by the entropic folding of the polypeptide chains resulting from the water-induced increase in chain mobility. However, disagreements exist in the literature as to whether a change in the secondary structure of the protein occurs or not during supercontraction. Furthermore, although it has already been established that supercontraction induces a disorientation of the molecular units, this effect has not been quantified yet. Therefore, we will investigate and quantify, for different species, the conformational and orientational variations of the silk proteins induced by supercontraction. To achieve our goals, we will use Raman spectromicroscopy, a technique that as long been proven to be a useful tool to probe silk. Moreover, the effects of drawing speed on the magnitude of supercontraction will also be examined.

Bottom-up engineering of thermoelectric nanomaterials and devices from solution-processed nanoparticle building blocks.

The conversion of thermal energy to electricity and vice versa by means of solid state thermoelectric devices is extremely appealing. However, its cost-effectiveness is seriously hampered by the relatively high production cost and low efficiency of current thermoelectric materials and devices. To overcome present challenges and enable a successful deployment of thermoelectric systems in their wide application range, materials with significantly improved performance need to be developed. Nanostructuration can help in several ways to reach the very particular group of properties required to achieve high thermoelectric performances. Nanodomains inserted within a crystalline matrix can provide large charge carrier concentrations without strongly influencing their mobility, thus allowing to reach very high electrical conductivities. Nanostructured materials contain numerous grain boundaries that efficiently scatter mid- and long-wavelength phonons thus reducing the thermal conductivity. Furthermore, nanocrystalline domains can enhance the Seebeck coefficient by modifying the density of states and/or providing type- and energy-dependent charge carrier scattering. All these advantages can only be reached when engineering a complex type of material, nanocomposites, with exquisite control over structural and chemical parameters at multiple length scales. Since current conventional nanomaterial production technologies lack such level of control, alternative strategies need to be developed and adjusted to the specifics of the field. A particularly suitable approach to produce nanocomposites with unique level of control over their structural and compositional parameters is their bottom-up engineering from solution-processed nanoparticles. In this work, we review the state-of-the-art of this technology applied to the thermoelectric field, including the synthesis of nanoparticles of suitable materials with precisely engineered composition and surface chemistry, their combination and consolidation into nanostructured materials, the strategies to electronically dope such materials and the attempts to fabricate thermoelectric devices using nanoparticle-based nanopowders and inks.

Understanding the graphitization and growth of free-standing nanocrystalline graphene using in situ transmission electron microscopy.

Graphitization of polymers is an effective way to synthesize nanocrystalline graphene on different substrates with tunable shape, thickness and properties. The catalyst free synthesis results in crystallite sizes on the order of a few nanometers, significantly smaller than commonly prepared polycrystalline graphene. Even though this method provides the flexibility of graphitizing polymer films on different substrates, substrate free graphitization of freestanding polymer layers has not been studied yet. We report for the first time the thermally induced graphitization and domain growth of free-standing nanocrystalline graphene thin films using in situ TEM techniques. High resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS) techniques were used to analyze the graphitization and the evolution of nanocrystalline domains at different temperatures by characterizing the crystallinity and domain size, further supported by ex situ Raman spectroscopy. The graphitization was comparable to the substrate supported heating and the temperature dependence of graphitization was analyzed. In addition, the in situ analysis of the graphitization enabled direct imaging of some of the growth processes taking place at different temperatures.

Nanoscale Structural Features in Major Ampullate Spider Silk.

Spider major ampullate silk is often schematically represented as a two-phase material composed of crystalline nanodomains in an amorphous matrix. Here we are interested in revealing its more complex nanoscale organization by probing Argiope bruennichi dragline-type fibers using scanning X-ray nanodiffraction. This allows resolving transversal structural features such as an about 1 μm skin layer composed of around 100 nm diameter nanofibrils serving presumably as an elastic sheath. The core consists of a composite of several nm size crystalline nanodomains with poly(l-alanine) microstructure, embedded in a polypeptide network with short-range order. Stacks of nanodomains separated by less ordered nanosegments form nanofibrils with a periodic axial density modulation which is particularly sensitive to radiation damage. The precipitation of larger β-type nanocrystallites in the outer core-shell is attributed to MaSp1 protein molecules.

Metal ion-induced H-aggregation of a water-soluble anionic dye Congo red (CR) in Langmuir–Blodgett (LB) film

Present communication reports the preparation of Langmuir monolayer of water-soluble anionic dye Congo red (CR) by allowing it to adsorb from the aqueous subphase onto the preformed Langmuir monolayer of anionic stearic acid using divalent metal cations Mg2+ as mediator. Isotherm and compressibility studies of SA-Mg-CR hybrid monolayer gave valuable information about the molecular organisation in the Langmuir monolayer. Absorption spectroscopic studies revealed the formation of H-aggregates in the hybrid Langmuir–Blodgett (LB) films fabricated at lower salt concentration in the subphase. Atomic Force Microscopic image gave visual evidence of distinct nanocrystalline domains in the LB monolayer film.

Phase Restructuring in Transition Metal Dichalcogenides for Highly Stable Energy Storage.

Achieving homogeneous phase transition and uniform charge distribution is essential for good cycle stability and high capacity when phase conversion materials are used as electrodes. Herein, we show that chemical lithiation of bulk 2H-MoS2 distorts its crystalline domains in three primary directions to produce mosaic-like 1T' nanocrystalline domains, which improve phase and charge uniformity during subsequent electrochemical phase conversion. 1T'-LixMoS2, a macroscopic dense material with interconnected nanoscale grains, shows excellent cycle stability and rate capability in a lithium rechargeable battery compared to bulk or exfoliated-restacked MoS2. Transmission electron microscopy studies reveal that the interconnected MoS2 nanocrystals created during the phase change process are reformable even after multiple cycles of galvanostatic charging/discharging, which allows them to play important roles in the long term cycling performance of the chemically intercalated TMD materials. These studies shed light on how bulk TMDs can be processed into quasi-2D nanophase material for stable energy storage.

Effect of degree of crystallinity on elastic properties of silicon carbide fabricated using polymer pyrolysis

In this study, silicon carbide (SiC) is fabricated using polymer infiltration and pyrolysis (PIP). Allylhydridopolycarbosilane (AHPCS) is used as the preceramic polymer. Final processing temperatures are varied to observe the change in microstructure as well as physical and mechanical properties. Density, porosity and thermal conductivity are determined as a function of processing temperatures. Microstructural characterization, done using atomic force microscopy (AFM) and X-ray diffraction (XRD), has revealed the presence of nanocrystalline domains with grain sizes in the range of 5–20nm. The degree of crystallinity is determined using non-contact mode atomic force microscopy. The degree of crystallinity follows an increasing trend with processing temperature. Hardness and modulus are determined using nanoindentation, and are found to be influenced by the degree of crystallinity.

Synchrotron high energy X-ray diffraction study of microstructure evolution of severely cold drawn NiTi wire during annealing

Microstructure evolution of a cold-drawn NiTi shape memory alloy wire was investigated by means of in-situ synchrotron high-energy X-ray diffraction during continuous heating. The cold-drawn wire contained amorphous regions and nano-crystalline domains in its microstructure. Pair distribution function analysis revealed that the amorphous regions underwent structural relaxation via atomic rearrangement when heated above 100 °C. The nano-crystalline domains were found to exhibit a strong cold work induced lattice strain anisotropy along 〈111〉, which coincides with the crystallographic fiber orientation of the domains along the wire axial direction. The lattice strain anisotropy systematically decreased upon heating above 200 °C, implying a structural recovery. Crystallization of the amorphous phase led to a broadening of the angular distribution of 〈111〉 preferential orientations of grains along the axial direction as relative to the original 〈111〉 axial fiber texture of the nanocrystalline domains produced by the severe cold wire drawing deformation.

Nanosized Mn-Ni oxide thin films via anodic electrodeposition: a study of the correlations between morphology, structure and capacitive behaviour

The present study addresses the synthesis of manganese-nickel oxide thin films via potentiodynamic anodic electrodeposition as supercapacitor electrodes. We study in particular the effect of the deposition scan rate and of the Ni(II) to Mn(II) molar ratio in the deposition bath on the capacitive behaviour of mixed oxide electrodes. The increase of the nickel content in oxide thin films of composition NixMn1-xOy (with x in the range from 0 to 0.17) results in the increase of specific capacitance up to a maximum for about 10 at% Ni. The deposition scan rate affects the capacitive behaviour of mixed oxide electrodes through its effects on layer morphology and surface structure. In particular, thin film electrodes at about 10 at% Ni show a maximum in the specific capacitance for deposition scan rate of 600mVs−1, which is shown to be related to the attendant modifications in surface morphology and topography. After annealing at 200°C, 6h, partial crystallization of the amorphous structure of the as-grown mixed oxide takes place with formation of dispersed nanocrystalline domains. The annealed electrode at 10 at% Ni, with mass loading of 0.30mgcm−2, show the highest specific capacitance (250Fg−1, at 0.1Ag−1), and specific energy and power as high as 34.5Whkg−1 (at 50Wkg−1), and 4.3kWkg−1 (at 15.7Whkg−1). Mixed oxide of the same composition and mass loading reveal a 122% capacitance retention after 10,000 cycles in 1M Na2SO4 at 20Ag−1.

Soft surfaces of nanomaterials enable strong phonon interactions.

Phonons and their interactions with other phonons, electrons or photons drive energy gain, loss and transport in materials. Although the phonon density of states has been measured and calculated in bulk crystalline semiconductors, phonons remain poorly understood in nanomaterials, despite the increasing prevalence of bottom-up fabrication of semiconductors from nanomaterials and the integration of nanometre-sized components into devices. Here we quantify the phononic properties of bottom-up fabricated semiconductors as a function of crystallite size using inelastic neutron scattering measurements and ab initio molecular dynamics simulations. We show that, unlike in microcrystalline semiconductors, the phonon modes of semiconductors with nanocrystalline domains exhibit both reduced symmetry and low energy owing to mechanical softness at the surface of those domains. These properties become important when phonons couple to electrons in semiconductor devices. Although it was initially believed that the coupling between electrons and phonons is suppressed in nanocrystalline materials owing to the scarcity of electronic states and their large energy separation, it has since been shown that the electron-phonon coupling is large and allows high energy-dissipation rates exceeding one electronvolt per picosecond (refs 10-13). Despite detailed investigations into the role of phonons in exciton dynamics, leading to a variety of suggestions as to the origins of these fast transition rates and including attempts to numerically calculate them, fundamental questions surrounding electron-phonon interactions in nanomaterials remain unresolved. By combining the microscopic and thermodynamic theories of phonons and our findings on the phononic properties of nanomaterials, we are able to explain and then experimentally confirm the strong electron-phonon coupling and fast multi-phonon transition rates of charge carriers to trap states. This improved understanding of phonon processes permits the rational selection of nanomaterials, their surface treatments, and the design of devices incorporating them.

Easily recoverable titanosilicate zeolite beads with hierarchical porosity: Preparation and application as oxidation catalysts

Titanosilicate zeolite beads with hierarchical porosity and 0.2–0.5mm diameter (HPB-TS-1) have been synthesized from a titanosilicate solution, employing a porous anion-exchange resin as shape- and structure-directing template. The characterization results showed the existence of crystalline TS-1 nanoparticles and of a network of connected large meso/macropores in the interior of the beads. These bead materials are active and selective heterogeneous catalysts for two classes of industrially relevant oxidation reactions: the hydroxylation of phenol and the epoxidation of alkenes. In both cases, a green oxidant such as hydrogen peroxide was utilized. HPB-TS-1 beads displayed high activity in the hydroxylation of phenol, due to their crystalline TS-1 structure with isolated tetrahedral Ti species. In the epoxidation of cyclohexene, HPB-TS-1 gave conversion comparable to that over a benchmark catalyst such as Ti-MCM-41, but more than double yield and selectivity of the target product, cyclohexene oxide. HPB-TS-1 was also active and selective in the epoxidation of other bulky alkenes, i.e., cis-cyclooctene and trans, trans, cis-1,5,9-cyclododecatriene. The catalytic performance of HPB-TS-1 stems from the presence of crystalline TS-1 nanodomains, which are accessible through a network of meso/macropores within the beads. Notably, the bead format of these catalysts causes their spontaneous settling upon cessation of the agitation, thus enabling their straightforward separation from the reaction mixture. The HPB-TS-1 catalysts could be efficiently recycled in the hydroxylation of phenol with aqueous H2O2 via a calcination approach.