Anisotropic Aggregates Research Articles

Regulating interparticle proximity in plasmonic nanosphere aggregates to enhance photoacoustic response and photothermal stability.

Designing plasmonic nanoparticles for biomedical photoacoustic (PA) imaging involves tailoring material properties at the nanometer scale. A key in developing plasmonic PA contrast nanoagents is to engineer their enhanced optical responses in the near-infrared wavelength range, as well as heat transfer properties and photostability. This study introduces anisotropic plasmonic nanosphere aggregates with close interparticle proximity as photostable and efficient contrast agent for PA imaging. Silver (Ag), among plasmonic metals, is particularly attractive due to its strongest optical response and highest heat conductivity. Our results demonstrate that close interparticle proximity in silver nanoaggregates (AgNAs), spatially confined within a polymer shell layer, leads to blackbody-like optical absorption, resulting in robust PA signals through efficient pulsed heat generation and transfer. Additionally, our AgNAs exhibit a high photodamage threshold highlighting their potential to outperform conventional plasmonic contrast agents for high-contrast PA imaging over multiple imaging sessions. Furthermore, we demonstrate the capability of the AgNAs for molecular PA cancer imaging in vivo by incorporating a tumor-targeting peptide moiety.

Effects of steel bar and bi-directional erosion on chloride diffusion in reinforced concrete: A 3D mesoscale study

This work proposes a novel numerical framework to investigate 3D chloride diffusion behavior in reinforced concrete (RC). An efficient dynamic modeling approach is developed to generate the RC models with real-shaped aggregates at mesoscale. A semi-closed form solution of Fick’s second law is established to account for the time-varying chloride diffusion coefficient and surface chloride concentration through a genetic algorithm. Moreover, the effects of aggregate distribution and morphology on chloride diffusion are examined. The validated results demonstrate that the random distribution of aggregates leads to varied chloride concentration, and anisotropic aggregate morphology increases hindrance to chloride diffusion. Steel bar also affects chloride diffusion, causing an increase in chloride concentration on the steel surface. This hinder effect intensifies as the steel diameter increases and the protective layer thickness decreases. Additionally, bi-directional diffusion elevates chloride concentration on the corner steel surface, while smaller steel diameter and thicker protective layer render the corner steel bar more susceptible to bi-directional diffusion. The proposed framework has incorporated various influencing factors with comprehensive parametric analyses and holds potential for engineering design of RC structures considering durability, safety, and sustainability.

Graph convolutional network with tree-guided anisotropic message passing

Graph Convolutional Networks (GCNs) with naive message passing mechanisms have limited performance due to the isotropic aggregation strategy. To remedy this drawback, some recent works focus on how to design anisotropic aggregation strategies with tricks on feature mapping or structure mining. However, these models still suffer from the low ability of expressiveness and long-range modeling for the needs of high performance in practice. To this end, this paper proposes a tree-guided anisotropic GCN, which applies an anisotropic aggregation strategy with competitive expressiveness and a large receptive field. Specifically, the anisotropic aggregation is decoupled into two stages. The first stage is to establish the path of the message passing on a tree-like hypergraph consisting of substructures. The second one is to aggregate the messages with constrained intensities by employing an effective gating mechanism. In addition, a novel anisotropic readout mechanism is constructed to generate representative and discriminative graph-level features for downstream tasks. Our model outperforms baseline methods and recent works on several synthetic benchmarks and datasets from different real-world tasks. In addition, extensive ablation studies and theoretical analyses indicate the effectiveness of our proposed method.

Structure Regulation of Sodium Ion on Nanosilica Growth Visualized Using 29Si Nuclear Magnetic Resonance Spectroscopy

Understanding the action mechanism of sodium ions in sodium silicate solutions is necessary for the synthesis of nanosilica. The microstructure of sodium silicate solutions with SiO2:Na2O ratios ranging from 2 to 4 was characterized by 29Si nuclear magnetic resonance spectroscopy, and the magnetic shielding tensor of the nuclear magnetic field was calculated using the density functional theory. Sodium ions contribute significantly to the magnetic shielding tensor, thereby playing a key role in the structural evolution of sodium silicate solution species. Wave function analysis was used to further study the mechanism of action of sodium ions. Theoretical calculation results show that Na not only affects the magnetic shielding and regulates the splitting and change of NMR peaks but also regulates the aggregation-free energy and growth morphology of silica nanoparticles. Thus, the structural regulation of sodium ions on nanosilica growth and aggregation was proposed. Magnetic shielding caused by partial symmetry disappears with the reduction of sodium ions in the system, resulting in uniform magnetic shielding. Meanwhile, the anisotropic aggregation free energy of microscopic particles tends to be isotropically distributed, resulting in the spherical growth tendency of the nanosilica particles. Small-angle X-ray scattering and transmission electron microscopy were used to verify these conclusions. In this work, we adopted the leading quantum chemical computational methods with advanced computer technology and quantum chemical methods to research the microscopic effect of sodium ions during nanosilica growth, thereby overcoming the limitations of the analytical experience and paradigm established with traditional organic chemistry and providing important theoretical reference value for the field of spectral systems and characterization measurement methods. At the same time, the reasonable mechanism of action is proposed, which greatly expands the product application field of nanosilica.

Integrating the traffic science with representation learning for city-wide network congestion prediction

Recent studies on traffic congestion prediction have paved a promising path towards the reduction of potential economic and environmental loss. However, at the city-wide scale, current approaches face substantial hurdles, such as being unable to support the multiple sensors modalities, insufficient congestion fluctuation and propagation modeling, and weak generalization to heterogeneous traffic network structures. To address these pitfalls, this paper investigates how to integrate the missing urban science domain priors into a general sequential prediction model, and proposes the customized Traffic-informed Transformer (TinT). To prevent receptive field bias, a novel mixture of long and short range information routing mechanism is proposed with the traffic-informed tokenization. To capture the unbalanced traffic flow propagation, an original anisotropic graph aggregation is developed to differentiate the traffic fluctuation based on orientations. Extensive results demonstrated TinT’s outstanding performance over other twelve state-of-the-art models and its broad applicability to multiple data modalities in six well-known cities throughout the world. We released our implementations at: https://github.com/VITA-Group/TinT.

Dumbbells, chains, and ribbons: anisotropic self-assembly of isotropic nanoparticles.

Functionalizing the surface of metal nanoparticles can assure their stability in solution or mediate their self-assembly into aggregates with controlled shapes. Here we present a computational study of the colloidal aggregation of gold nanoparticles (Au NPs) isotropically functionalized by a mixture of charged and hydrophobic ligands. We show that, by varying the relative proportion of the two ligands, the NPs form anisotropic aggregates with markedly different topologies: dumbbells, chains, or ribbons. In all cases, two kinds of connections keep the aggregates together: hydrophobic bonds and ion bridges. We show that the anisotropy of the aggregates derives from the NP shell reshaping due to the formation of the hydrophobic links, while ion bridges are accountable for the "secondary structure" of the aggregates. Our findings provide a general physical principle that can also be exploited in different self-assembled systems: anisotropic/directional aggregation can be achieved starting from isotropic objects with a soft, deformable surface.

Effect of charge and anisotropic diffusivity on ion exchange kinetics in nuclear waste form materials

Motifs of radionuclide absorption particles (absorbers or fillers) for the nuclear waste treatment usually have crystal structures with nano-sized tunnels for fast ion diffusion. On the other hand, the accumulation of ions generates an electric field which affects the ion diffusion. Therefore, the strong anisotropic kinetic properties and the electric field affect ion exchange kinetics, especially in an assembly of these particles which may block the fast diffusion tunnels for each other. In this work, we developed a mesoscale model to describe the effect of anisotropic kinetic properties and electric field on ion exchange kinetics. With the model we simulated the effect of anisotropic diffusivity, electrochemical potential, particle morphology, size and aggregation on ion exchange kinetics during batch experiments. It is found that (1) ion exchange results in charge accumulation inside the particle because different ions have different diffusivities and different diffusion driving forces. The electric neutrality is not preserved; (2) the electric field speeds up the slower diffusion ions (either uptake or release) and slows down the faster diffusion ions to reduce charge accumulation and maintains charge neutrality; (3) the ion exchange becomes very slow at the later stages because (a) diffusion driving force (electrochemical gradient, Cs+ concentration in the solution and Na+ inside the particle) continuously decreases, as observed in batch experiments; and (b) the diffusivity decreases due to the Cs+ concentration dependence of ion diffusivity. This can explain the observed experimental phenomena that the radionuclide capacity usually cannot be reached; (4) for needle-like particle and their clusters, both surface area and diffusion distance along the direction with the fastest diffusivities have significant impact on the ion exchange kinetics.

Not All Voxels Are Equal: Semantic Scene Completion from the Point-Voxel Perspective

We revisit Semantic Scene Completion (SSC), a useful task to predict the semantic and occupancy representation of 3D scenes, in this paper. A number of methods for this task are always based on voxelized scene representations. Although voxel representations keep local structures of the scene, these methods suffer from heavy computation redundancy due to the existence of visible empty voxels when the network goes deeper. To address this dilemma, we propose our novel point-voxel aggregation network for this task. We first transfer the voxelized scenes to point clouds by removing these visible empty voxels and adopt a deep point stream to capture semantic information from the scene efficiently. Meanwhile, a light-weight voxel stream containing only two 3D convolution layers preserves local structures of the voxelized scenes. Furthermore, we design an anisotropic voxel aggregation operator to fuse the structure details from the voxel stream into the point stream, and a semantic-aware propagation module to enhance the up-sampling process in the point stream by semantic labels. We demonstrate that our model surpasses state-of-the-arts on two benchmarks by a large margin, with only the depth images as input.

Interplay of Solid–Liquid Interactions and Anisotropic Aggregation in Solution: The Case Study of γ-AlOOH Crystallites

The development of original nanoparticle size and shape requires a detailed knowledge and rationalization of the formation mechanism. A consolidated mechanism of γ-AlOOH boehmite nanorod formation ...

Supramolecular Polymerization of C3-Symmetric, Triphenylene-Cored Aza-Polycyclic Aromatic Hydrocarbons with Excellent and Switchable Circularly Polarized Luminescence Performance

A new type of C3-symmetric aza-polycyclic aromatic hydrocarbon (PAH) discs attached with chiral alkoxyl chains is developed and explored as circularly polarized luminescence (CPL)-active materials with selective control and switching of chiroptical properties. Supramolecular polymerization of these PAHs is studied experimentally and theoretically. With the aid of weak hydrogen bonding and CH···π interactions, these chromophores have strong tendency to form anisotropic chiral aggregates both in solutions and films. The well-controlled noncovalent interactions are critical for their excellent CPL performance. The resultant supramolecular polymers display a polarized emission band with the maximum glum value up to 10–2. Benefited from the chiral supramolecular polymerization process and N-doping structure feature of the core, on/off CPL switching from these molecules can be reversibly realized by external stimuli including the change of temperature, solvent, and pH conditions. Our work shows that chiral supramolecular polymers from concise yet highly rigid and planar PAH cores are superbly suitable for exceptional CPL emission both in dilute solutions and bulk materials, with a promising switchable CPL feature, thereby unlocking new design possibilities.

Effect of temperature on the growth of TiN thin films by oblique angle sputter-deposition: A three-dimensional atomistic computational study

Kinetic Monte Carlo (kMC) atomistic computations using MODENA code were employed to simulate the growth of columnar TiN thin films under oblique angle deposition geometry. The influence of substrate temperature (300, 400 and 500 K) on the morphology (column tilt angle, average layer density, compactness, surface roughness) of the layers was studied by varying the inclination angle α of the substrate from 5° to 85° with respect to the centerline of the source. Two types of simulations were considered in this work: the first one assumes a collimated flux (CF) of incident particles and the second one grasps the angular distribution of sputtered Ti particles to closely mimic the magnetron sputtering (MS) conditions. The formation of separated columns with high aspect ratio, and tilted in the direction of the incident particles flux, is observed for α ≥ 35° for the two types of particle flux. The column width and tilt angle, the average layer density and the compactness of the TiN films are found to increase with increasing substrate temperature, due to enhanced surface diffusion. The column tilt angle β increases from 3° to 60° with increasing α for the CF case, while it saturates to approx. 35° when the MS distribution is considered. The relationship between β and α, and their temperature dependence, are discussed and compared to experimental results obtained on sputter-deposited TiN films, as well as with other results and models reported in the literature. The code also reproduces morphological features common to most films produced at glancing angles, such as column broadening with increasing thickness and their anisotropic aggregation (bundling association) in the transverse direction.

Ligament-Inspired Tough and Anisotropic Fibrous Gel Belt with Programed Shape Deformations via Dynamic Stretching.

Nature provides perpetual inspiration for exploring anisotropic materials to implement complex functions and motions like biological organisms. In particular, fibrous hydrogel-based anisotropic aggregates have attracted tremendous interest as fantastic materials for development into artificial ligaments or muscles. Such aggregates combine the structural anisotropy and macroscopic flexibility of fiber materials, with the intelligence, softness, and wetness of hydrogel materials. However, controlled fabrication of such hydrogels with aligned microstructures, even in a macroscopic level, remains a challenge. Here, a facile and general strategy was proposed to develop ligament-inspired multistructural (mono/bilayer) gel belts via dynamic stretching of multistrand pregels, accompanied by the simultaneous assembly of hydrogel fibers. The resultant gel belts evolved into anisotropic and aligned micro- and macrostructures, exhibiting high elastic moduli (0.01-23.5 MPa) and unique anisotropic swelling behaviors. Through further physical and chemical structure design, bioinspired multiple fibrous gel-based actuators were developed to achieve anisotropic, relatively fast (within 60 s), and delicate macroscopic shape deformations. This work provides a great platform for the design and construction of next-generation soft materials for biomimetic tissues.

Structure and dynamics of an aqueous solution containing poly-(acrylic acid) and non-ionic surfactant octaethylene glycol n-decyl ether (C10E8) aggregates and their complexes investigated by molecular dynamics simulations.

A detailed molecular dynamics simulation study of the self-assembly, intermolecular structure and thermodynamic behavior of an aqueous solution of non-ionic surfactant octa ethylene glycol n-decyl ether (C10E8) in the presence of a non-ionic polar polymer poly(acrylic acid) PAA is presented. The aggregation number Nagg and concentration of surfactant Cs in the simulation systems were varied in the range 0.01-0.32 M and 5 < Nagg < 101 (dilute to concentrated) with a dilute polymer concentration (Cp = 0.01 M). Lamellar aggregates of non-ionic surfactant in bulk aqueous solution are shown by molecular level computations for the first time. Spherical micellar aggregates and lamellar aggregates are formed at low and high Nagg, respectively. The transition from the spherical micelle phase to the lamellar phase in a binary solution is captured for the first time. A conformational transition from coiled to extended PAA chains adsorbed on the surfactant aggregate occurs at a particular value of Nagg, commensurate with the transition from spherical micelle aggregates to anisotropic lamellar aggregates. Formation of the surfactant aggregate in binary and ternary solutions and the polymer-surfactant complex in a ternary solution is enthalpically favored. Adsorption of PAA on the surfactant aggregate surface is driven by hydrogen bonds (HBs) between carboxylic acid groups of PAA and ethylene oxide groups of C10E8. A significant number of HBs occur between polar oxygens of C10E8 and hydroxyl oxygens of PAA. The results are in agreement with the limited available experimental data on this system.

Equilibria of an anisotropic nonlocal interaction equation: Analysis and numerics

In this paper, we study the equilibria of an anisotropic, nonlocal aggregation equation with nonlinear diffusion which does not possess a gradient flow structure. Here, the anisotropy is induced by an underlying tensor field. Anisotropic forces cannot be associated with a potential in general and stationary solutions of anisotropic aggregation equations generally cannot be regarded as minimizers of an energy functional. We derive equilibrium conditions for stationary line patterns in the setting of spatially homogeneous tensor fields. The stationary solutions can be regarded as the minimizers of a regularised energy functional depending on a scalar potential. A dimension reduction from the two- to the one-dimensional setting allows us to study the associated one-dimensional problem instead of the two-dimensional setting. We establish $\Gamma$-convergence of the regularised energy functionals as the diffusion coefficient vanishes, and prove the convergence of minimisers of the regularised energy functional to minimisers of the non-regularised energy functional. Further, we investigate properties of stationary solutions on the torus, based on known results in one spatial dimension. Finally, we prove weak convergence of a numerical scheme for the numerical solution of the anisotropic, nonlocal aggregation equation with nonlinear diffusion and any underlying tensor field, and show numerical results.

DEM simulation of anisotropic granular materials: elastic and inelastic behavior

In this work, Discrete Elements Method simulations are carried out to investigate the effective stiffness of an assembly of frictional, elastic spheres under anisotropic loading. Strain probes, following both forward and backward paths, are performed at several anisotropic levels and the corresponding stress is measured. For very small strain perturbations, we retrieve the linear elastic regime where the same response is measured when incremental loading and unloading are applied. Differently, for a greater magnitude of the incremental strain a different stress is measured, depending on the direction of the perturbation. In the case of unloading probes, the behavior stays elastic until non-linearity is reached.Under forward perturbations, the aggregate shows an intermediate inelastic stiffness, in which the main contribution comes from the normal contact forces. That is, when forward incremental probes are applied the behavior of anisotropic aggregates is an incremental frictionless behavior. In this regime we show that contacts roll or slide so the incremental tangential contact forces are zero.Graphical

Anomalous Anisotropic Nanoparticle Aggregation in Cu2(OH)3Br Gels.

Aerogels are of interest for their ability to uniformly incorporate nanoscale features into macroscopic assemblies, which enabled applications that require low density, high surface area, and/or bicontinuous networks. The structure of the nanoporous network is intrinsically linked to the macroscopic properties of aerogels. Hence, control of this structure is of paramount importance. Small-angle X-ray scattering (SAXS) is used here to monitor nanoparticle aggregation in situ in Cu2(OH)3Br aerogels formed via epoxide-assisted gelation. Anomalous anisotropic aggregation is observed in the absence of templating agents and is attributed to the molecular structure of the inorganic nanoparticles themselves. This is a fundamental departure from the models currently used to describe traditional inorganic sol-gel chemistry where nanoparticles are believed to undergo isotropic diffusion- and/or kinetically limited aggregation. Time-resolved SAXS indicates that Cu2(OH)3Br nanoparticles nucleate rapidly from solution to form unbranched chain-like aggregates rather than branched mass-fractal aggregates. Sizes of primary particles (∼1.5 nm) and the chain-like structure of their aggregates are independent of particle concentration (gel density), while rates of particle aggregation, gelation time, and aggregate size are strongly dependent upon particle concentration, which implies that the chemistry of particle formation and the physics of particle aggregation are independent processes. Because the conditions necessary for creating anisotropic structures are not unique to Cu2(OH)3Br, these results could provide insight into the structure and gelation mechanisms of other inorganic aerogels.

Electrical Conductivity of Field-Structured Emulsions

The structure formation influence on various macroscopic properties of fluid–fluid disperse systems is poorly investigated. The present work deals with the experimental study of the charge transfer in emulsions whose dispersed phase droplets are arranged into chainlike structures under the action of an external force field. The emulsions studied are the fluid system in which water droplets are dispersed in a hydrocarbon-based magnetic fluid. Under the effect of an external uniform magnetic field, anisotropic aggregates form from the emulsion dispersed phase drops. The low-frequency electrical conductivity of emulsions has been measured. It is demonstrated that the emulsions’ conductivity grows several times under the effect of magnetic field parallel to the measuring electrical field. The anisotropic character of the emulsion electrical conductivity in the presence of magnetic field has been demonstrated. It is revealed that the maximal response of conductivity on the magnetic field action takes place at the dispersed phase volume fraction of about 20%. The dynamics of the conductivity variation is analyzed in dependence on the magnetic field strength and the dispersed phase volume fraction. The obtained results may be of interest in the development of potential applications of disperse systems with magnetic-field-controllable properties.

Nonlinearly Elastic Constitutive Relation of Anisotropic Aggregate of Cube Crystallites

Under Voigt model, Barsch and Johnson gave the formula of nonliearly elastic constitutive relations for isotropic aggregates of cubic crystallites and orthorhambic aggregates of cubic crystallies, respectively. In this paper, a nonlinear elastic constitutive relation based on Voigt model, which is more general than Barsch's and Johnson's results, is derived for the set of anisotropic cubic grains. The anisotropy of metals is described by the texture coefficient.

Temperature compensated three-dimension fiber optic vector magnetic field sensor based on an elliptical core micro fiber Bragg grating.

In this paper, a temperature-compensated three-dimension vector fiber optic magnetic field sensor based on an elliptical core micro fiber Bragg grating (FBG) has been proposed and experimentally demonstrated. The elliptical core fiber was tapered to form a microfiber, in which a FBG was inscribed. Due to the magnetism-manipulation of the anisotropic aggregation of ferromagnetism nanoparticles around the fiber surface, the effective refractive index of the evanescent field for two orthogonal polarization modes was modulated, and the magnetic field orientation can be detected by interrogating the wavelength interval between two reflection peaks. However, two reflection peaks show the identical response to ambient temperature. Hence the proposed sensor can achieve the measurements of the magnetic field intensity and the orientation simultaneously without the temperature cross-sensitivity. The experimental results show that the magnetic field orientation sensitivity of 15 pm/deg and intensity sensitivity of 81 pm/mT can be achieved, and the maximum standard variation of the temperature cross-sensitivity is only 0.02 nm. The proposed elliptical core micro FBG appears to have potential applications in navigation, vehicle detection, and current sensing.

The influence of directed hydrogen bonds on the self-assembly of amphiphilic polymers in water

HypothesisMolecules forming directed intermolecular hydrogen bonds, such as the well-known benzene-1,3,5-tricarboxamides (BTA) motif, are known to self-assemble into long fibrous structures. However, only a few of these systems have so far demonstrated the ability to form such anisotropic nanostructures, if they are combined with hydrophilic polymers to create an amphiphilic material. Here, we designed BTA-polymer conjugates to investigate whether the directionality of the hydrogen bonds or the ratio of hydrophobic to hydrophilic parts of the molecule, and thus the packing parameter, is decisive for obtaining anisotropic supramolecular structures in water. ExperimentsPoly(ethylene glycol) was conjugated to BTA moieties with varying lengths of hydrophobic alkyl spacers ranging from two to twelve methylene units. The resulting amphiphilic materials were characterized in aqueous solution by light and small-angle neutron scattering, analytical ultracentrifugation, and cryo-transmission electron microscopy. FindingsWhile spherical micelles were observed for C6 and C10 alkyl spacers, anisotropic structures were only present in case of the C12 spacer. The comparison to an analogous material, which lacks the directed hydrogen bonds, revealed that the BTA motif cannot provide a sufficient driving force to induce anisotropic structures, but increases the packing density in the hydrophobic part. Therefore, the packing parameter governs the appearance of anisotropic aggregates.