Rough Particles Research Articles

Effect of interface roughness on mechanical properties of layered cemented tailings backfill

Research on the roughness parameters of the layered interface of the layered cemented tailings backfill (LCTB) is of great significance to improve the cementation quality of layered layers and reduce the strength reduction rate caused by layering for the safety and stability of the mine structure. Using the sedimentation mechanism of tailing sand particles, different roughness interfaces with different solid densities (SDs) and number of layered layers were designed, and the influence mechanism of interface roughness on the cementation quality of layered layers was studied by using uniaxial compression test, surface roughness detection and particle size detection. The results show that the existence of stratified surfaces can significantly reduce the uniaxial compressive strength (UCS) of the LCTB, which is defined here as the Stratified reduction rate (SRR).When the number of stratified layers is constant, the strength reduction rate caused by stratified layers decreases with the increase of SD, and the increase of SD will increase the shear resistance of the coarse particles in the slurry, making it less prone to segregation and subsidence. As a result, the larger the proportion of coarse particle size distribution on the layered surface, the macroscopic surface roughness increases. The SRR has a good linear fitting relationship with surface roughness Ra, and the SRR decreases with the increase of Ra, indicating that to a certain extent, the greater the surface roughness of the stratified plane, the better the cementation quality of the delamination surface, and the weaker the reduction effect of the delamination on the strength of the LCTB.

Cashew Nutshells: A Promising Filler for 3D Printing Filaments.

Cashew nutshells from the northern region of Colombia were prepared to assess their potential use as a filler in polymer matrix filaments for 3D printing. After drying and grinding processes, cashew nutshells were characterized using scanning electron microscopy (SEM), attenuated total reflectance Fourier-transform infrared (ATR-FTIR), and thermogravimetric analyses (TGA). Three different filaments were fabricated from polylactic acid pellets and cashew nutshell particles at 0.5, 1.0, and 2.0 weight percentages using a single-screw extruder. Subsequently, single-filament tensile tests were carried out on them. SEM images showed rough and porous particles composed of an arrangement of cellulose microfibrils embedded in a hemicellulose and lignin matrix, the typical microstructure reported for natural fibers. These characteristics observed in the particles are favorable for improving filler-matrix adhesion in polymer matrix composites. In addition, their low density of 0.337 g/cm3 makes them attractive for lightweight applications. ATR-FTIR spectra exhibited specific functional groups attributed to hemicellulose, cellulose, and lignin, as well as a possible transformation to crystalline cellulose during drying treatment. According to TGA analyses, the thermal stability of cashew nutshell particles is around 320 °C. The three polylactic acid-cashew nutshell particle filaments prepared in this work showed higher tensile strength and elongation at break when compared to polylactic acid filament. The characteristics displayed by these cashew nutshell particles make them a promising filler for 3D printing filaments.

Polymyxin B sulfate inhalable microparticles with high-lectin-affinity sugar carriers for efficient treatment of biofilm-associated pulmonary infections

Pulmonary infections caused by multidrug-resistant bacteria have become a significant threat to human health. Bacterial biofilms exacerbate the persistence and recurrence of pulmonary infections, hindering the accessibility and effectiveness of antibiotics. In this study, a dry powder inhalation (DPI) consisting of polymyxin B sulfate (PMBS) inhalable microparticles and high-lectin-affinity (HLA) sugar (i.e., raffinose) carriers was developed for treating pulmonary infections and targeting bacterial lectins essential for biofilm growth. The formulated PMBS-HLA DPIs exhibited particle sizes of approximately 3 μm, and surface roughness varied according to the drug-to-carrier ratio. Formulation F5 (PMBS: raffinose = 10:90) demonstrated the highest fine particle fraction (FPF) value (64.86%), signifying its substantially enhanced aerosol performance, potentially attributable to moderate roughness and smallest mass median aerodynamic particle size. The efficacy of PMBS-HLA DPIs in inhibiting biofilm formation and eradicating mature biofilms was significantly improved with the addition of raffinose, suggesting the effectiveness of lectin-binding strategy for combating bacterial biofilm-associated infections. In rat models with acute and chronic pulmonary infections, F5 demonstrated superior bacterial killing and amelioration of inflammatory responses compared to spray-dried PMBS (F0). In conclusion, our HLA carrier-based formulation presents considerable potential for the efficient treatment of multidrug-resistant bacterial biofilm-associated pulmonary infections.

Rough colloids at fluid interfaces: from fundamental science to applications

Colloidal particles pinned to fluid interfaces have applications ranging from Pickering emulsions and foams to the development of 2D materials via Langmuir-Blodgett deposition. While colloids come in virtually any size, shape, and chemistry, particle surface topography, or roughness, has recently found renewed interest as a design parameter for controlling interfacial pinning, capillary interactions, assembly, and mechanics of particulate monolayers. In this review, we highlight the fundamental science regarding rough colloidal particles at fluid interfaces and how manipulating roughness can be a tool for material design, rather than merely a characteristic needing to be dealt with. While existing work reveals the importance of roughness, the field is still rather nascent and therefore this review highlights both challenges and opportunities for future research.

Numerical simulation of the particle wall mass transfer rates on rough surfaces confining turbulent natural convection flows

We performed numerical simulations of the particle mass transfer rates on the horizontal and vertical thermally active rough walls confining a turbulent natural convection flow. We considered the air flow conditions in a cubical cavity (L=1.22m, Ra=5.4·108, Pr=0.71) with two opposed pairs of consecutive walls at different temperatures, for which measurements of the particle deposition velocities are reported in the literature. The simulations were carried out by solving the momentum, thermal energy and particle mass transfer equations using a series of two-dimensional computational cell units to determine spatial evolution and development of the particle concentration boundary layer in the vicinity of hot and cold rough walls. Different flow conditions, wall orientations, sizes of roughness elements, particle diameters and temperature increments between the wall and the bulk fluid, typically found in indoor environments, have been considered and consequently, results can be used to estimate the particle deposition rates in real scenarios. At large mass transfer particle Péclet numbers, corresponding to spherical particles with diameters of 0.5–1 μm, the wall mass transfer rates of particles on rough textures typically increase by a factor of about 3 in comparison with the deposition on smooth surfaces. The thermophoretic effect significantly decreases the particle deposition on hot surfaces and increases it on cold surfaces, especially at large particle Péclet numbers. The numerical predictions of the deposition velocities are in good agreement with the measurements reported in the literature for the same flow conditions considered.

The effect of surface roughness on the viscoelastic energy dissipation in a particle–wall collision

The particle collision on a wall with roughness is common in nature and industries, but not well understood yet. The presence of surface roughness greatly increases the complexity of local contact and makes it difficult to predict the energy dissipation by analytical models. In this work, we investigate the energy dissipation in a dynamic particle–wall collision with regular hemisphere roughness. The finite element method (FEM) with the standard linear solid model is used to solve the problem of non-ideal geometry, and extract the law of energy dissipation due to viscoelasticity. The results show that with the existence of surface roughness, the total viscoelastic dissipation is lower than that for a smooth surface, showing a higher restitution coefficient compared to the smooth surface. Based on the maximum number of asperities that particle contacts, the dynamic collisions can be categorized as the single-contact mode and multiple-contact mode. The variation of the total energy dissipation shows opposite trends with the roughness height in the two different modes. The collision time is recognized as the key to predict the total energy dissipation. Based on FEM simulation results, a piecewise correlation is established to estimate the Hertzian collision time with regular roughness. Finally, a correlation is proposed for the total energy dissipation in a viscoelastic particle–wall collision with regular roughness, which only takes the dimensionless relaxation time as the parameter. Covering different roughness heights, particle sizes, densities, relaxation times, and Young’s modulus, all the data are well correlated with the predicted curve.

Optimizing the formulation variables for encapsulation of linezolid into polycaprolactone inhalable microspheres using double emulsion solvent evaporation

Inhaled antibiotics delivered through dry powder inhalers (DPIs) effectively treat severe bacterial infections by directly targeting the lungs. Our study focused on developing inhalable dry powder microspheres of linezolid (LNZ) using biodegradable polycaprolactone (PCL) polymer. The LNZ-PCL microspheres were fabricated using a double emulsification solvent evaporation method. Optimization of formulation parameters was performed using a factorial design. Evaluation of the microspheres included size, shape, drug loading, entrapment efficiency, aerosolization, and drug release. The morphological analysis confirmed spherical-shaped rough particles within the inhalable size range. The encapsulation efficiency was determined to be 52.84%, indicating successful drug incorporation. Aerosolization efficiency was significantly enhanced when LNZ-PCL microspheres were combined with lactose as a carrier, achieving a fine particle fraction (FPF) value of 70.90%. In-vitro dissolution studies demonstrated sustained drug release for over 24 h under lung pH conditions. Overall, our study highlights the potential of inhalable LNZ-PCL microspheres as a targeted approach for treating pulmonary tuberculosis. Further research and in-vivo studies are needed to validate their effectiveness in life-threatening bacterial infections.

Evaluating uncertainty in particle roughness of coated sand and its implication to coating abrasion

Coated soils have recently been spotlighted for their prospective applications in geotechnical engineering. Prior studies have shown that Polydimethylsiloxane (PDMS) coatings can substantially mitigate surface roughness and have suggested that such coatings may experience abrasion under stress conditions. However, comprehensive studies exploring the impacts of these coatings on particle surface attributes have been scarce. In this work, we scrutinize the surface properties of coated sands with varying mass ratios (MRs), applying probabilistic analysis to account for inherent uncertainty. According to the uncertainty quantification investigation via experimental data, the Gamma distribution is optimal to examine increasing MRs, highlighting a steady decline in surface roughness and corresponding dispersion. Furthermore, a probabilistic assessment of a specific coated sand sample (3% MR) exposed to different stress levels are conducted. The findings suggest that polymer coatings may endure abrasion as stress levels rise, with the average roughness values incrementally converging towards those of natural sands. The detailed examination of particle surface characteristics also unveils the existence of more pronounced peaks and valleys at elevated stress levels, implying significant height variations and evident heterogeneity in surface profiles. Overall, the use of probabilistic analysis techniques provides a more precise understanding of how particle surface properties depend on increasing MRs and their notable dispersion under escalating stress levels. This methodology could be instrumental in probing the mechanical behavior of coated sands, known for their considerable uncertainty.

The Effects of Ball-Mill Grinding Parameters on Lignite Morphology

In recent years, because of the decreasing liberation sizes of the minerals, processes such as grinding need to be evaluated in more detail. As is well known, size reduction processes are very important both in mineral processing and in many industrial applications. However, to increase the efficiency of the processes after size reduction, variations in particle morphology should also be evaluated, along with particle size. Although the effectiveness of grinding media (ball, rod, autogenous) has been shown for different materials, there are very few studies on the effect of the powder/grinding media ratio and grinding time on particle morphology in terms of shape factor and roughness values. This study aims to investigate the variations in the morphology of lignite samples under different grinding conditions such as grinding time and powder/grinding media ratio (U). The results of these analyses showed that while the d80 size of the ground lignite was 1.1 mm after 2 min grinding time, it decreased to 0.5 mm following 15 min grinding time. The roundness values of particles vary in the range of 0.746–0.790 with increasing grinding time. In addition to the grinding time, while the roundness of particles was found to be 0.739 for 0.34 U values (powder/grinding medium rate), it increased to 0.788 when the U value was adjusted to 0.67. The average roughness (Ra) values of particles increased from 60.9 nm to 107.9 nm upon increasing the grinding time from 2 min to 16 min. Due to these findings, it can be suggested that lignite samples became rounder with increasing grinding times, and roughness analyses made in a 10 × 10 μm surface area with an Atomic Force Microscope (AFM) indicated that particle roughness increased in direct proportion to grinding time.

Improved quality and inhibited aggregation of Ag–In alloy films

Ag atoms agglomeration at environmental conditions limits its applications. Here, the influences of indium addition on the microstructure and performance of Ag films were investigated. The results show that the particle size, pore size, and roughness of Ag–In alloy films are greatly reduced compared with those of the Ag film. A small amount of indium can efficiently inhibit the agglomeration/migration of Ag atoms and thus significantly improve the reflective performance at damp heat environment. These results show that alloying is an effective method to inhibit Ag atoms migration/agglomeration at environmental conditions.

Superhydrophilic and underwater superoleophobic PVDF-PES nanofibrous membranes for highly efficient surfactant-stabilized oil-in-water emulsions separation

Deep oil-water emulsions separation is a challenging task for oily wastewater treatment. Herein, a superwettable nanofibrous membrane was fabricated using the integrated method of electrospinning, microwave-assisted growth, and in-situ polymerization. The membrane possessed superhydrophilicity and underwater superoleophobicity due to the presence of hierarchical rough structures and hydrophilic particles and polymers. The nanofibrous membrane exhibited robust oil-water separation performances for surfactant-free oil-in-water emulsions and different types of surfactant-stabilized emulsions (e.g., SDBS, CTAB and Tween 80) solely under the effect of gravity. The membrane achieved a separation efficiency of >99.94% for surfactant-free oil-in-water emulsions with a flux of 3563.0 L m−2 h−1. The efficiency was above 98.90% with a flux of 1112.5 L m−2 h−1 for SDBS-stabilized oil-in-water emulsion solely under the effect of gravity. The membrane exhibited long-term oil-water separation efficiencies of above 97.0%. Moreover, the membrane showed remarkable stability and can maintain underwater superoleophobicity under different harsh conditions, which is key for large-scale oily wastewater treatment applications.

Toughening colloidal gels using rough building blocks

Colloidal gels, commonly used as mesoporous intermediates or functional materials, suffer from brittleness, often showing small yield strains on the order of 1% or less for gelled colloidal suspensions. The short-range adhesive forces in most such gels are central forces—combined with the smooth morphology of particles, the resistance to yielding and shear-induced restructuring is limited. In this study, we propose an innovative approach to improve colloidal gels by introducing surface roughness to the particles to change the yield strain, giving rise to non-central interactions. To elucidate the effects of particle roughness on gel properties, we prepared thermoreversible gels made from rough or smooth silica particles using a reliable click-like-chemistry-based surface grafting technique. Rheological and optical characterization revealed that rough particle gels exhibit enhanced toughness and self-healing properties. These remarkable properties can be utilized in various applications, such as xerogel fabrication and high-fidelity extrusion 3D-printing, as we demonstrate in this study.

Influence of processing temperature on production of red beetroot powder as a natural red colorant using foam-mat drying: Experimental and modeling study.

With high medicinal and nutritional value, red beetroot powder is utilized as a natural pigment and functional additive in various food industries. In this investigation, red beetroot powder was produced using foam-mat drying, and the effect of drying temperature on quality attributes was evaluated. Computer simulation was also performed to assess the impact of temperature on uniformity of moisture loss and temperature during drying. Temperature variations did not exert a significant impact on water solubility and total color difference of the powders. Images obtained from field emission scanning electron microscopy illustrated that with increasing temperature, wrinkling, cracking, and roughness of the powder particles reduced because of the formation of smooth and hard crusts on the particles' surface. Predicted moisture content values were in good agreement with measured data. The results of this study could be used to optimize foam-mat drying of red beetroot to produce functional powders with suitable physicochemical and microstructural characteristics.

Numerically investigation of the neutron irradiation swelling on the mechanical and structural evolution of beryllium pebble bed

Pebble bed is employed in the blanket system to achieve neutron multiplication and tritium breeding. Neutron irradiation among the pebble bed is inevitable when the tokamak device is in normal operation. Particles could be swelled and the formation of bubbles or pore on the surface could aggravate the roughness of particles the surface under irradiation. It has great impact of pebble bed structure. In this paper, the mechanical and structure characteristics of the Beryllium (Be) pebble bed in the Helium Coolant Ceramic Breeding (HCCB) blanket were investigated. Furthermore, the evolution process of the pebble bed with mesoscale is analyzed as well. The Discrete Element Method (DEM) with Particle Flow Code (PFC) software is utilized to simulate the variation of particles under neutron irradiation with different roughness of particle surfaces and irradiation doses. Meanwhile, 0, 1%, 2%, 4% and 6% irradiation of single particle in radius direction with 0, 0.1, 0.3 and 0.5 friction coefficients were assumed. The evolution of the local packing factor, coordination number, contact force and force chain are given, and the fabric analysis is also given. The results show that the irradiation swelling of the particles and the deterioration of the surface have great impacts on the structure and mechanical properties of the pebble bed under neutron irradiation. Particle swelling could improve the packing factor and coordination number of the pebble bed, and the contact force distribution. The deterioration of the particle surface reduces the coordination number and shortens the force chain length. This paper presents the working condition under neutron irradiation which could provide reference for the design and evaluate of the blanket pebble bed.

Evolution of particle morphology of quartz sand during one-dimensional compression

Particle breakage alters particle size, shape, surface roughness, and co-ordination number, which in turn changes macro-mechanical behaviour including compressibility and shear strength. This study conducted a series of one-dimensional (1D) compression tests on quartz sands with different initial void ratios, ending the tests at various stress levels up to 13.5 MPa. The size and shape of particles were quantified using a dynamic particle shape analyser, while the surface roughness of thirty randomly selected particles for each sample was measured by an optical interferometer and quantified using flattened root-mean-square roughness (RMSf). The results demonstrate that a unique normal compression line is defined due to extensive particle breakage, with denser sample exhibiting a higher yield stress. Prior to yielding (vertical stress < 6 MPa), the changes in the three shape descriptors are limited, as the primary particle damage modes are abrasion and grinding. Conversely, at high stress level, a greater number of particles undergo splitting or explosive damage, leading to the creation of more irregularly shaped particles. The occurrence of plastic deformation at particle asperities under one-dimensional compression is identified, resulting in a decrease in surface roughness. This study highlights the significant role of the initial void ratio in shaping the evolution of surface roughness of particles under 1D compression.

Engineering the surface patchiness and topography of polystyrene colloids: From spheres to ellipsoids

HypothesisColloidal surface morphology determines suspension properties and applications. While existing methods are effective at generating specific features on spherical particles, an approach extending this to non-spherical particles is currently missing. Synthesizing un-crosslinked polymer microspheres with controlled chemical patchiness would allow subsequent thermomechanical stretching to translate surface topographical features to ellipsoidal particles. ExperimentsA systematic study using seeded emulsion polymerization to create polystyrene (PS) microspheres with controlled surface patches of poly(tert-butyl acrylate) (PtBA) was performed with different polymerization parameters such as concentration of tBA monomer, co-swelling agent, and initiator. Thermomechanical stretching converted seed spheres to microellipsoids. Acid catalyzed hydrolysis (ACH) was performed to remove the patch domains. Roughness was characterized before and after ACH using atomic force microscopy. FindingsPS spheres with controlled chemical patchiness were synthesized. A balance between two factors, domain coalescence from reduced viscosity and domain growth via monomer absorption, dictates the final PtBA) patch features. ACH mediated removal of patch domains produced either golf ball-like porous particles or multicavity particles, depending on the size of the precursor patches. Patchy microspheres were successfully stretched into microellipsoids while retaining their surface characteristics. Particle roughness is governed by the patch geometry and increases after ACH. Overall, this study provides a facile yet controllable platform for creating colloids with highly adjustable surface patterns.

Prediction of fluidization behaviors of rough sphere with a TFM-DEM hybrid model

Some industrial processes like biomass combustion and gasification involve multi-component fluidization systems with a clear discrepancy of particle size, which restricts the utilization of some traditional simulation methods. In this work, a TFM-DEM hybrid model is employed to evaluate flow behaviors of binary mixture in a fluidized bed reactor with a great discrepancy of particle size, where the rotational effect of bed material is described by the kinetic theory of rough sphere (KTRS) and the fluctuating energy transfer between discrete particles and continuous solid phase is considered. The model prediction is validated by the experimental result. The results reveal that considering the collisional effect on solid-solid interaction, bed material fluctuating energy is weakened and more energy is transferred to fuel particles. Meanwhile, the ratio of collisional dissipation to total energy consumption with particle roughness is also analyzed.

Experimental study on the effect of high-temperature nitrogen immersion on the nanoscale pore structure of different lithotypes of coal

This paper presents the heat treatment study on different lithotypes of coal using a custom designed high-temperature thermal nitrogen immersion experimental setup. The results revealed that the heat treatment significantly increased the surface roughness of coal particles and the structural complexity. The pores with diameters >200 nm of coal increased after heat treatment. Some of the new fissures still retain the pore morphology, exhibiting the pore connections. With increasing heat treatment temperature, the total pore volume (TPV) and specific surface area (SSA) of all four selected coal types tended to decrease. Thermal action also significantly increased the average and maximum pore diameters, and the most obvious effect was observed after heat treatment at 120 °C and 210 °C. After heat shock at 210 °C, the average diameters of bright and semibright coal samples were enlarged by 3.5 and 2.7 times, respectively. The semidull coal enlarged 1.6 times, and the dull coal enlarged 1.2 times. In addition, the fractal dimension, which represents the surface roughness of pores, continued decreasing as the heat treatment temperature increases. The pore structure fractal dimension first tends to increase, then decrease, and finally increase again. Therefore, the heat treatment enhanced connectivity and increased fracture, facilitating the transport of methane.

An analytical energy-balance model for restitution coefficient of a dry particle when impacting on a wet plane

The restitution coefficient of particle is a key parameter for simulations of particle-fluid systems. An analytical model based on particle energy balance is proposed for a system of a dry particle impacting on a wet plane. The proposed model incorporates typical mechanisms of particle energy dissipation. For the cases from F. Gollwitzer, et al. (Phys. Rev. E 86 (2012), 011303), dominant dissipation originates from viscous force, whereas energy loss, due to liquid film inertia, cannot be neglected and even takes over system of Reynolds number higher than 90; energy dissipation induced by capillary force is commonly negligible with capillary number of 0.12–4.6. With consideration of particle roughness effects, the model achieves a good agreement with experimental data widely collected from literature. Using more than 800 points from literature, an artificial neural network tool is also developed. As inputs, Stokes, Weber, Reynolds, Bond, and capillary numbers could provide the best prediction.

Special Packaging Materials from Recycled PET and Metallic Nano-Powders.

The European methodology for plastics, as a feature of the EU's circular economy activity plan, ought to support the decrease in plastic waste. The improvement of recycled plastics' economics and quality is one important part of this action plan. Additionally, achieving the requirement that all plastic packaging sold in the EU by 2030 be recyclable or reusable is an important objective. This means that food packaging materials should be recycled in a closed loop at the end. One of the most significant engineering polymers is polyethylene terephthalate (PET), which is widely used. Due to its numerous crucial qualities, it has a wide variety of applications, from packaging to fibers. The thermoplastic polyolefin, primarily polyethylene and polypropylene (PP), is a popular choice utilized globally in a wide range of applications. In the first phase of the current experiment, the materials were obtained by hot pressing with the press machine. The reinforcer is made of Al nanopowder 800 nm and Fe nanopowder 790 nm and the quality of the recycled polymer was examined using Fourier transform infrared spectroscopy (FTIR), a scanning electron microscope (SEM), and differential scanning calorimetry (DSC). From DSC variation curves as a function of temperature, the values from the transformation processes (glass transition, crystallization, and melting) are obtained. SEM measurements revealed that the polymer composites with Al have smooth spherical particles while the ones with Fe have bigger rough spherical particles.