Rod Aspect Ratio Research Articles

Improved hydrostatic piezoelectric property via incorporation of porous PZT ceramics into 1-3 type PZT-polymer composites: design to fabrication

PZT ceramic is widely used as sensors, especially in underwater applications like sound navigation and ranging(SONAR), due to its piezoelectric properties. However, single-phase PZT ceramics have poor hydrostatic piezoelectric properties, leading to the development of porous PZT and PZT-polymer composites. This study enhanced the hydrostatic figure of merit(HFOM) value by incorporating porous PZT into a 1-3 type composite. Finite element analysis and the ceramic injection molding(CIM) method were used for optimal design and fabrication. PZflex simulation tool derived the composite's piezoelectric properties, revealing that increased porosity reduced d33 and d31 but increased HFOM. The aspect ratio of PZT rods was selected by calculating the coupling factor. The fabricated composite had a higher HFOM value (4050(10-15Pa) at 12% porosity) than dense 1-3 type PZT-polymer composites. This study demonstrates the effectiveness of finite element analysis and CIM in designing high-performance piezoelectric composites, with potential for various future applications.

Shear flow of non-Brownian rod-sphere mixtures near jamming.

We use the discrete element method, taking particle contact and hydrodynamic lubrication into account, to unveil the shear rheology of suspensions of frictionless non-Brownian rods in the dense packing fraction regime. We find that, analogously to the random close packing volume fraction, the shear-driven jamming point of this system varies in a nonmonotonic fashion as a function of the rod aspect ratio. The latter strongly influences how the addition of rodlike particles affects the rheological response of a suspension of frictionless non-Brownian spheres to an external shear flow. At fixed values of the total (rods plus spheres) packing fraction, the viscosity of the suspension is reduced by the addition of "short"(≤2) rods but is instead increased by the addition of "long"(≥2) rods. A mechanistic interpretation is provided in terms of packing and excluded-volume arguments.

A semi-analytical wavelet finite element method for wave propagation in rectangular rods

Prior knowledge of the dispersion curves and mode shapes of guided waves provides valuable information for wave mode selection and excitation in the field of non-destructive evaluation (NDE) and structural health monitoring (SHM). They are typically computed by the matrix methods, the finite element (FE) and semi-analytical finite element (SAFE) methods. However, the former is prone to numerical instability, and the latter two are limited by the refinement level of the FE mesh. In this paper, a semi-analytical wavelet finite element (SAWFE) method is presented to characterize wave propagation in rectangular rods. The piecewise polynomial interpolation functions of the SAFE method are replaced by two-dimensional scaling functions of the B-spline wavelet on the interval (BSWI). To demonstrate the accuracy of the proposed SAWFE technique, the propagation of guided waves in an aluminium plate is studied first. Then, the propagation of guided waves in rectangular rods of arbitrary aspect ratio is investigated. The results of this work clearly show that the SAWFE method presented here has higher accuracy and efficiency than the SAFE method.

Numerical study on the gasification and shape evolution of single rod-shaped biomass char particle in a hot CO2/O2/H2O atmosphere

In the industrial systems for CO2 gasification of biomass, a large amount of feedstock is presented as rod-shaped particles at different scales. The evolution of such particles during gasification remains unclear. This work investigated the overall gasification characteristics of single rod-shaped biomass char particle in a hot CO2/O2/H2O atmosphere and the intrinsic link between shape evolution and gasification characteristics. The overall gasification characteristics of the particle are discussed, including the influence of various inlet parameters and geometric parameters. The reaction intensity on the particle surface shows significant non-uniformity, which increases with the particle Reynolds number and oxygen concentration but decreases with increasing inlet temperature. The more the particle shape resembles a rod (aspect ratio ranging from 3:2 to 3:1), the more pronounced the non-uniformity of the surface temperature becomes (increasing by over five times). The intrinsic link between particle reaction properties and shape evolution was discussed using the dynamic mesh method. The shrinkage rate at the end of the particle is 1.73 times faster than that at the middle part. The non-uniformity of the surface temperature decreases by 6 % within 5 s, indicating that as the reaction proceeds, the reaction intensity on the particle surface tends to become more uniform.

Elastic response of colloidal smectic liquid crystals: Insights from microscopic theory.

Elongated colloidal rods at sufficient packing conditions are known to form stable lamellar or smectic phases. Using a simplified volume-exclusion model, we propose a generic equationof state for hard-rod smectics that is robust against simulation results and is independent of the rod aspect ratio. We then extend our theory by exploring the elastic properties of a hard-rod smectic, including the layer compressibility (B) and bending modulus (K_{1}). By introducing weak backbone flexibility we are able to compare our predictions with experimental results on smectics of filamentous virus rods (fd) and find quantitative agreement between the smectic layer spacing, the out-of-plane fluctuation strength, as well as the smectic penetration length λ=sqrt[K_{1}/B]. We demonstrate that the layer bending modulus is dominated by director splay and depends sensitively on lamellar out-of-plane fluctuations that we account for on the single-rod level. We find that the ratio between the smectic penetration length and the lamellar spacing is about two orders of magnitude smaller than typical values reported for thermotropic smectics. We attribute this to the fact that colloidal smectics are considerably softer in terms of layer compression than their thermotropic counterparts while the cost of layer bending is of comparable magnitude.

Two-temperature activity induces liquid-crystal phases inaccessible in equilibrium.

In equilibrium hard-rod fluids, and in effective hard-rod descriptions of anisotropic soft-particle systems, the transition from the isotropic (I) phase to the nematic phase (N) is observed above the rod aspect ratio L/D=3.70 as predicted by Onsager. We examine the fate of this criterion in a molecular dynamics study of a system of soft repulsive spherocylinders rendered active by coupling half the particles to a heat bath at a higher temperature than that imposed on the other half. We show that the system phase-separates and self-organizes into various liquid-crystalline phases that are not observed in equilibrium for the respective aspect ratios. In particular, we find a nematic phase for L/D=3 and a smectic phase for L/D=2 above a critical activity.

Tailoring Li2Si2O5 rod-like particles and their simultaneously strengthening and toughening effects on lithium disilicate glass-ceramics

To achieve high performance of glass-ceramics, it is urgent to open a new path to enhance the mechanical properties. In this study, Li2Si2O5 rods were successfully synthesized by a modified two-step solid-state reaction sintering method. The rod aspect ratio could be controlled by adjusting the second stage sintering time. The evolution process of such Li2Si2O5 rods and their possible formation mechanism were put forward. For the first time, the Li2Si2O5 rods were used to strengthen and toughen the homologous Li2Si2O5 glass-ceramic in a typical quaternary Li2O-SiO2-K2O-La2O3 system, which indicates a high flexural strength and toughness of 315±24 MPa and 2.42±0.6 MPa·m1/2, respectively. In this glass-ceramic, the microstructure features a densely stagger network formed by the elongated rods and smaller Li2Si2O5 crystals in the glass matrix, contributing to the improvement of mechanical properties. The results demonstrate that Li2Si2O5 rods could be an excellent candidate for strengthening and toughening glass-ceramics.

Rigidity Percolation in Disordered 3D Rod Systems

In composite materials composed of a soft polymer matrix and rigid, high aspect-ratio particles, the composite undergoes a transition in mechanical strength when the incorporated particle phase surpasses a critical density. This phenomenon, termed rheological percolation, is well known to occur in many polymer-rod and polymer-platelet composites at a critical density that exceeds the conductivity percolation threshold (which occurs when the conducting particles form a large connected component that spans the composite). Contact percolation in rod-like composites has been routinely exploited to engineer thermal or electrical conductivity in otherwise nonconducting polymers, and the characterization of contact percolation is well established. Mechanical or rheological percolation, however, has evaded a complete theoretical explanation and predictive description. A natural hypothesis is that rheological percolation is due to a rigidity phenomenon, whereby a large rigid component of inclusions spans the composite. Here we build an algorithm to detect the rigidity percolation threshold in rod-polymer composites. We model the composites as systems of randomly distributed, soft-core (intersecting at contact) rods and study the emergence of a giant (i.e., spanning) rigid component. Building on our previous results for two-dimensional composites, we develop an approximate algorithm that identifies spanning rigid components through hierarchically identifying and compressing provably rigid motifs---equivalently, decomposing a giant rigid component into rigid assemblies of a hierarchy of successively smaller rigid components. We apply this algorithm to random monodisperse systems that are generated in Monte Carlo simulations to estimate a rigidity percolation threshold (critical density) and explore its dependence on rod aspect ratio. We show that this transition point---like its contact percolation analogue---scales inversely with the excluded volume of a rod. Moreover, this implies that the critical contact number (i.e., the number of contacts per rod at the rigidity percolation threshold) is constant for aspect ratios above some relatively low value and is lower than the prediction from Maxwell's isostatic condition.

Monte Carlo study of plastic rod scintillators for use in industrial computed tomography

Industrial gamma-ray computed tomography systems have found different applications and have become an important tool for non-destructive testing. In this work, high aspect ratio rod plastic scintillators were assessed for use in this type of tomography system. All analyses were performed using Monte Carlo simulation by geant4 toolkit. Validation of the results was done using a 50 cm rod plastic scintillator with a diameter of 5 cm. The results showed that the rod plastic scintillators can be employed in industrial tomography systems for scanning large objects. The spatial resolution of the detection system was estimated more than 1 cm. Finally, the simulated parameters of the selected rod plastic scintillator were compared with an identical NaI(Tl) rod scintillator to find a better understanding about its performance.

Growth twinning and morphology of Al45Cr7 and Al13Fe4

Twinned crystal growth is studied in primary Al45Cr7 and Al13Fe4 intermetallic compounds (IMCs) to explore how different twin types and twin variants affect the growth morphology during solidification. In both IMCs, the number of twin variants increased as the cooling rate increased and, by ~ 5 K/s, both IMCs formed cyclic twins with combined icosahedral (Al45Cr7) or decagonal (Al13Fe4) pseudosymmetry. The growth morphology depended on which twin variants were present. When all twin domains shared a common direction that was a rod growth direction in single crystals, twinning did not prevent crystals from growing as rods. This was the case for both IMCs at slow cooling rate and Al13Fe4 at all cooling rates. Cyclic twinning of Al13Fe4 generated many re-entrant corners but resulted in only a modest reduction in rod aspect ratio. In contrast, when twin domains in Al45Cr7 had common directions along multiple pseudo-i(2) axes, crystal growth transitioned from rod-like to a near-equiaxed morphology.

Multiphase Coexistences in Rod-Polymer Mixtures.

Using recently derived analytical equations of state for hard rod dispersions, we predict the phase behavior of athermal rod–polymer mixtures with free volume theory. The rods are modeled as hard spherocylinders, while the nonadsorbing polymer chains are described as penetrable hard spheres. It is demonstrated that all of the different types of phase states that are stable for pure colloidal rod dispersions can coexist with any combination of these phases if polymers are added, depending on the concentrations, rod aspect ratio, and polymer–rod size ratio. This includes novel two-, three-, and four-phase coexistences and isostructural coexistences between dilute and concentrated phases of the same kind, even for the more ordered (liquid) crystal phases. This work provides insight into the conditions at which particular multiphase coexistences are expected for well-defined model colloidal rod–polymer mixtures. We provide a quantitative map detailing the various types of isostructural coexistences, which confirms an early qualitative hypothesis by Bolhuis et al. (J. Chem. Phys.107, 19971551).

Sheathless Separation of Cyanobacterial Anabaena by Shape Using Viscoelastic Microfluidics.

Cyanobacteria have a wide range of impact on natural ecosystems, and have been recognized as potentially rich sources of pharmacological and structurally interesting secondary metabolites. To better understand the basic molecular processes and mechanisms that influence and regulate the growth (like length) of cyanobacteria, or connections between environment, genotype, and phenotype, it would be essential to separate shape-synchronized cyanobacterial cell populations with relatively uniform length and size. This work proposes a novel and efficient method to separate cyanobacterial Anabaena by shape (rod aspect ratio) using viscoelastic microfluidics in a straight channel with expansion-contraction cavity arrays (ECCA channel). The biocompatible viscoelastic solutions with dissolved polymer would induce a combined effect of inertial lift force, elastic force, and secondary drag force for Anabaena flowing in it. Therefore, Anabaena with different lengths reach different lateral equilibrium positions and flow out from different outlets. Factors including flow rate, fluid viscoelasticity, channel structure, and length on the shape-based cell separation were studied systematically. This work, for the first time, demonstrates continuous and sheathless shape-based separation of cyanobacteria using viscoelastic microfluidics. Moreover, its ability to manipulate objects with different morphologies and with a size of >100 μm will extend the capability of microfluidics to a completely new field that has never been reached and would be attractive across a range of new applications.

Are Langmuir Trough Studies Useful? Unexpected Emulsification Behavior Using Colloidal Rods.

While studies carried out in a Langmuir trough have rigorously demonstrated that, at high surface pressure, ellipsoidal particles do flip and spherocylinders (rods) can flip, much less is known about the practical situation on the surface of a droplet or bubble. We present emulsification studies using colloidal rods and find that the droplets are bridged by the rods independent of shear rate and particle concentration and are only weakly dependent on the pH of the continuous phase. In a trough, it is the low aspect ratio rods which flip and the high aspect ratio rods which form bilayers; on the surface of a droplet we found that the high aspect ratio rods always bridge whereas the shorter rods show random bridging behavior. Hence, the behavior of anisotropic particles "in action" is essentially opposite to expectations from trough studies.

A reduced-order model based on finite element method for fast prediction of thermal performance of lattice structures

Lattice structures, emerging with additive manufacturing technology, have broad application prospects in industry, and desirable thermal and mechanical properties of which can be obtained by changing the internal cells and their array mode. However, the computational cost for the design and analysis of a lattice structure is usually extremely high due to the structural complexity. For fast prediction of thermal performance of lattice structures, a reduced-order model was developed, in which the complex lattice structure is simplified into a three-dimensional rod system and the heat conduction, convection, and radiation are modeled in a reduced second-order way based on the finite element principle. The convergence and accuracy was examined, and the model validation was done by comparing with the corresponding full model. The results showed that the calculation error of the reduced-order model decreases as the rod aspect ratio increases and the computational efficiency is improved by more than 1000 times. The reduced-order model was then applied to evaluate the thermal insulation and thermal dissipation performance of seven kinds of lattice cells, and their characteristics of the thermal performance were found and compared. We finally gave a better designed cell, which shows the best thermal insulation and dissipation performance simultaneously.

Au-Cu@PANI Alloy Core Shells for Aerobic Fibrin Degradation under Visible Light Exposure.

Fibrin plays a critical role in wound healing and hemostasis, yet it is also the main case of cardiovascular diseases and thrombosis. Here, we show the unique design of Au-Cu@PANI alloy core-shell rods for fibrin clot degradation. Microscopic (transmission electron microscopy (TEM), scanning transmission electron microscopy-energy-dispersive X-ray (STEM-EDX)) and structural characterizations (powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)) of the Au-Cu@PANI hybrid material reveal the formation of Au-Cu heterogeneous alloy core rods (aspect ratio = 3.7) with thin Cu2O and PANI shells that create a positive surface charge (ζ-potential = +22 mV). This architecture is supported by the survey XPS spectrum showing the presence of Cu 2p, N 1s, and C 1s features with binding energies of 934.8, 399.7, and 284.8 eV, respectively. Upon photolysis (λ ≥ 495 or 590 nm), these hybrid composite nanorods provide sufficient excited-state redox potential to generate reactive oxygen species (ROS) for degradation of model fibrin clots within 5-7 h. Detailed scanning electron microscopy (SEM) analysis of the fibrin network shows significant morphology modification including formation of large voids and strand termini, indicating degradation of fibrin protofibril by Au-Cu@PANI. The dye 1,3-diphenylisobenzofuran (DPBF) used to detect the presence of 1O2 shows a 27% bleaching of the absorption at λ = 418 nm within 75 min of irradiation of an aqueous Au-Cu@PANI solution in air. Moreover, electron paramagnetic resonance (EPR) spin-trapping experiments reveal a hyperfine-coupled triplet signature at room temperature with intensities 1:1:1: and g-value = 2.0057, characteristic of the reaction between the spin probe 4-Oxo-TEMP and 1O2 during irradiation. Controlled 1O2 scavenging experiments by NaN3 show 82% reduction in the spin-trapped EPR signal area. Both DPBF bleaching and EPR spin trapping indicate that in situ generated 1O2 is responsible for fibrin strand scission. This unique nanomaterial function via use of ubiquitous oxygen as a reagent could open creative avenues for future in vivo biomedical applications to treat fibrin clot diseases.

Nanoparticle formation through dewetting of a solid-state thin film on a substrate: A phase-field study

Abstract During dewetting of a solid-state thin film on a substrate, the film tends to agglomerate into islands to reduce its total interfacial energy, which can be utilized as an economical pattern formation technique. In this work, we are using a three-dimensional phase-field model to understand the conditions and the mechanisms of island formation through pinch-off during dewetting of a finite cylindrical film on a substrate. It is observed that the pinch-off is mostly affected by the wetting angle, which is a function of interfacial energies between substrate, film, and vapor. The role of the aspect ratio of the cylindrical rod on island (nanoparticle) formation is also analysed.

Self-assembly of single-crystal ZnO nanorod arrays on flexible activated carbon fibers substrates and the superior photocatalytic degradation activity

The synthesis of one-dimensional nanocrystals on flexible substrates has attracted a great attention in the last decade. We here report an integrated approach using a sequential sol-gel and hydrothermal synthesis method to successfully assemble well-aligned single-crystalline wurtzite ZnO nanorod arrays (ZnO NRAs) on activated carbon fibers (ACFs). The ZnO NRAs, with high rod surface area (up to 20 m2 g−1), high aspect ratio (rod length/rod diameter, ca. 20:1) and high defect level (indicated by an extremely sharp blue emission, strong green and yellow emissions), were shown to grow nearly perpendicularly on the ACFs surface. The pre-coating of ZnO seed layers on ACFs surface during sol-gel synthesis is vital for the growth of the ordered ZnO nanorod arrays. The structural and optical properties of ZnO NRAs/ACFs can be adjusted by tuning the synthesis parameters for sol-gel and hydrothermal steps. As compared to the ZnO NRAs grown on the stiff substrates (e.g., silicon wafer, fluorine-doped tin oxide glass, GaN and metal sheets), ZnO NRAs grown on ACFs have very high surface area and intensive blue, green and yellow emissions. The novel ZnO NRAs/ACFs show excellent photocatalytic degradation of methylene blue and robust recyclability as compared to the individual ZnO nano particles (powder, NRs and NRAs).

Planar Orientation Control and Torque Maximization Using a Swarm With Global Inputs

This paper studies the torque applied by a large number of particles on a long aspect-ratio rod. The particles are all pushed in the same direction by a global signal. We calculate the force and torque generated by three canonical position distributions of a swarm: uniform, triangular, and normal. The model shows that for a pivoted rod the uniform distribution produces the maximum torque for small swarm standard deviations, but the normal distribution maximizes torque for large standard deviations. In the simulation, we use these results to design proportional-derivative controllers to orient rigid objects. We conclude showing the experiments with up to 97 hardware robots to evaluate our theory in practice.

Ligand Surface Density Decreases with Quantum Rod Aspect Ratio

The relationship between phosphonic acid (PA) binding strength, surface coverage, and quantum rod or dot aspect ratio was studied. Seven nanocrystals with an aspect ratio (l/w) between 1.0 and 11.7, including five CdSe with l/w between 1.0 and 5.2 and two CdSe/CdS with dot-in-rod and rod-in-rod microstructures with l/w between 7.5 and 11.7, were synthesized. The nature of phosphonic acid binding was studied in situ using one-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy as well as two-dimensional diffusion ordered spectroscopy (DOSY) and relaxation ordered spectroscopy (ROSY). The DOSY results were used to separate strongly binding phosphonic acid signatures from weakly binding ones, thus allowing for estimates of ligand densities (LDs) to be calculated, which showed a significant drop from LD = 2.21 nm–2 for spherical CdSe with l/w = 1.0 to LD = 0.23 nm–2 for CdSe/CdS with l/w = 11.7. Interestingly, intermediate l/w = 1.7 showed a higher LD of 4.81 nm–2. The results suggest a wrapping or relatively flat binding by phosphonic acids on the sides of the rods, leading to decent surface coverage for low aspect ratios but lower LD for more elongated rods. This model was further confirmed using ROSY, which revealed similar relaxation times (T1) for each proton of the phosphonic acids on the rods, indicating similar ligand–quantum rod (QR) interface.

Microstructure of Rod-Based Capillary Suspensions with Different Rod Aspect Ratios under Quiescent and Shear Flow

A particle-assembled microstructure in ternary capillary suspensions consisting of polyisobutylene (PIB) as the matrix phase, poly(ethylene oxide) (PEO) as the minor fluid phase, and silica (SiO2) particles with different aspect ratios (ARs) is probed by an in situ optical-shear technique, scanning electronic microscopy, and confocal laser scanning microscopy as well as rheometry. It is found that the capillary bridging force brought by the presence of the PEO wetting layer between particles can be influenced by the AR of particles and shear rate, which all play decisive roles in determining the microstructure and rheological properties of suspensions. Moreover, two novel aggregation modes of rods and an interesting spatiotemporal organization phenomenon of particle aggregates (vorticity-aligned particle bands) are found under shear flow.