Nanoscale Curvature Research Articles

Effect of nano-scale curvature on the intrinsic blood coagulation system.

The intrinsic coagulation activity of silica nanoparticles strongly depends on their surface curvature. Nanoparticles with higher surface curvature do not denature blood coagulation factor XII on its surface, providing a coagulation 'silent' surface, while nanoparticles with lower surface curvature show denaturation and concomitant coagulation.

Review of nanostructured carbon materials for electrochemical capacitor applications: advantages and limitations of activated carbon, carbide‐derived carbon, zeolite‐templated carbon, carbon aerogels, carbon nanotubes, onion‐like carbon, and graphene

Electric double layer capacitors, also called supercapacitors, ultracapacitors, and electrochemical capacitors, are gaining increasing popularity in high power energy storage applications. Novel carbon materials with high surface area, high electrical conductivity, as well as a range of shapes, sizes and pore size distributions are being constantly developed and tested as potential supercapacitor electrodes. This article provides an overview of the electrochemical studies on activated carbon, carbide derived carbon, zeolite‐templated carbon, carbon aerogel, carbon nanotube, onion‐like carbon, and graphene. We discuss the key performance advantages and limitations of various nanostructured carbon materials and provide an overview of the current understanding of the structure–property relationships related to the transport and adsorption of electrolyte ions on their surfaces, specific and volumetric capacitance, self‐discharge, cycle life, electrolyte stability, and others. We discuss the impact of microstructural defects, pore size distribution, pore tortuosity, chemistry and functional groups on the carbon surface, nanoscale curvature, and carbon‐electrolyte interfacial energy. Finally, we review state‐of‐the art commercial large scale applications of supercapacitors, including their use in smart grids and distributed energy storage, hybrid electric and electric vehicles, energy efficient industrial equipment, ships, wind power stations, uninterruptible power supplies, power backup, and consumer devices. WIREs Energy Environ 2014, 3:424–473. doi: 10.1002/wene.102This article is categorized under: Fuel Cells and Hydrogen > Science and Materials Energy Infrastructure > Science and Materials Energy and Development > Science and Materials Energy Research & Innovation > Science and Materials

Single-crystalline hafnium carbide nanowire growth below the eutectic temperature by CVD

Single-crystalline hafnium carbide (HfC) nanowires were synthesized by a Ni-catalyst-assisted chemical vapor deposition (CVD) method at 1025°C below the eutectic temperature (TE). The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM). XRD and EDX results indicate that well stoichiometric HfC nanowires were obtained. SEM and TEM investigations show the HfC nanowires possess typical diameters of ~50nm and lengths of tens of microns. Most of the nanowires are grown along 〈112〉 crystal directions and the cluster/column interfaces at the wire tips parallel to the {011} crystal planes. Although the synthesis temperature of the nanowires is at least 75°C lower than TE, the vapor -liquid -solid growth of the HfC nanowires still occurs probably due to nanoscale size effects and curvature effects. In addition, it is found that the diameters of the synthesized products increase when raising the synthesis temperature.

3D Electron Tomography of Pretreated Biomass Informs Atomic Modeling of Cellulose Microfibrils

Fundamental insights into the macromolecular architecture of plant cell walls will elucidate new structure-property relationships and facilitate optimization of catalytic processes that produce fuels and chemicals from biomass. Here we introduce computational methodology to extract nanoscale geometry of cellulose microfibrils within thermochemically treated biomass directly from electron tomographic data sets. We quantitatively compare the cell wall nanostructure in corn stover following two leading pretreatment strategies: dilute acid with iron sulfate co-catalyst and ammonia fiber expansion (AFEX). Computational analysis of the tomographic data is used to extract mathematical descriptions for longitudinal axes of cellulose microfibrils from which we calculate their nanoscale curvature. These nanostructural measurements are used to inform the construction of atomistic models that exhibit features of cellulose within real, process-relevant biomass. By computational evaluation of these atomic models, we propose relationships between the crystal structure of cellulose Iβ and the nanoscale geometry of cellulose microfibrils.

Polarity Control for Nonthiolated DNA Adsorption onto Gold Nanoparticles

Gold nanoparticles (AuNPs) functionalized with thiolated DNA have enabled many studies in nanoscience. The strong thiol/gold affinity and the nanoscale curvature of AuNPs allow the attached DNA to adapt an upright conformation favorable for hybridization. Recently, it has been shown that nonthiolated DNA can also be attached via DNA base adsorption. Without a thiol label, both ends of the DNA and even internal bases could be adsorbed, decreasing the specificity of subsequent molecular recognition reactions. In this work, we employed a modular sequence design approach to systematically study the effect of DNA sequence on adsorption polarity. A block of poly adenine (poly-A) could be used to achieve a high density of DNA attachment. When the poly-A block length is short (e.g., below 5-7), the loading was independent of the block length, and the conjugate cannot hybridize to its cDNA effectively, suggesting a random attachment controlled by adsorption kinetics. Increasing the block length leads to reduced capacity but improved hybridization, suggesting that more DNA with the desired conformation was adsorbed due to the thermodynamic effects of poly-A binding. The design can be further improved by including capping sequences rich in T or G. Finally, a more general double-stranded DNA approach was described to be suitable for DNA that cannot satisfy the above-mentioned design requirements.

Nanoscale effects of silica particle supports on the formation and properties of TiO2 nanocatalysts

Small TiO2 crystals in the anatase phase are in high demand as photocatalysts. Stable TiO2 crystals in the anatase phase were obtained using a silica nanoparticle as a support. The focus of this study was to investigate the nanoscale effect of the silica support on the formation and properties of small anatase crystals. The experiments were carried out using powder X-ray diffraction, differential thermal analysis, transmission electron microscopy, and energy dispersion spectroscopy. The results showed that the size of the silica support played a crucial role in crystallization of TiO2 and regulation of TiO2 properties, including phase transition, crystal size, thermodynamic property and catalytic activity. A nanoscale curvature model of the spherical silica support was proposed to explain these size effects. Finally, the developed TiO2 catalysts were applied to the oxidation of methanol using a high-throughput photochemical reactor. The size effect of the silica supports on the TiO2 catalytic efficiency was demonstrated using this system.

Using Nanoscale Substrate Curvature to Control the Dimerization of a Surface-Bound Protein

The influence of surface geometry on adsorbed proteins offers new possibilities for controlling quaternary structure by manipulating protein-protein interactions at a surface, with applications that are relevant to protein aggregation, fibrillation, ligand binding, and surface catalysis. To understand the effect of surface curvature on the structure of the surface-bound protein β-lactoglobulin (β-LG), we have used a combination of polystyrene (PS) nanoparticles (NPs) and ultrathin PS films to fabricate chemically pure, hydrophobic surfaces that have nanoscale curvature and are stable in aqueous buffer. We have used single molecule force spectroscopy to measure the detachment contour lengths L(c) for β-LG adsorbed on the highly curved PS surfaces, and we compare these values in situ to those measured for β-LG adsorbed on flat PS surfaces on the same samples. The L(c) distributions measured on all flat PS surfaces show a large monomer peak near 60 nm and a smaller dimer peak at 120 nm. For 190 and 100 nm diameter NPs, which are effectively flat on the scale of the β-LG molecules, there is no measurable difference between the L(c) distributions obtained for the flat and curved surfaces. However, for 60 nm diameter NPs the dimer peak is smaller, and for 25 nm diameter NPs the dimer peak is absent, indicating that the number of surface-bound dimers is significantly reduced by an increase in the curvature of the underlying surface. These results indicate that surface curvature provides a new method of manipulating protein-protein interactions and controlling the quaternary structure of adsorbed proteins.

Folded Graphene Membranes: Mapping Curvature at the Nanoscale

While the unique elastic properties of monolayer graphene have been extensively investigated, less knowledge has been developed so far on folded graphene. Nevertheless, it has been recently suggested that fold-induced curvature (without in-plane strain) could possibly affect the local chemical and electron transport properties of graphene, envisaging a material-by-design approach where tailored membranes are used in enhanced nanoresonators or nanoelectromechanical devices. In this work we propose a novel method combining apparent strain analysis from high-resolution transmission electron microscopy (HREM) images and theoretical modeling based on continuum elasticity theory and tight-binding atomistic simulations to map and measure the nanoscale curvature of graphene folds and wrinkles. If enough contrast and resolution in HREM images are obtained, this method can be successfully applied to provide a complete nanoscale geometrical and physical picture of 3D structure of various wrinkle and fold configurations.

Apparent Inverse Gibbs-Thomson Effect in Dealloyed Nanoporous Nanoparticles

The Gibbs-Thomson effect (the reduction of local chemical potential due to nanoscale curvature) predicts that nanoparticles of radius r dissolve at lower electrochemical potentials than bulk materials, decreasing as 1/r. However, we show here that if the particle is an alloy--susceptible to selective dissolution (dealloying) and nanoporosity evolution--then complete selective electrochemical dissolution and porosity evolution require a higher electrochemical potential than the comparable bulk planar material, increasing empirically as 1/r. This is a kinetic effect, which we demonstrate via kinetic Monte Carlo simulation. Our model shows that in the initial stages of dissolution, the less noble particle component is easily stripped from the nanoparticle surface, but owing to an increased mobility of the more noble atoms, the surface of the particle quickly passivates. At a fixed electrochemical potential, porosity and complete dealloying can only evolve if fluctuations in the surface passivation layer are sufficiently long-lived to allow dissolution from percolating networks of the less-noble component that penetrate through the bulk of the particle.

Water molecule encapsulated in carbon nanotube model systems: effect of confinement and curvature

Water present in the nanoscale confined medium like the hydrophobic interior of the carbon nanotubes (CNT) is known to extol unique properties that depart largely from their behavior in the bulk form. Considering suitable model systems that structurally resemble single unit of the CNT, we demonstrate that two unique parameters namely the local nanoscale curvature and the confinement length are of cardinal importance in governing the structural and electronic properties of water molecule present inside CNT in a general manner. Water molecule encapsulated between the model systems that offer both the above two effects exhibits dramatic trend in the interaction energy with respect to the variation of these parameters. In relation to the curvature of the model system, we propose three different regimes where water molecule experiences a distinct trend in the stabilization energy. Similarly, a confinement distance of 6 A also marks as a borderline for the distinct manifestations in the stabilization energy of the water molecule. These two parameters also play a key role in governing the significant variations in the structural parameters, Mulliken charges, and red and blue shift in the O–H vibrational frequencies of the encapsulated water molecule. There seems to be interplay between curvature and confinement in deciding the electronic properties of water in the nanoscale confinement.

Effect of nanoscale curvature sign and bundle structure on supercritical H2 and CH4 adsorptivity of single wall carbon nanotube

The adsorptivities of supercritical CH4 and H2 of the external and internal tube walls of single wall carbon nanotube (SWCNT) were determined. The internal tube wall of the negative curvature showed the higher adsorptivities for supercritical CH4 and H2 than the external tube wall of the positive curvature due to their interaction potential difference. Fine SWCNT bundles were prepared by the capillary force-aided drying treatment using toluene or methanol in order to produce the interstitial pore spaces having the strongest interaction potential for CH4 or H2; the bundled SWCNT showed the highest adsorptivity for supercritical CH4 and H2. It was clearly shown that these nanostructures of SWCNTs are crucial for supercritical gas adsorptivity.

Controlling the Properties of Self-Assembled Monolayers by Substrate Curvature

Properties of self-assembled monolayers (SAMs) can be tailored by the curvature of the underlying surface. This is so because on a curved support the density of SAM headgroups is always smaller than that of the surface-attachment sites. This density difference increases with increasing curvature and is most pronounced for SAMs formed on nanoscopic particles. This Perspective describes systems in which nanoscale curvature causes pronounced changes in the pK(a) of acid-presenting SAMs or in the electrochemical potential of redox-active molecules (including supramolecular "switches") attached to nanoparticles. It is suggested that in nanoparticles having regions of different curvature these geometrical differences can translate into site-selective charging; such "patchy" particles could be used as building blocks of pH-sensitive assemblies.

Corrugation of the external surface of multiwall carbon nanotubes by catalytic oxidative etching and its effect on their decoration with metal nanoparticles

It was established that partial combustion of carbon constituting the walls of multiwall carbon nanotubes (MWCNTs) catalyzed by previously deposited CaCO3 nanoparticles converts parallel graphene layers in a multiwall structure to aggregates formed by nano-onions with a diameter of 5–12 nm. The areas with positive curvature of graphene layers on the external surface of air-etched MWCNTs played the role of docking stations for nickel nanoparticles inserted by sonochemical deposition after removal of the CaCO3. The nickel nanoparticles were located exclusively at the tops of the onions. Formation of nanoscale curvature at the MWCNT support surfaces decreased the average size of Ni nanocrystals at similar loading of 50–60 wt% from 8 to 2 nm. Partial catalytic combustion did not change the concentration of surface carbonyl groups measured by titration, which attributes the observed phenomena directly to the corrugation of the MWCNT surfaces. The catalytic tests revealed a significant increase of catalytic activity of supported Ni catalyst due to corrugating of the external surface of the MWCNT support. After oxidative etching of the MWCNTs, the rate of chloroacetophenone hydrogenation measured with a Ni–MWCNT catalyst increased by a factor of 2 without change in selectivity yielding chlorophenylethanol as the main product.

Contribution of Nanoscale Curvature to Number Density of Immobilized DNA on Gold Nanoparticles

We report the curvature size dependence of the density of attached single-stranded DNA (ssDNA) on the surface of gold nanoparticles. The densities of immobilized ssDNA on 10, 20, 30, and 50 nm gold nanoparticles were examined, and we found that the maximum density of the immobilized ssDNA on 10 nm particles was 13 times larger than that on 50 nm particles, which was still 10 times larger than that on flat gold surfaces. This result indicates the importance of curvature in the nanometer-scale attachment of ssDNAs to nanoparticles.

Dynamic Variations in Adhesion of Self‐Assembled Monolayers on Nanoasperities Probed by Atomic Force Microscopy

Octadecyltriethoxysilane (OTE) self- assembled monolayers (SAMs) and their effects on friction and adhesion have been investigated on various combinations of functionalized and unfunctionalized silicon oxide surfaces including the oxidized surface of crystalline Si(100), silica nanoparticle films, and oxidized Si atomic force microscopy (AFM) tips. Force-distance spectroscopy was utilized to probe and compare the properties of the OTE SAMs on silica asperities with nanoscale curvature against these same monolayers on surfaces with sub-1 nm roughness (flat surfaces). It was found that adhesion between SAMs and silicon oxide surfaces can vary significantly when assembly takes place on surfaces with nanoscopic curvature as compared to flat surfaces. Observations indicate that the SAM structure present during force measurements is dynamic in nature, which yields different adhesion values when measured with variations of both tip-sample contact time and tip-approach/retract rates. These results point the need in reporting a number of measurement parameters when probing adhesion by SAM functionalized tips.

Electronic excitations in single-walled GaN nanotubes from first principles: Dark excitons and unconventional diameter dependences

We present the first ab initio predictions of electronic and excitonic states in gallium nitride nanotubes. Electron-hole interactions dramatically affect optical properties. Low-energy excitons are dark (dipole forbidden) in all nanotubes with key ramifications for applications. We describe an unusual decrease of energy gaps with decreasing nanotube diameter, opposing expectations from quantum confinement. This stems from a combination of nanoscale curvature and gallium chemistry, should apply to other systems, and furnishes an interesting way to reduce excitation energies with decreasing dimension.

Effect of Nanoscale Curvature of Single-Walled Carbon Nanotubes on Adsorption of Polycyclic Aromatic Hydrocarbons

Liquid-phase adsorption of tetracene and phenanthrene on a single-walled carbon nanotube (SWCNT) was examined. Tetracene adsorption was more than six times greater than that of phenanthrene. X-ray photoelectron spectroscopic examination clearly showed that tetracene and phenanthrene molecules efficiently coated the SWCNT external surfaces. The remarkable difference between the adsorption amounts of tetracene and phenanthrene was caused by the nanoscale curvature effect of the tube surface, resulting in a difference in the amount of contact between the molecule and the tube surface. The adsorption of tetracene and phenanthrene caused a significant higher frequency shift in the radial breathing mode (RBM) of the Raman band of the SWCNT, indicating an intensive pi-pi interaction between these polycyclic aromatic hydrocarbons and the external SWCNT surface.

Influence of nanoscale substrate curvature on growth kinetics and morphology of surface nuclei

Results on numerical modeling of the influence of a substrate’s nanoscale curvature on nucleation, growth kinetics, and morphological stability of nuclei during thin film vapor deposition are given. The problem is considered within the framework of the continuum surface diffusion equation taking into account the dependence of the adsorption energy, chemical potential, and the relevant surface mass fluxes on the surface curvature, together with the effect of surface self-shadowing from direct collisions from the gas phase and the contribution of readsorption fluxes. The nuclei growth kinetics are described by an Arrhenius type equation. Linear perturbation analysis of the growth model shows that positive nanoscale curvature (a concave surface) is able (i) to considerably increase the prenucleation concentration and thereby to increase the probability of nucleation and even to enable nucleation on substrates which do not have an affinity for nucleation under the given operating conditions, (ii) to increase considerably the growth rate of surface nuclei, and (iii) to lead to dramatic changes in morphology.

Influence of nanoscale surface curvature on prenucleation phenomena in chemical vapor deposition diamond growth

The problem of adsorption desorption of methyl radicals on a surface with nanoscale curvature is numerically studied for typical chemical vapor deposition diamond growth conditions. Surface profiles with concave nanoscale curvature lead to an increase in the energy of adsorption, which can enhance the nucleation of the new phase on the substrates. Moreover, the nanoscale curvature is even able to provoke a nucleation of the new phase on substrates which do not have an affinity for nucleation.