Rod-like Particles Research Articles

Drag, lift and torque correlations for axi-symmetric rod-like non-spherical particles in locally linear shear flows

This paper derives new correlations to predict the drag, lift and torque coefficients of axi-symmetric non-spherical rod-like particles for several fluid flow regimes and velocity profiles. The fluid velocity profiles considered are locally uniform flow and locally linear shear flow. The novel correlations for the drag, lift and torque coefficients depend on the particle Reynolds number Rep, the orientation of the particle with respect to the main fluid direction θ, the aspect ratio of the rod-like particle α, and the dimensionless local shear rate G̃. The effect of the linear shear flow on the hydrodynamic forces is modeled as an additional component for the resultant of forces acting on a particle in a locally uniform flow, hence the independent expressions for the drag, lift and torque coefficients of axi-symmetric particles in a locally uniform flow are also provided in this work. The data provided to fit the coefficient in the new correlation are generated using available analytical expressions in the viscous regime, and performing direct numerical simulations (DNS) of the flow past the axi-symmetric particles at finite particle Reynolds number. The DNS are performed using the direct-forcing immersed boundary method. The coefficients in the proposed drag, lift and torque correlations are determined with a high degree of accuracy, where the mean error in the prediction lies below 2% for the locally uniform flow correlations, and bwlow 1.67%, 5.35%, 6.78% for the correlation accounting for the change in the drag, lift, and torque coefficients in case of a linear shear flow, respectively. The proposed correlations for the drag, lift and torque coefficients can be used in large-scale simulations performed in the Eulerian-Lagrangian framework with locally uniform and non-uniform flows.

Conditions under which a natural iterative method for calculating the orientation distribution of rodlike particles decreases the free energy at each step.

It is shown that under certain conditions the iterative method suggested by the calculus of variations for calculating a cylindrically symmetric orientation distribution function (ODF) for rodlike particles strictly decreases the free energy at each full step. This monotonic behavior has strong implications for convergence of the sequence, or a subsequence, of the calculated ODFs. The result is valid not only for the reference system of hard core particles with indistinguishable ends, but also for free energy functions of similar type. The effect of an applied field is also permitted. Since the behavior of the iteration is intrinsic to the general form of the free energy function it applies to rod mixtures and may extend to a wider class of free energy functions. Outside the conditions that guarantee a monotonically decreasing free energy, we find that the iteration can fail to converge.

Structural characterisation of α-synuclein-membrane interactions and the resulting aggregation using small angle scattering.

The presence of amyloid fibrils is a hallmark of several neurodegenerative diseases. Some amyloidogenic proteins, such as α-synuclein and amyloid β, interact with lipids, and this interaction can strongly favour the formation of amyloid fibrils. In particular the primary nucleation step, i.e. the de novo formation of amyloid fibrils, has been shown to be accelerated by lipids. However, the exact mechanism of this acceleration is still mostly unclear. Here we use a range of scattering methods, such as dynamic light scattering (DLS) and small angle X-ray and neutron scattering (SAXS and SANS) to obtain structural information on the binding of α-synuclein to model membranes formed from negatively charged lipids and their co-assembly into amyloid fibrils. We find that the model membranes take an active role in the reaction. The binding of α synuclein to the model membranes immediately induces a major structural change in the lipid assembly, which leads to a break-up into small and mostly disc- or rod-like lipid-protein particles. This transition can be reversed by temperature changes or proteolytic protein removal. Incubation of the small lipid-α-synuclein particles for several hours, however, leads to amyloid fibril formation, whereby the lipids are incorporated into the amyloid fibrils.

Structural and opto-electrical properties of Y2O3 nanopowders synthesized by co-precipitation method

The synthesis-dependent structural-optical characteristics of nanomaterials have induced the critical optimization of parameters for nanoparticle synthesis. Considering the potential applications of yttria (Y2O3) in high-temperature IR windows and electro-optic devices, the present study describes the preparation of yttria nanopowders (YNPs) through co-precipitation method. Some special morphological and opto-electrical properties have been observed with a change in the precipitating agent concentration (R = NH5CO3/Y3+ = 1.5–5.5) without using any surfactant. Rietveld refinement confirmed the body-centered cubic (Ia-3 space group) structure of YNPs. Surface functionalities have been determined by Fourier transform infrared (FTIR) spectroscopy. Electron microscopy results confirmed the formation of agglomerated YNPs with R-dependent morphological modifications from flake-like shape to pseudo-spherical and rod-like particles. UV–visible and fluorescence (FL) spectroscopy confirmed the R-dependent optical absorption and emission (indigo, blue and green) characteristics. The dielectric measurement also confirmed the R-dependent variation in the dielectric constant values in the lower frequency range.

Structural properties and electrochemical performances of mesoporous carbon towards enhanced lithium-ion storage

This study analyzes the structural characteristics of mesoporous carbon (CMK-3) and how they affect the specific capacity of Li-ion batteries (LIBs). To achieve this, CMK-3 is synthesized with and without the addition of oxalic acid as a catalyst to polymerize furfuryl alcohol (carbon precursor) in the template-assisted synthesis process using mesoporous silica. CMK-3 (without oxalic acid) and CMK-3_O (with oxalic acid) exhibit rod-like particles with cylindrical pores, showing high specific surface area (SSA) of 998 and 1067 ​m2 ​g−1 and oxygen-to-carbon ratios of 0.23 and 0.43, respectively. At 178 ​mA ​g−1, the electrodes demonstrate specific capacities of 993 ​mA ​h ​g−1 (CMK-3) and 520 ​mA ​h ​g−1 (CMK-3_O). According to the cyclic voltammetry technique, the non-diffusion-controlled process (approximately 55 ​%) significantly contributes to the total charge storage in CMK-3. Although electrodes (CMK-3 and CMK-3_O) have similar SSA, this study highlights the significance of the disordered and defective structure in achieving a higher specific capacity from the same material without any changes in morphology, particle size, or synthesis route. Consequently, this work emphasizes the necessity of considering the structural properties of porous carbon electrodes when developing high-performance batteries for electric vehicles, where specific capacity and cyclic stability are crucial.

Effects of hydrolysis conditions on the morphology of cellulose II nanocrystals (CNC-II) derived from mercerized microcrystalline cellulose

The properties of cellulose nanocrystals with allomorph II (CNC-II) vary with the sources and the treatments received. In this work, the influences of hydrolysis time, temperature, and the applied acid concentration on the crystal size of CNC-II were investigated by the surface response experimental design. The results showed that temperature was the most significant factor affecting the crystal size of CNC-II during hydrolysis from mercerized cellulose. Then the morphology and colloidal properties of CNC-II were revealed by dynamic laser scattering (DLS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc. XRD results indicated that CNC-II had slightly lower crystallinity (80.89 % vs 82.7 %) and larger crystallite size (5.21 vs. 5.13 nm) than CNC-I. TEM and AFM results showed that the morphology of CNC-II were disc-like and rod-like particles, with an average diameter of 14.6 ± 4.7 nm (TEM) and a thickness of 4– 8 nm (AFM). TG and XPS revealed the reduced thermal stability was due to the introduced sulfate groups in CNC-II during hydrolysis. This investigation has addressed the features of CNC-II derived from mercerized cellulose, and it would be promising in fabricating advanced materials.

Complex motion of steerable vesicular robots filled with active colloidal rods

While the collective motion of active particles has been studied extensively, effective strategies to navigate particle swarms without external guidance remain elusive. We introduce a method to control the trajectories of two-dimensional swarms of active rod-like particles by confining the particles to rigid bounding membranes (vesicles) with non-uniform curvature. We show that the propelling agents spontaneously form clusters at the membrane wall and collectively propel the vesicle, turning it into an active superstructure. To further guide the motion of the superstructure, we add discontinuous features to the rigid membrane boundary in the form of a kinked tip, which acts as a steering component to direct the motion of the vesicle. We report that the system’s geometrical and material properties, such as the aspect ratio and Péclet number of the active rods as well as the kink angle and flexibility of the membrane, determine the stacking of active particles close to the kinked confinement and induce a diverse set of dynamical behaviors of the superstructure, including linear and circular motion both in the direction of, and opposite to, the kink. From a systematic study of these various behaviors, we design vesicles with switchable and reversible locomotions by tuning the confinement parameters. The observed phenomena suggest a promising mechanism for particle transportation and could be used as a basic element to navigate active matter through complex and tortuous environments.

Two-dimensional strain rate imaging study using a polarization camera and birefringent aqueous cellulose nanocrystal suspensions

The birefringence response of aqueous cellulose nanocrystal (CNC) suspensions in a two-dimensional laminar flow is measured and studied. The suspensions have CNC concentrations of 1.0 wt% (weight percentage) and 1.2 wt%. Cellulose nanocrystals are optically anisotropic rod-like particles that align when subjected to local velocity gradients, whereas at rest, they remain randomly orientated by Brownian motion. The alignment causes birefringence, a phenomenon also known as flow-induced birefringence. We study the flow through an additively manufactured flow channel and measure the amount of birefringence as well as the position of the refractive index axes by using polarizers and a polarization camera. With the help of reference data published in a previous study (Lane, Rode, et al., 2022a), strain rates are derived from the birefringence measurements and compared with numerical simulations. Two flow situations are studied, a plane Poiseuille flow and the flow around a cosine-shaped constriction. The experimentally derived shear rates for the plane Poiseuille flow are consistent with theoretical and computational results. The derived strain rates for the flow around the cosine-shaped constriction show an unexpected asymmetric profile, with the strain rates in the contraction zone being larger than in the expansion zone. The averaged orientation of the CNCs in the flow is linked to the position of the refractive index axes. In the contraction zone, the CNCs tend to align parallel to the flow, whereas in the expansion zone, the CNCs tend to align perpendicular to the flow. The results of this study are discussed in the context of previous, similar studies. The asymmetric strain rate profile around the cosine-shaped constriction is thought to originate from history effects, and the alignment of the CNCs is influenced by extensional rates.

Effects of annealing treatment on microstructure and mechanical properties of laser melting-deposited VCoNi medium-entropy alloy

Additive manufacturing (AM) is a promising approach to producing high- or medium-entropy alloys (HEAs or MEAs) with excellent properties. However, some undesirable microstructural defects and unstable precipitated phases were formed owing to the repeated heating and cooling steps and the rapid solidification nature of the AM process. Annealing treatment after AM fabrication is often beneficial for adjusting the comprehensive mechanical properties and stabilizing the microstructures. In this study, a VCoNi MEA single wall sample was fabricated successfully via laser melting deposition (LMD), and the effects of post-annealing treatments on the microstructures and mechanical properties were explored. The grain size and σ-phase particle size increase and the σ-phase particles undergo fragmentation, spheroidization, and coarsening during annealing. As the annealing time increases, the tensile strain increases, but the tensile strength decreases. An excellent combination of strength and ductility can be obtained after annealing for 1.5 h (The yield strength, ultimate tensile strength, and tensile strain are 741.2 MPa, 1287.8 MPa, and 30.5 %, respectively). HDI hardening is the most important strengthening mechanism in this work. The decrease in tensile stress after the annealing treatment is mainly attributed to the decrease of heterogeneity of microstructure, and the increase in tensile strain after the annealing treatment is mainly attributed to the decrease of the pores and the spheroidization of the rod-like σ-phase particles. This work provides practical insight into adjusting the microstructure and comprehensive mechanical properties of HEAs and MEAs for AM.

Preparation and Structure of Zinc–Calcium Hydroxyapatite Solid Solution Particles and Their Ultraviolet Absorptive Ability

The calcium ions (Ca2+) of calcium hydroxyapatite (CaHap) were substituted with zinc ions (Zn2+), and zinc–calcium hydroxyapatite solid solution (ZnCaHap) particles were prepared via a precipitation method. The structure of the various obtained particles was investigated via powder X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectrometry. The ultraviolet (UV) absorption ability of the particles was also investigated using UV–Vis spectroscopy. The morphology of the CaHap comprised fine ellipsoidal particles, and long rod-like particles and large plate-like particles were mixed with the fine particles at higher Zn2+ contents in the particles. Pure ZnCaHap particles were obtained from the starting solution at less than Zn/(Zn + Ca) ([XZn]) of 0.25. Another crystal phase was mixed with the ZnCaHap phase at [XZn] ≥ 0.25. The crystallinity and lattice parameters a and c of the particles decreased with an increase in [XZn] from 0 to 0.10. The UV absorptive ability of the particles first increased and then decreased with increasing Zn2+ content and showed a maximum at [XZn] = 0.30.

Visible-light responsive BiVO4 nanocompositions: Enhanced photocatalytic, electrical and optical performance through Ni and Ni/Co doping

The pronounced light sensitivity of BiVO4 has garnered significant attention, establishing it as a visible light-responsive photocatalyst. This study was focused on enhancing the optical, dielectric constant properties, and photocatalytic activity of BiVO4 compositions. By employing a modified combustion method, pure BiVO4, Ni-mono-doped (BiNi0.02V0.98VO4), and Ni/Co-bi-doped (BiCo0.02Ni0.02V0.96VO4) were synthesized. X-ray diffraction (XRD) analysis validated the formation of a monoclinic BiVO4 phase. The incorporation of Ni2+ and Co2+ ions into the BiVO4 lattice was supported by variations in the lattice parameters, volume expansion and increased average crystallite size. Morphological investigation via scanning electron microscopy (SEM-EDAX) confirmed the purity of the synthesized nanocompositions and unveiled distinctive rod-like and needle-like particle shapes in BiNi0.02Co0.02V0.96VO4, with an aspect ratio of 0.07–0.1, indicating potential benefits for efficient charge separation in photocatalysis. Optical examination highlighted redshifts in band gap energy (2.36 eV) due to both Ni and (Co, Ni) co-doping, leading to direct band gaps of 2.34 eV and 2.32 eV, respectively. High refractive index values exceeding 2.5, conducive to optical applications, were observed across all samples. Through Ni and Ni/Co doping process, a notable enhancement in conductivity emerged, particularly within the low-frequency domain. The co-doping of Ni and Co demonstrated elevated relative permittivity (εʹ) values exclusively within the low-frequency span, up to 100 Hz. In contrast, the Ni-mono-doping interestingly disclosed an enhancement in (εʹ) across all frequency ranges. Photocatalytic results demonstrated heightened degradation activity in doped samples, with the BiNi0.02Co0.02V0.96VO4, sample exhibiting the highest rate, achieving 88 % degradation efficiency in 180 min. This exceptional performance can be attributed to its visible-light-responsive band gap, increased electron-hole trapping sites, and distinct morphology.

Lateral-Concentration Inhomogeneities in Flows of Suspensions of Rod-like Particles: The Approach of the Theory of Anisotropic Micropolar Fluid

Lateral-Concentration Inhomogeneities in Flows of Suspensions of Rod-like Particles: The Approach of the Theory of Anisotropic Micropolar Fluid

Microstructure evolution and mechanical properties of bioinspired web-liked (TiB + TiC + Ti3Si)/TC4 composites

In this study, bioinspired web-liked multiphase (TiB + TiC+Ti3Si)/TC4 composites were successfully constructed by employing the boron-modified polysilazane polymer as a source of B/C/Si. The bioinspired architecture consisted of long TiB nanowires with ultra-high aspect ratios (up to 48.2) acting as ‘web’, and hybrid spheroidal TiC and rod-like Ti3Si particles serving as ‘nodes’. The multiphase reinforcements were grown through the unique SLS (solid-liquid-solid) mechanism based on multiple liquid phases at the core-shell TC4@BmPSZ interface. The enhanced strength of bioinspired web-liked composites was attributed to the synergistic load transfer of hybrid reinforcements. Notably, the flexural strength reached up to 1863 MPa with a high crack-initiation toughness (KIc) of 17.8 MPa·m1/2. The insights gained from this study provided a promising design approach for developing of high-performance TMCs with high reinforcement content, utilizing polymer instead of traditional ceramic powder.

Hydrothermal synthesis of Mn2+- and Cu2+-doped calcium hydroxyapatite: morphological features and importance of EPR insights

This study aims to explore the effects of various hydroxyapatite (HA) doping techniques in depth. For this purpose, two ions with comparable sizes, namely Mn2+ and Cu2+, were selected based on their suitability as dopants for HA in biomedical applications. Moreover, their paramagnetic properties enable sample characterization through electron paramagnetic resonance (EPR) spectroscopy. Two different approaches were employed: (I) ion-substituted α-TCP was used as starting material; (II) foreign ions presented in the solution during the transformation of undoped α-TCP to HA. The foreign ions influenced the hydrolysis process of α-TCP, altering the phase purity and morphology of the products. Doped α-TCP showed a weaker effect, while adding ions to the synthesis solution had substantial impact. Mn-doped α-TCP transformed into plate-like HA particles while Mn2+ ions present in the solution led to the formation of both plate- and rod-shaped particles. In contrast, Cu2+ ions induced the formation of rod-like particles independently of the doping process. Plate-like particles demonstrated higher Brunauer–Emmet–Teller surface area (SBET) than rod-like HA. Each sample exhibited a combination of mesopores and macropores, with mesopores in the range of 15–17 Å being dominant. EPR investigations revealed that Mn2+ and Cu2+ are excellent paramagnetic probes to monitor synthesis reactions of HA and determine the localisation of foreign ions in the material.

Geometrical exponents of contour loops on ballistic deposition model with power-law distributed noise

In this paper, we study geometrical properties of contour loops to characterize the morphology of the porous ballistic deposition model with power-law distributed noise. In this model, rod-like particles with variable lengths instead of homogeneous particles are deposited, the length of each rod, l, is determined by a power-law distribution, P(l)∼l−(μ+1), and μ indicates the power-law strength exponent. The accumulation of rods with different lengths leads to a porous structure. The porous structure is converted into contour loops by using the Hoshen–Kopelman algorithm and the complexity and fractal features of the loops are investigated. On the other hand, the distributions of loops indicating the porosity distribution of the growth rough surfaces are investigated. The fractal dimension of the contour set, d, the fractal dimension of each loop, Df, cumulative distributions exponent of areas, ξ, and the perimeter distribution exponent, τ, are calculated for the investigated porous structures. Our results show that enhancement of μ exponent and appearance of the Gaussian ballistic deposition model leads to reduction of structure porosity and enhancement of contour loops area and perimeter. The fractal dimension of the contour set, and the fractal dimension of each loop increases by enhancement of μ exponent. Distributions of loops and geometrical exponents of contour loops in different μ exponent are determined. The results indicate that the hyperscaling relation and Zipf’s law hold for μ≥μc=3 which power-law distributed noise approaches to Gaussian one.

Influence of pH adjustment and surfactant addition on the particle morphology and photocatalytic performance of hydrothermally synthesized BiVO4

Under hydrothermal conditions, 9 bismuth vanadate (BiVO4) samples with different particle morphologies (BVO-1 to BVO-9) were prepared through pH adjustment and/or surfactant addition. BVO-6 presented a new hollow-cuboid-like particle morphology for BiVO4, while BVO-5, which exhibited a rod-like particle morphology, was the best BiVO4 sample for the photocatalytic degradation of methylene blue (MB). The pathways and mechanism for MB degradation by BVO-5 were studied by density functional theory (DFT) and liquid chromatography–mass spectrometry (LC-MS) analyses. In addition to MB, 14 other organic pollutants were degradable by BVO-5, indicating the broad applications of the BiVO4 photocatalyst in the photodegradation of pollutants.

Janus helices: From fully attractive to hard helices.

The phase diagram of hard helices differs from its hard rods counterpart by the presence of chiral "screw" phases stemming from the characteristic helical shape, in addition to the conventional liquid crystal phases also found for rod-like particles. Using extensive Monte Carlo and Molecular Dynamics simulations, we study the effect of the addition of a short-range attractive tail representing solvent-induced interactions to a fraction of the sites forming the hard helices, ranging from a single-site attraction to fully attractive helices for a specific helical shape. Different temperature regimes exist for different fractions of the attractive sites, as assessed in terms of the relative Boyle temperatures, that are found to be rather insensitive to the specific shape of the helical particle. The temperature range probed by the present study is well above the corresponding Boyle temperatures, with the phase behaviour still mainly entropically dominated and with the existence and location of the various liquid crystal phases only marginally affected. The pressure in the equation of state is found to decrease upon increasing the fraction of attractive beads and/or on lowering the temperature at fixed volume fraction, as expected on physical grounds. All screw phases are found to be stable within the considered range of temperatures with the smectic phase becoming more stable on lowering the temperature. By contrast, the location of the transition lines do not display a simple dependence on the fraction of attractive beads in the considered range of temperatures.

Optimal motility strategies for self-propelled agents to explore porous media.

Microrobots for, e.g., biomedical applications, need to be equipped with motility strategies that enable them to navigate through complex environments. Inspired by biological microorganisms we re-create motility patterns such as run-and-reverse, run-and-tumble, or run-reverse-flick applied to active rodlike particles in silico. We investigate their capability to efficiently explore disordered porous environments with various porosities and mean pore sizes ranging down to the scale of the active particle. By calculating the effective diffusivity for the different patterns, we can predict the optimal one for each porous sample geometry. We find that providing the agent with very basic sensing and decision-making capabilities yields a motility pattern outperforming the biologically inspired patterns for all investigated porous samples.

Ordering properties of anisotropic hard bodies in one-dimensional channels.

The phase behavior and structural properties of hard anisotropic particles (prisms and dumbbells) are examined in one-dimensional channels using the Parsons-Lee (PL) theory, and the transfer-matrix and neighbor-distribution methods. The particles are allowed to move freely along the channel, while their orientations are constrained such that one particle can occupy only two or three different lengths along the channel. In this confinement setting, hard prisms behave as an additive mixture, while hard dumbbells behave as a non-additive one. We prove that all methods provide exact results for the phase properties of hard prisms, while only the neighbor-distribution and transfer-matrix methods are exact for hard dumbbells. This shows that non-additive effects are incorrectly included into the PL theory, which is a successful theory of the isotropic-nematic phase transition of rod-like particles in higher dimensions. In the one-dimensional channel, the orientational ordering develops continuously with increasing density, i.e., the system is isotropic only at zero density, while it becomes perfectly ordered at the close-packing density. We show that there is no orientational correlation in the hard prism system, while the hard dumbbells are orientationally correlated with diverging correlation length at close packing. On the other hand, positional correlations are present for all the systems, the associated correlation length diverging at close packing.

Room-Temperature Nitric Oxide Gas Sensors Based on NiO/SnO2 Heterostructures.

Nitric oxide (NO) is a very well-known indoor pollutant, and high concentrations of it in the atmosphere lead to acid rain. Thus, there is great demand for NO sensors that have the ability to work at room temperature. In this work, NiO/SnO2 heterostructures have been prepared via the polyol process and were tested against different concentrations of NO gas at room temperature. The structural and morphological characteristics of the heterostructures were examined using X-ray diffraction and scanning electron microscopy, respectively, while the ratio of NiO to SnO2 was determined through the use of energy-dispersive spectrometry. The effects of both pH and thermal annealing on the morphological, structural and gas-sensing properties of the heterostructure were investigated. It was found that the morphology of the heterostructures consisted of rod-like particles with different sizes, depending on the temperature of thermal annealing. Moreover, NiO/SnO2 heterostructures synthesized with pH = 8 and annealed at 900 °C showed a response of 1.8% towards 2.5 ppm NO at room temperature. The effects of humidity as well as of stability on the gas sensing performance were also investigated.