Rigid Particles Research Articles

Fast inverse elastic scattering of multiple particles in three dimensions* *The first author was partially supported by the Funds for Creative Research Groups of NSFC (No. 11621101), NSFC Grants 11871427 and U21A20425.

Many applications require recovering the geometric information of multiple elastic particles based on the scattering information. In this paper, we consider the inverse time-harmonic elastic scattering of multiple rigid particles in three dimensions. We measure the far field information and apply the time reversal method to recover the unknown elastic particles. Two regimes are considered depending on the size and distance among particles. First, an asymptotic analysis for the imaging of small and distant particles is given based on the scattering property of a single particle, which can be used for selective focusing. Second, when particles are not small but well-separated, a fast algorithm, based on the combination of multiple scattering theory and fast multipole method, is proposed to efficiently simulate the forward multiple scattering problem and applied to the inverse elastic scattering. Numerical experiments demonstrate the proposed method can effectively recover the locations and shapes of multiple unknown particles.

Settling of heavy cylindrical particles in granular beds

The way a rigid cylindrical particle falls through a viscous Newtonian liquid into a loosely packed granular bed of smaller and lighter particles has been studied numerically. This solid-liquid flow system has been solved with the lattice-Boltzmann method combined with an immersed boundary method for explicitly imposing no-slip at the particle surfaces. We study the effect of the orientation of the cylinder (vertical and horizontal), its settling speed (the Reynolds numbers at impact is of the order of 100), and its density (relative to liquid and bed density) on the depth of penetration into the granular bed. The simulation results are particularly sensitive to the friction between particles as parameterized through friction coefficients (varied in the range 0.15 – 0.50). The results have practical relevance for particles getting immobilized – or even buried – in granular beds. More importantly, the simulation cases have been designed such as to allow for straightforward experimentation the results of which would be valuable for further numerical model development.

Experiments and simulations of settling cylinders over a wide range of Archimedes numbers

AbstractQuantitative visualization experiments and particle‐resolved simulations of rigid cylindrical particles settling in a Newtonian liquid have been conducted. By varying the viscosity of the liquid—a glycerol‐water mixture—as well as the density of the cylinders, we were able to cover an Archimedes number range that spans almost six orders of magnitude in the experiments. The length over diameter aspect ratio of the cylinders ranged from 2.5 to 20. Cylinders were released vertically and rotated to a stable horizontal orientation in most of the lower viscosity solutions. The time required for reaching a horizontal orientation, as well as the Reynolds number at that stage, scale with the Archimedes number and only weakly depend on the aspect ratio. Particle‐resolved numerical simulations based on the lattice‐Boltzmann method complement the experimental study and illustrate the relevance of the experimental data as a benchmark for numerical approaches to solid–liquid flow with non‐spherical particles.

A Bioinspired Adhesive Sucker with Both Suction and Adhesion Mechanisms for Three-Dimensional Surfaces

There are significant advantages to investigate underwater attachments, which would be valuable in providing inspirations and design strategies for multi-functional surfaces and underwater robots. Here, an abalone-inspired sucker integrating an elastic body and a membrane structure is proposed and fabricated filled with rigid quartz particles to adjust the backing stiffness of the contact like abalone. The membrane is used to conform and contact surfaces well, the center area of which can be pulled in exposed to a negative pressure differential, to create a suction cavity. The pulling experiments indicate that the sucker can adhere to three-dimensional surfaces with both suction and adhesion mechanisms in both dry and liquid environments. The switching between soft/hard contact states leads to the change of adhesive strength over 30 times. Furthermore, we provide theoretical analysis on how the sucker work well in both dry and liquid environments. Finally, the developed sucker can easily lift up smooth planar objects and 3D objects, and can grip objects both smaller and larger than the size of the sucker, which have a difficulty for conventional suckers or friction-based grippers. The potential application of the sucker in flexible transfer robot is demonstrated on various surfaces and environments, paving the way for further bio-inspired adhesive designs for both dry and wet scenarios.

Mechanical properties and microstructure of polychlorotrifluoroethylene toughened by polyamide 11 based on intermolecular interaction

AbstractPolychlorotrifluoroethylene (PCTFE) is a promising candidate for cryogenic storage and transportation materials in clean energy industry. But, how to improve its toughness without scarification other performance is still challenging. In this study, the immiscible PA11 is introduced into PCTFE matrix as toughening agent based on a strategy of enhanced interfacial effect. As the incorporation of PA11 increased from 0 to 20 wt%, the toughness of the PCTFE/PA11 shows a trend of first increasing and then decreasing, which reaches the optimal performance with 5 wt% PA11. The elongation at break and impact strength are respectively increased by ~3 and ~1.9 times without obvious reduction of other mechanical performance. Meanwhile, PA11 could enhance the primary nucleation and crystallization ability of PCTFE. With further detailed information of microstructures and Fourier infrared spectra, a multieffect synergistic toughening mechanism based on rigid particle and intermolecular interaction has been elucidated. Furthermore, the toughening of PA11 on PCTFE at ultra‐low temperature of −196°C is confirmed.

Stress–Deformation Response of Rigid–Soft Particulate Mixtures under Repetitive Ko Loading Conditions

Sand–rubber mixtures used in transportation infrastructure experience repetitive loading. Hence, in this study, the mixtures of rigid sand particles and soft tire chip particles with two different size ratios at varying tire chip fractions (TF) by weight were prepared, and repetitive loading tests were performed for 10,000 cycles at 100 kPa stress amplitude (Δσ). The results of this study demonstrate that significant volume contraction occurs for the tested rigid-soft mixtures during repetitive loading due to the continuous accumulation of plastic strain. Most notably, this study reveals that the magnitude of elastic strain recovery of the tested mixtures decreases with increasing cyclic loading number, reflecting the transition of the structural skeleton from the contacts between sand-to-rubber and/or rubber-to-rubber to those between sand-to-sand and/or rubber-to-sand under repetitive loading conditions with constant Δσ. The effects of TF and size ratio on the compressibility of the tested mixtures are also evaluated in this study.

First Report of Tobacco Mosaic Virus Infecting Papaya in China.

Papaya (Carica papaya. L) is widely cultivated in tropical and subtropical regions of China and has high nutritional and medicinal values. More than 11 species of papaya viruses have been recorded in the world, but the most destructive one for papaya production in China is papaya ringspot virus (PRSV) (Li, 2019). In order to control PRSV, a transgenic papaya cultivar, designated as 'Huanong No.1', carrying the nuclear inclusion b (Nib) cistron of PRSV Ys isolate, was successfully commercialized in 2006, and has shown a wide range of resistance to PRSV in China (Li et al. 2007). However, more than 10% of 'Huanong No.1' plants developed different virus-like symptoms on leaves, including mosaic, yellow mottle, and deformation in some plantations of Guangdong Province, China in 2020 (Suppl Figure 1a, b, and c). Based on observation of the symptomatic phenotypes, the field surveys indicated that the disease incidence ranged from 10% to 40%, resulting in significant loss of papaya fruit. The virus particles were purified from symptomatic papaya plants following Gooding and Hebert (1967) and rigid filamentous particles resembling tobacco mosaic virus (TMV) were observed by transmission electron microscopy. Purified virus samples were further utilized to mechanically inoculate healthy seedlings of papaya, Nicotiana glutinosa and N. tabacum K326. At 15 days after inoculation, the obvious symptoms of virus infection on different plants were observed. The diseased plants showed systemic mottling and mosaic in the papaya leaves (Suppl Figure 1d), necrotic spots on the leaves of N. glutinosa (Suppl Figure 1e), mosaic and mottling spots on leaves of N. tabacum K326 (Suppl Figure 1f). These symptoms produced on the hosts were exactly the same caused by TMV. In order to reconfirm the species of the infected virus, the total RNA was extracted from the single leaf of 30 diseased papaya plants using RNAiso Plus kit (Takara, Japan) and reverse transcription--polymerase chain reaction was performed using TMV coat protein cistron specific primers (TMV-CP-R: 5'-TCAAGTTGCAGGACCAGA-3' and TMV-CP-F 5'- ATGTCTTACAGTATCACTAC-3') as described previously (Srivastava et al. 2015). An expected 480-bp fragment was amplified from all of the samples. Sequence analysis revealed that the diseased papaya was infected with TMV, designated as Cpa-TMV. In order to understand the difference among TMV isolates on papaya and other host plants, the whole genomic sequence of TMV from papaya was obtained and analyzed. The total length of the genome of Cpa-TMV was 6395 bp, and the sequence was submitted to the NCBI database (GenBank no. OK149218). A neighbor-joining phylogenetic tree of 19 TMV isolates was constructed using MEGA X software. Phylogenetic analysis indicated that the 19 TMV isolates were divided into Clade I, II and III (Suppl Figure 2). Interestingly, Clade I was composed of 12 Chinese mainland isolates, which further was grouped into IA (Northern China) and IB (Southern China), while 6 isolates from other countries and 1 isolate (pet-TMV) from China Taiwan belong to Clade II and III. It is inferred that the TMV isolates from Chinese mainland are quite different from other countries and China Taiwan. This suggests that geographical differences between Northern and Southern China may lead to the gradual differentiation of TMV isolates and eventually induce those isolates to evolve into two subclades. To our knowledge, this is the first report of TMV infection on papaya under natural conditions. It is necessary to find effective methods to control TMV in transgenic papaya.

A simple model to fit and interpret creep curves-behaviour of modified micro-cellulose particulate composites

Micro crystalline cellulose is mostly used to improve thermo-mechanical properties of composites. This study aims to evaluate the creep behaviour of micro-cellulose epoxy-based composites, and the effect of silanization treatment on the reinforcements. A new viscoelastic model, based on the generalized logistic function was successfully tested. The results were directly associated with the material’s structure–property relationships. Rigid particles restricted the molecular chain’s motion, mainly on the amorphous segments. This difference achieved the needing of more energy, to achieve creep deformation. Then, MCC improved the structural integrity, when incorporated into an epoxy matrix. On one hand, the incorporation of silanized-MCC increased the mechanical behavior of the composite, due to the stiffer structure. Furthermore, the chemical modification provided an increment in the glassy plateau, associated with higher thermal energy required to initiate strain of the amorphous polymeric chains. This behaviour resulted in an abrupt decrease of load-bearing capability for the composites. Finally, the proposed model is suitable to be employed in creep curves, aiming to easily interpret the structure–property relationships of this test. Graphical abstract

Rheo-Engineered Microfluidics @ UNINA

<h2>Abstract</h2> The interest in microfluidic applications based on complex fluids is a result of the unique fluid dynamics of these systems, which enable the creation of effective devices for health care or biological and chemical analysis. In this area, processing suspensions of rigid particles in viscoelastic liquids offers a variety of possible applications where the rheology plays a key role. This contribution presents our activities on viscoelasticity-driven microfluidic applications with rigid particles. The effects of the fluid rheology, particle shape, channel geometry, wall properties, and particle volume fraction are addressed.

Self-toughening of epoxy resin by introduction of highly crosslinked thermoset epoxy microspheres

The theories and technologies concerning polyolefin toughening with rubber or inorganic rigid particle have been studied comprehensively, the results indicated that the toughening with rubber always lowers the modulus and heat resistance of materials. Also, toughening with inorganic rigid particle is not good because of its low dispersion and miscibility with epoxy resin. Monodisperse epoxy microspheres (EMs) with high crosslinking density were prepared with Polypropylene glycol with molecular weight of 600 as the reaction solvent and trifunctional epoxy resin (TDE-85) and aromatic diamine (DETDA) as the precursors. The formation of EMs was investigated in detail. The crosslinked microspheres were used as toughening agent to realize DGEBA/DDS system self- toughening. When adding 5wt% epoxy microspheres, the impact strength improved by 87% and Tg increased more than 6 °C. The results show that the prepared epoxy microspheres with high crosslinking density can not only greatly improve the toughness of epoxy resin, but also improve its heat resistance.

Experimental Studies and Comparative Analyses on Apparent Viscosity of Solid Particle, Droplet, and Bubble Suspensions

Background: Suspensions can be frequently seen in natural, industrial, and agricultural processes. The addition of dispersed phases (such as solid particles, droplets, and bubbles) greatly affects the rheological properties of matrix liquid. Therefore, it is very important to understand the rheological properties of particle suspensions for optimizing production processes and improving process efficiencies. Objective: To explore qualitatively the physical law and internal mechanism of the apparent viscosity of suspensions formed by a Newtonian liquid containing solid particles, droplets, and bubbles, respectively. Methods: The apparent viscosity of suspensions was measured and analyzed using a rotary rheometer (MCR302), and the evolution of particles was recorded using a highspeed camera (Revealer 2F01M). Results: When the deformation of deformable particles (such as bubbles or water droplets) is slight (close to a sphere in shape), or the arrangement of rigid particles is disordered, the relative viscosity of suspensions is greater than 1. When the deformation of deformable particles is large (greatly deviating from a sphere in shape) or rigid particles are arranged in order, the apparent viscosity of suspensions decreases and the relative viscosity of suspensions containing deformable particles is less than 1. Conclusion: The apparent viscosity of suspensions is closely related to particle shape, particle arrangement, and volume fraction. The higher volume fraction of particles significantly influences the apparent viscosity of suspensions.

Effects of Interfacial Shear on Particle Aggregation at an Oil/Water Interface.

Using a Stokesian dynamics simulation, the microstructure of particle aggregates at an oil/water interface with an applied Couette flow is studied. The results of the aggregation are consistent with previously published experimental work demonstrating multiple regimes of behavior based on the relative strength of shear and capillary forces. In previous work, densification of aggregates at low shear rates was theorized to occur due to short time scale fragmentation/reaggregation of aggregates with rigid particle bonds. In simulations, densification is observed at low shear rates but occurs due to local reorganization of particles due to capillary torques over long time scales. Moderate shear rates create mobile bonds between particles at shorter time scales, allowing aggregates to fragment without reaggregation into smaller isolated clusters, consistent with prior experimental work. At the highest shear rates, aggregation is inhibited completely.

Quantitative homogenization theory for random suspensions in steady Stokes flow

This work develops a quantitative homogenization theory for random suspensions of rigid particles in a steady Stokes flow, and completes recent qualitative results. More precisely, we establish a large-scale regularity theory for this Stokes problem, and we prove moment bounds for the associated correctors and optimal estimates on the homogenization error; the latter further requires a quantitative ergodicity assumption on the random suspension. Compared to the corresponding quantitative homogenization theory for divergence-form linear elliptic equations, substantial difficulties arise from the analysis of the fluid incompressibility and the particle rigidity constraints. Our analysis further applies to the problem of stiff inclusions in (compressible or incompressible) linear elasticity and in electrostatics; it is also new in those cases, even in the periodic setting.

Tuning the shear thickening of suspensions through surface roughness and physico-chemical interactions

Shear thickening denotes the reversible increase in viscosity of a suspension of rigid particles under external shear. This ubiquitous phenomenon has been documented in a broad variety of multiphase particulate systems, while its microscopic origin has been successively attributed to hydrodynamic interactions and frictional contact between particles. The relative contribution of these two phenomena to the magnitude of shear thickening is still highly debated, and we report here a discriminating experimental study using a model shear-thickening suspension that allows us to independently tune both the surface chemistry and the surface roughness of the particles. We show here that both properties matter when it comes to continuous shear thickening (CST) and that the presence of hydrogen bonds between the particles is essential to achieve discontinuous shear thickening (DST) by enhancing solid friction between closely contacting particles. Moreover, a simple argument allows us to predict the onset of CST, which for these very rough particles occurs at a critical volume fraction much lower than that previously reported in the literature. Finally, we demonstrate how mixtures of particles with opposing surface chemistry make it possible to finely tune the shear-thickening response of the suspension at a fixed volume fraction, paving the way for a fine control of the shear-thickening transition in engineering applications.

An integrated intumescent flame retardant of bismaleimide from novel maleimide-functionalized triazine-rich polyphosphazene microspheres

In view of the problems of poor toughness and high fire risk of bismaleimide (BMI), a novel maleimide-functionalized triazine-rich polyphosphazene microsphere (PPM) was designed and prepared in this work by combining the flame retardant advantages of polyphosphazene and melamine. The functionalization of organic maleimide in PPM can improve the interfacial compatibility between PPM and BMI. With addition of 2.0 wt% PPM, the peak value of heat release rate (PHRR) and total smoke production (TSP) of BMI/PPM-2.0 decrease by 52.8 % and 30.8 %, respectively, while its impact strength increases by 97.5 %, which means that the fire safety and toughness of BMI/PPM are much better. The study on flame retardant mechanism of PPM reveals that PPM has obvious condensed-phase intumescent flame-retardant effect, which may be due to the similar composition of PPM and intumescent flame retardant. In addition, PPM has the phosphorus-oxygen radical flame-retardant effect in gas phase and also has the toughening effect of inorganic rigid particles on BMI performance.

A generalised drift-correcting time integration scheme for Brownian suspensions of rigid particles with arbitrary shape

The efficient computation of the overdamped, random motion of micron and nanometre scale particles in a viscous fluid requires novel methods to obtain the hydrodynamic interactions, random displacements and Brownian drift at minimal cost. Capturing Brownian drift is done most efficiently through a judiciously constructed time-integration scheme that automatically accounts for its contribution to particle motion. In this paper, we present a generalised drift-correcting (gDC) scheme that accounts for Brownian drift for suspensions of rigid particles with arbitrary shape. The scheme seamlessly integrates with fast methods for computing the hydrodynamic interactions and random increments and requires a single full mobility solve per time-step. As a result, the gDC provides increased computational efficiency when used in conjunction with grid-based methods that employ fluctuating hydrodynamics to obtain the random increments. Further, for these methods the additional computations that the scheme requires occur at the level of individual particles, and hence lend themselves naturally to parallel computation. We perform a series of simulations that demonstrate the gDC obtains similar levels of accuracy as compared with the existing state-of-the-art. In addition, these simulations illustrate the gDC's applicability to a wide array of relevant problems involving Brownian suspensions of non-spherical particles, such as the structure of liquid crystals and the rheology of complex fluids.

Role of cohesion in the flow of active particles through bottlenecks

We experimentally and numerically study the flow of programmable active particles (APs) with tunable cohesion strength through geometric constrictions. Similar to purely repulsive granular systems, we observe an exponential distribution of burst sizes and power-law-distributed clogging durations. Upon increasing cohesion between APs, we find a rather abrupt transition from an arch-dominated clogging regime to a cohesion-dominated regime where droplets form at the aperture of the bottleneck. In the arch-dominated regime the flow-rate only weakly depends on the cohesion strength. This suggests that cohesion must not necessarily decrease the group’s efficiency passing through geometric constrictions or pores. Such behavior is explained by “slippery” particle bonds which avoids the formation of a rigid particle network and thus prevents clogging. Overall, our results confirm the general applicability of the statistical framework of intermittent flow through bottlenecks developed for granular materials also in case of active microswimmers whose behavior is more complex than that of Brownian particles but which mimic the behavior of living systems.

Inertial focusing of particles and cells in the microfluidic labyrinth device: Role of sharp turns.

Inertial, size-based focusing was investigated in the microfluidic labyrinth device consisting of several U-shaped turns along with circular loops. Turns are associated with tight curvature and, therefore, induce strong Dean forces for separating particles; however, systematic studies exploring this possibility do not exist. We characterized the focusing dynamics of different-sized rigid particles, cancer cells, and white blood cells over a range of fluid Reynolds numbers . Streak widths of the focused particle streams at all the turns showed intermittent fluctuations that were substantial for smaller particles and at higher . In contrast, cell streaks were less prone to fluctuations. Computational fluid dynamics simulations revealed the existence of strong turn-induced Dean vortices, which help explain the intermittent fluctuations seen in particle focusing. Next, we developed a measure of pairwise separability to evaluate the quality of separation between focused streams of two different particle sizes. Using this, we assessed the impact of a single sharp turn on separation. In general, the separability was found to vary significantly as particles traversed the tight-curvature U-turn. Comparing the separability at the entry and exit sections, we found that turns either improved or reduced separation between different-sized particles depending on . Finally, we evaluated the separability at the downstream expansion section to quantify the performance of the labyrinth device in terms of achieving size-based enrichment of particles and cells. Overall, our results show that turns are better for cell focusing and separation given that they are more immune to curvature-driven fluctuations in comparison to rigid particles.

Directed transport of a deformable particle in confined periodic structures

Directed transport of a deformable particle is numerically investigated in a two-dimensional periodic channel. Unlike the rigid particle, the deformable particle can pass through the channel bottleneck that is significantly smaller than the particle size. The deformable characteristics of the particle can greatly affect the directed transport of the particle. (i) For the case of active deformable particle, the self-propelled velocity can break thermodynamics equilibrium and induce the directed transport. The average velocity is a peak (or valley) function of the particle size for large (or small) self-propulsion speed. Particle softening (large shape parameter) facilitates the rectification of the particle for small particle, while it blocks the rectification for large particle. (ii) For the case of passive deformable particle, periodic oscillation of the particle size can also break thermodynamical equilibrium. There exists an optimal oscillating frequency at which the average velocity takes its maximal value. For low oscillating frequency, the average velocity is a peak function of the oscillating amplitude, while for high oscillating frequency the average velocity increases monotonically with the oscillating amplitude. Our results may contribute to the understanding of the transport behaviors of soft, deformable matter in confined structures.

Direct observation of the microfiltration of yeast cells at the micro-scale: Characterization of cake properties

This study examines the accumulation of yeast cells at the membrane surface and the morphology of the formed cake through microscale monitoring and analysis of the microfiltration process. An original dead-end microfiltration device with a model membrane was designed and coupled with an optical imaging system to provide direct observation from the side, allowing in-situ real time study of the filtration operation (Valencia et al. 2020 [1]). Here, the deposition of yeast cells, monodispersed and polydispersed particles, in the same size range that yeast cells, was analyzed. Image processing was used to perform a quantitative characterization of cake morphological properties in terms of height, porosity, permeability, Kozeny coefficient and specific resistance. The cakes formed by monodispersed spherical and non-spherical rigid particles exhibit a similar incompressible behavior with higher porosity than yeast cakes, with mean porosity values of 0.38 for the rigid particles and 0.15 for the yeast at the end of the filtration run, respectively. The cake obtained by the microfiltration of a model suspension of polydispersed particles close to yeast size and shape is more compact (porosity of 0.29) and less permeable. However, polydispersity does not fully explain yeast cake properties, in particular its compressibility. Indeed, the yeast cake has a high compressibility index n = 1.1, which is reflected in a significant volume expansion of the yeast cake after transmembrane pressure was removed.