Alignment Of Particles Research Articles

Nanoparticle localization within chiral liquid crystal defect lines and nanoparticle interactions.

Self-assembly of colloidal particles into predefined structures is a promising way to design inexpensive manmade materials with advanced macroscopic properties. Doping of nematic liquid crystals (LCs) with nanoparticles has a series of advantages in addressing these grand scientific and engineering challenges. It also provides a very rich soft matter platform for the discovery of unique condensed matter phases. The LC host naturally allows the realization of diverse anisotropic interparticle interactions, enriched by the spontaneous alignment of anisotropic particles due to the boundary conditions of the LC director. Here we demonstrate theoretically and experimentally that the ability of LC media to host topological defect lines can be used as a tool to probe the behavior of individual nanoparticles as well as effective interactions between them. LC defect lines irreversibly trap nanoparticles enabling controlled particle movement along the defect line with the use of a laser tweezer. Minimization of Landau-de Gennes free energy reveals a sensitivity of the ensuing effective nanoparticle interaction to the shape of the particle, surface anchoring strength, and temperature, which determine not only the strength of the interaction but also its repulsive or attractive character. Theoretical results are supported qualitatively by experimental observations. This work may pave the way toward designing controlled linear assemblies as well as one-dimensional crystals of nanoparticles such as gold nanorods or quantum dots with tunable interparticle spacing.

Comparative study on packing arrangement of irregular gadolinium inside active magnetic regenerators in a magnetic refrigeration system

In this study, we investigate two types of active magnetic regenerators (AMRs) including non-aligned and aligned particles of irregular gadolinium and verify their effect on the performance of a magnetic refrigeration system. The aligned AMRs were packed with irregular particles under the external magnetic field to line them up, while the non-aligned AMRs without the magnetic field during their preparation. According to the X-ray computed tomography, the particles were observed to be arranged in parallel to the flow direction in the aligned AMRs whereas they were randomly located in the non-aligned ones. The pressure drop by the aligned AMRs was 18.8 % smaller than that by the non-aligned ones when heat transfer fluid flowed, which was deionized water with 3 vol% of anti-corrosive additive. Moreover, the friction factor for the aligned AMRs was 35.9 % smaller than that for the non-aligned ones on average, which was even 20.5 % lower than the ones with spheres estimated by the Carman correlation. Meanwhile, the coefficient of performance of the aligned AMRs was improved by 37.3 %, 27.3 %, and 10.5 % in 0.56, 0.71, and 1.00 Hz of the nominal operating frequencies in the system with 4.5 K of the temperature span. This enhancement was mainly attributed to the power consumption by the pump which declined by 8.9 %, 16.4 %, and 9.4 % on average at each nominal operating frequency by using the aligned AMRs.

Femtosecond Laser Micromachining of the Mask for Acoustofluidic Device Preparation.

Surface acoustic wave (SAW)-based acoustofluidic devices have shown broad applications in microfluidic actuation and particle/cell manipulation. Conventional SAW acoustofluidic device fabrication generally includes photolithography and lift-off processes and thus requires accessing cleanroom facilities and expensive lithography equipment. In this paper, we report a femtosecond laser direct writing mask method for acoustofluidic device preparation. By micromachining of steel foil to form the mask and direct evaporation of metal on the piezoelectric substrate using the mask, the interdigital transducer (IDT) electrodes of the SAW device are generated. The minimum spatial periodicity of the IDT finger is about 200 μm, and the preparation for LiNbO3 and ZnO thin films and flexible PVDF SAW devices is verified. Meanwhile, we have demonstrated various microfluidic functions, including streaming, concentration, pumping, jumping, jetting, nebulization, and particle alignment using the fabricated acoustofluidic (ZnO/Al plate, LiNbO3) devices. Compared to the traditional manufacturing process, the proposed method omits spin coating, drying, lithography, developing, and lift-off processes and thus has advantages of simple, convenient, low cost, and environment friendliness.

MIDLS - Membrane detection in cryo-EM using deep level sets.

Studying membrane proteins (MP) with their membranes is more biologically relevant and allows for functional and structural studies to be performed in the same system. However, the presence of membranes in cryogenic-Electron Microscopy (cryo-EM) imaging data limits particle identification and alignment. The variability and strong contrast of membranes override the weaker particle signal. To address these limitations, researchers are forced to either extract MPs from their membrane before imaging, preventing functional studies; or digitally subtract membranes, requiring user intervention to detect membranes.

Intrinsic fiducials for small membrane protein structure determination.

Solute carrier proteins (SLC) are small membrane transport proteins that play a critical role in many physiological processes. Despite their critical importance, our understanding of how these proteins function is limited due to the difficulty of structure determination. This is particularly true for major facilitator superfamily (MFS) proteins where there are often limited protein features to drive computational alignment of particles. While tools like cryo-EM have greatly enhanced the ability to determine membrane protein structures, fiducial markers are needed to help promote particle alignment. Fragment antigen-binding antibodies (Fab) or nanobodies (Nb) are the most commonly used examples, but generating these is not a trivial task. Often this is the largest barrier for membrane protein structure determination, taking a significant amount of time and resources. In the end, the resulting fiducial may be too flexible to enable high resolution structure determination, requiring the whole process to be done again. A feature intrinsic to the protein sequence would eliminate this barrier as it would require no additional generation time, and can be purified concurrently with the transporter of interest. Here we investigate the use of an intrinsic fiducial consisting of GFP and anti-GFP Nb labeled at the each of the protein's termini to solve a novel structure of an MFS transporter. We have generated three fully functional constructs, each with varying termini lengths, and demonstrated successive improvements in fiducial rigidity and cryo-EM reconstructions. We believe this method will not only enable us to solve a previously unknown structure, but also prove to be an accessible means for membrane protein structure determination.

Dynamic phases and combing effects for elongated particles moving over quenched disorder.

We consider a two-dimensional system of elongated particles driven over a landscape containing randomly placed pinning sites. For varied pinning site density, external drive magnitude, and particle elongation, we find a wide variety of dynamic phases, including random structures, stripe or combed phases with nematic order, and clogged states. The different regimes can be identified by examining nematic ordering, cluster size, number of pinned particles, and transverse diffusion. In some regimes we find that the pinning can enhance the particle alignment, producing a nonmonotonic signature in the nematic ordering with a maximum at a particular combination of pinning density and drive. The optimal nematic occurs when a sufficient number of particles can be pinned, generating a local shear and leading to what we call a combing effect. At high drives, the combing effect is reduced when the number of pinned particles decreases. For stronger pinning, the particles form a heterogeneous clustered or clogged state that depins into a fluctuating state with high diffusion.

Particle alignment effects on mechanical properties of cellulose nanocrystal thin films

The fracture mechanics of cellulose nanocrystal (CNC) thin films are strongly dependent on their alignment direction relative to the loading direction.

Investigation on permeability anisotropy in unconsolidated hydrate-bearing sediments based on pore-scale numerical simulation: Effect of mineral particle shape and pore-filling

Resulting from the preferential alignment of sediment particles, permeability anisotropy of unconsolidated strata is an essential parameter for natural gas hydrate (NGH) exploitation. Fundamentally, the effect of mineral particle shape and pore-filling NGH on the permeability anisotropy are considered in this study. A simulation with combining methods of particle flow code and computational fluid dynamics is conducted to construct a series of numerical samples and calculate the anisotropic permeabilities. Different particles shapes and hydrate saturations are preinstalled in these samples. It is firstly proved that the elongated particles have little effect on permeability anisotropy. Meanwhile, the preferential alignment of plate-shaped particles is the main reason for permeability anisotropy. In principle, the difference between intermediate orthogonal axes and short orthogonal axes of plate-shaped particles makes the tortuosity different in directions, thus inducing the permeability anisotropy. The anisotropy ratio decreases with the increase of hydrate saturation, which is caused by the nonlinear decline of main channel flow resulting from the thrombus-like hydrate particles. The results provide an insight into the formation mechanism of permeability anisotropy and display potential application value in NGH exploitation, groundwater environment protection and geological disaster prevention.

Microscopic field theory for structure formation in systems of self-propelled particles with generic torques.

We derive a dynamical field theory for self-propelled particles subjected to generic torques and forces by explicitly coarse-graining their microscopic dynamics, described by a many-body Fokker-Planck equation. The model includes both intrinsic torques inducing self-rotation, as well as interparticle torques leading to, for instance, the local alignment of particles' orientations. Within this approach, although the functional form of the pairwise interactions does not need to be specified, one can directly map the parameters of the field theory onto the parameters of particle-based models. We perform a linear stability analysis of the homogeneous solution of the field equations and find both long-wavelength and short-wavelength instabilities. The former signals the emergence of a macroscopic structure, which we associate with motility-induced phase separation, while the second one signals the growth of a finite structure with a characteristic size. Intrinsic torques hinder phase separation, pushing the onset of the long-wavelength instability to higher activities. Furthermore, they generate finite-sized structures with a characteristic size proportional to both the self-propulsion velocity and the inverse of the self-rotation frequency. Our results show that a general mechanism might explain why chirality tends to suppress motility-induced phase separation but instead promotes the formation of non-equilibrium patterns.

Shape-dependent regions for inertialess spheroids in turbulent channel flow

The alignment between the inertialess spheroids and the directions of the fluid Lagrangian stretching or compression is sensitive to the particles shape near the wall but not near the center of the channel [Cui et al. “Alignment statistics of rods with the Lagrangian stretching direction in a channel flow,” J. Fluid Mech. 901, A16 (2020)]. This observation is further investigated in the current study to uncover the mechanism of particle alignment behavior in different regions of channel flows at Reτ≈180 and 1000. Meanwhile, by using the probability distributions of the sign of the discriminant of the linear term in the Jeffery equation, we find that the turbulent channel flow can be distinctly divided into strong and weak shape-dependent regions. In the weak shape-dependent region, the slender (flat) particles have extraordinarily similar alignments with the directions of fluid Lagrangian stretching (compression). However, in the strong shape-dependent region, the alignments of these inertialess particles are sensitive to the particles shape, especially with the particle positions approaching the wall. The ranges of these shape-dependent regions rely on the Reynolds number, but the probability distributions of the sign of the discriminant of the linear term in the Jeffery equation are a useful tool to distinguish these shape-dependent regions in the wall turbulence regardless of the Reynolds number.

Oriented arrangement of carbon black particles achieved via in situ polymerization and microfibrillation process

Effective dispersion and oriented arrangement of filler particles are crucial to improve the efficiency of filler for improving the mechanical and functional performance of fiber materials. However, how to control the alignment of isotropic (spherical) particles in the melt spinning process is still a challenge. In this work, the distribution of carbon black (CB) particles in Polymethyl methacrylate/polyacrylate@modified carbon black (PMMA/PAcr@MCB) composite were investigated. The results show that the effective dispersion and oriented arrangement of CB particles were achieved when CB particles were encapsulated in PAcr microspheres firstly and then blended with PMMA via in situ microfibrillation. This is ascribed to the distribution of CB particles was confined in the PAcr microfibril phase and rearranged into oriented arrangement after stretching process. Compared to neat PMMA, the elongation at break and fracture energy of PMMA/PAcr@MCB were increased by ~380% and 438%, respectively. Theses increasements are attributable to the high aspect ratio and small diameter of PAcr@MCB microfibrils. The findings in this work provide new enlighten to control the alignment of isotropic particles to improve filler efficiency and avoid big aggregation for preparing materials like fine fibers or thin films.

Predicting particle orientation: Is an accurate flow field more important than the actual orientation model?

Analytical orientation prediction models (OPMs) are widely applied to efficiently predict the orientation of particles in suspensions or pastes. One application of these prediction models are extrusion processes where the model is used to identify combination of process and paste parameters that yield anisotropic orientation within the extruded filament. The accuracy of these predictions mainly depends on two elements that are the correct choice of the orientation model itself and the rheology model. The rheology of a paste is commonly modeled with the help of the Herschel Bulkley (HB) rheology model. The optimal OPM is still topic of today’s research. Which of the two elements, however, has a stronger influence on the orientation has not been addressed, yet. We make use of a wide range of HB parameters reported in literature with a particular focus on data that is reported for varying paste compositions. Based on this data, we use the HB model to predict the velocity and shear rate profile within a pipe and perform orientation predictions with the help of the models by Jeffery and Folgar and Tucker (FT). These predictions are used to estimate the sensitivity of the final orientation on the HB parameters and on the OPM. For our study, we assume that the paste can be described by the standard Herschel Bulkley rheology model. We assume no-slip boundary conditions and no influence of the particle orientation on the rheology. Second, we assume that the initial particle orientation before entering the pipe is random. Our results suggest that capturing the rheology model correctly is generally more important than capturing the OPM correctly. This applies in particular when densely filled states are approached. We also provide universal relations for predicting the degree of particle alignment and the mean flow velocity as functions of process parameters and material properties. • A suitable rheology model is found to be more important than the actual orientation prediction model in terms of particle orientation. • Normalized diagrams enable quick estimations of the evolution of particle orientation based on process parameters and paste properties. • The derived methodology is applied to a large set of published rheology data.

Combined Influence of Particle Shape and Fabric on the Shear Behaviour of Granular Materials

The anisotropy feature is an important characteristic of granular materials in natural life and is caused by two facts: the anisotropy feature of particle shape, such as an elongated or flattened shape, and the anisotropy feature of the packing fabric, such as the preferable orientation of particle alignment. The discrete element method has been commonly used in the study of meso-mechanics of granular materials and is in our study to simulate the direct shear test with particles of various aspect ratios under different initial orientation alignment conditions for assessing the coupled influence of anisotropy from particle shape and fabric of particle packings on the shear behaviour of granular materials. Analysis results show that anisotropy from the particle shape has the most significant influence on the shear behaviour of a granular packing when the packing has the initial anisotropy fabric of an orientational alignment perpendicular to the shear direction. Moreover, the initial fabric anisotropy of a granular packing has an increasing influence with the rise in anisotropy of particle shape. A combined anisotropic factor is finally introduced to reflect the coupled influence of the shape anisotropy of particles and the fabric anisotropy of particle packings.

Improved properties of polyvinyl alcohol films blended with aligned nanocellulose particles induced by a magnetic field

In this study, polyvinyl alcohol (PVA) films filled with nanocellulose particles were developed for food packaging. In particular, the effect of the weak magnetic field-induced alignment of the nanocellulose filler in PVA blended with rod-shaped cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) on the physicochemical properties of the respective blends was investigated. For the alignment of the nanocellulose particles (6% with respect to PVA), a film-forming solution of each blend was cast and a homogeneous magnetic field of the order of milli Tesla was applied during drying. Microscopic investigations were conducted to analyze the dispersion of the CNCs and CNFs in the PVA matrix. The influence of particle alignment was examined in terms of the microstructure, intermolecular interactions, crystallinity, and hydration state of the film, as well as water migration. The applied magnetic field induced the orientation of the nanocellulose fillers, leading to their improved dispersion in the PVA matrix. The uniform structure formed owing to the magnetically induced alignment of nanocellulose led to enhanced mechanical, barrier, and hydrophobic properties, as well as thermal stability of the two blends. The improvement was more evident for the CNC/PVA blend compared to the CNF/PVA one. The applied magnetic field decreased the fluidity of the film and increased the number of water molecules bound to PVA. When applied in the preservation of strawberries, the films exposed to a magnetic field facilitated better protection and firmness of the fruit.

Structure of the human heterodimeric transporter 4F2hc-LAT2 in complex with Anticalin, an alternative binding protein for applications in single-particle cryo-EM

Cryo-EM structure determination of relatively small and flexible membrane proteins at high resolution is challenging. Increasing the size and structural features by binding of high affinity proteins to the biomolecular target allows for better particle alignment and may result in structural models of higher resolution and quality. Anticalins are alternative binding proteins to antibodies, which are based on the lipocalin scaffold and show potential for theranostic applications. The human heterodimeric amino acid transporter 4F2hc-LAT2 is a membrane protein complex that mediates transport of certain amino acids and derivatives thereof across the plasma membrane. Here, we present and discuss the cryo-EM structure of human 4F2hc-LAT2 in complex with the anticalin D11vs at 3.2 Å resolution. Relative high local map resolution (2.8–3.0 Å) in the LAT2 substrate binding site together with molecular dynamics simulations indicated the presence of fixed water molecules potentially involved in shaping and stabilizing this region. Finally, the presented work expands the application portfolio of anticalins and widens the toolset of binding proteins to promote high-resolution structure solution by single-particle cryo-EM.

Magnetic‐Oriented Nickel Particles and Nickel‐Coated Carbon Nanotubes: An Efficient Tool for Enhancing Thermal Conductivity of PDMS Composites

AbstractIn this study, PDMS composites are thermally cured with nickel particles and nickel‐coated carbon nanotubes as fillers. Both fillers are oriented with the aim to increase the thermal conductivity of the silicone polymer network, due to the formation of a continuous thermal path. Scanning electron microscopy (SEM) gives a picture of the polymer network's morphology, proving the effective alignment of the nickel particles. Rheology and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR) studies confirm the full curing of the silicon network and no influence in the curing kinetics of the type and content of fillers and their orientation. Dynamic mechanical thermal analysis (DMTA) and tensile analysis show instead different thermo‐mechanical behavior of the polymer network due to the presence of different fillers, different fillers percentage, and orientation. Finally, the thermal transmittance coefficient (k) is studied by means of hot disk analysis, revealing the increment of almost 200% due to magnetic filler orientation.

In-situ alignment of 3D printed anisotropic hard magnets

Within this work, we demonstrate in-situ alignment of the easy axis single-crystal magnetic particles inside a polymer matrix using fused filament fabrication. Two different magnetic materials are investigated: (i) Strontium hexaferrite inside a PA6 matrix, fill grade: 49 vol% and (ii) Samarium iron nitride inside a PA12 matrix, fill grade: 44 vol%. In the presence of the external alignment field, the strontium hexaferrite particles inside the PA6 matrix can be well aligned with a ratio of remnant magnetization to saturation magnetization in an easy axis of 0.7. No significant alignment for samarium iron nitride could be achieved. The results show the feasibility to fabricate magnets with arbitrary and locally defined easy axis using fused filament fabrication since the permanent magnets (or alternatively an electromagnet) can be mounted on a rotatable platform.

Circular polarization in atmospheric aerosols

Abstract. Recent technological advances have demonstrated the feasibility of deploying spaceborne optical detectors with full polarimetric capabilities. The measurement of all four Stokes coefficients opens significant new opportunities for atmospheric aerosol studies and applications. While considerable amounts of attention have been dedicated to sensors with sensitivity to the total intensity and linear polarization (represented by Stokes coefficients I, U, Q), there has been less attention to the additional information brought by measuring circular polarization (coefficient V). This report fills this gap in knowledge by providing an overview of aerosol sources of circular polarization in the atmosphere and discusses possible remote sensing signatures. In this paper, circularly polarized radiation that results from the interaction of incident unpolarized radiation is considered in three physical settings: optical activity originating in biogenic aerosols, alignment of non-spherical particles in the presence of electrical fields (such as dust, smoke, and volcanic ash), and aerosol multiple scattering effects. Observational and theoretical evidence of, and the settings and conditions for, non-zero aerosol circular polarization generated from incident unpolarized radiation are here gathered and discussed. In addition, novel radiative transfer simulations are shown to illustrate notable spectral and other features where circular polarization may provide additional information that is possibly independent from total intensity and linear polarization-only observations. Current techniques for the detection of aerosol composition (also referred as aerosol type) from space provide limited information. Remote identification of aerosols such as smoke, volcanic ash, and dust particles can only be accomplished with some degree of confidence for moderate to high concentrations. When the same aerosols are found at lower concentrations (but still high enough to be of importance for air quality and cloud formation), these methods often produce ambiguous results. The circular polarization of aerosols is rarely utilized, and we explore its value for improved determination aerosol composition. This study is presented as an overview with a goal to provide a new perspective on an overlooked optical property and to trigger interest in further exploration of this subject.

Acousto-Photolithography for Programmable Shape Deformation of Composite Hydrogel Sheets.

Stimuli-responsive hydrogels with programmable shapes produced by defined patterns of particles are of great interest for the fabrication of small-scale soft actuators and robots. Patterning the particles in the hydrogels during fabrication generally requires external magnetic or electric fields, thus limiting the material choice for the particles. Acoustically driven particle manipulation, however, solely depends on the acoustic impedance difference between the particles and the surrounding fluid, making it a more versatile method to spatially control particles. Here, an approach is reported by combining direct acoustic force to align photothermal particles and photolithography to spatially immobilize these alignments within a temperature-responsive poly(N-isopropylacrylamide) hydrogel to trigger shape deformation under temperature change and light exposure. The spatial distribution of particles can be tuned by the power and frequency of the acoustic waves. Specifically, changing the spacing between the particle patterns and position alters the bending curvature and direction of this composite hydrogel sheet, respectively. Moreover, the orientation (i.e., relative angle) of the particle alignments with respect to the long axis of laser-cut hydrogel strips governs the bending behaviors and the subsequent shape deformation by external stimuli. This acousto-photolithography provides a means of spatiotemporal programming of the internal heterogeneity of composite polymeric systems.

Topological Edge and Corner States Designed via Meta‐Atoms Orientation

AbstractRapid development of topological concepts in photonics unveils exotic phenomena such as unidirectional propagation of electromagnetic waves resilient to backscattering at sharp bends and disorder‐immune localization of light at stable frequencies. Recently introduced higher‐order topological insulators (HOTIs) bring in additional degrees of control over light confinement and steering. However, designs of photonic HOTIs reported so far are solely exploiting lattice geometries which are hard to reconfigure thus limiting tunability. This article reports a conceptually new mechanism to engineer topological edge and corner states including higher‐order topological phases which exploits both electric and magnetic responses of the meta‐atoms. Hybridization between these responses gives rise to the difference in the effective coupling which is controlled by the meta‐atoms mutual orientations. This feature allows to tailor photonic band topology exclusively via particle alignment and flexibly reconfigure the topological phase. Focusing on the kagome array of split‐ring resonators, the topological edge and corner states are experimentally demonstrated in the microwave domain. To highlight the generality of this proposal, the formation of higher‐order topological phase is also predicted numerically in a C6‐symmetric lattice of split‐ring resonators. These findings provide a new promising route to induce and control higher‐order topological phases and states.