A compression model that elucidates the compressibility of a granular soil assembly is useful for engineering and mechanical applications. While the literature offers numerous compressibility models for granular soils, a significant limitation arises because these models overlook the impact of soil composition. Typically, soils consist of a blend of sand and silt as a result of geological processes. Moreover, empirical observations indicate a substantial influence of silt content on the compressional behavior of bi-dispersed granular soils. This study introduces an approach grounded in a more rigorous theoretical foundation for predicting the compression of bi-dispersed packings. The analytical method is based on Edwards thermodynamics, which is a realm of physics. Within this framework, the analytical method incorporates the excess free volume resulting from the dispersity of the bi-dispersed particle packing. An evaluation was conducted to validate the model’s applicability by comparing the predictions with the experimental results for Hokksund sand-silt mixtures.

Particle shape plays a critical role in governing the properties and behavior of granular materials. Despite advances in capturing and analyzing 3D particle shapes, these remain more demanding than 2D shape analysis due to the high computational costs and time-consuming nature of 3D imaging processes. Consequently, there is a growing interest in exploring potential correlations between 3D and 2D shapes, as this approach could potentially enable a reasonable estimation of a 3D shape from a 2D particle image, or at most, a couple of images. In response to this research interest, this study provides a thorough review of previous studies that have attempted to establish a correlation between 3D and 2D shape measures. A key finding from the extensive review is the high correlation between 2D perimeter circularity (c_p) and Wadell’s true sphericity (S) defined in 3D, suggesting that a 3D shape can be estimated from the c_p value in terms of S. To further substantiate the correlation between c_p and S, this study analyzes approximately 400 mineral particle geometries available from an open-access data repository in both 3D and 2D. The analysis reveals a strong linear relationship between S and c_p compared with other 2D shape descriptors broadly used in the research community. Furthermore, the limited variance in c_p values indicates that c_p is insensitive to changes in viewpoint, which indicates that fewer 2D images are needed. This finding offers a promising avenue for cost-effective and reliable 3D shape estimation using 2D particle images.

Rapid development of antibiotic resistance in pathogenic bacteria and a decline in the pharmaceutical development of new antibiotics are pushing the research community to explore alternative antimicrobials that can replace or complement antibiotics. Bacteriophages (or, phages) are naturally occurring viruses that can kill bacteria with high specificity and can evolve to target resistant bacteria. Phages have been historically employed as antimicrobial agents, but they were overshadowed by the emergence of antibiotics. With a renewed focus on phages, it is important to study their clinical efficacy, safety, and formulation. Pulmonary infections have a large burden of global morbidity and frequently involve multidrug-resistant pathogens such as Acinetobacter baumannii, Klebsiella pneumoniae, Mycobacterium tuberculosis, and Pseudomonas aeruginosa. Therefore, this can be an important area of application of phages. Dry powder inhalers can be an effective strategy to deliver phages to the lungs because they are easy-to-use, portable, and capable of delivering a higher lung dose than oral or intravenous route. They also have longer shelf life and lower cold storage requirements than solutions. Therefore, the aim of the current review is to summarize recent findings on bacteriophage dry powder formulations, particularly focusing on the effect of various excipients and manufacturing factors on phage titer preservation.

Airborne pathogens such as bacteria, viruses and fungi pose significant threats to human health. Various mitigation strategies have been developed, including air filtration, ventilation, UV irradiation, and photocatalytic oxidative disinfection (POD). In particular, the combination of passive air filtration and active POD has promise for the better inactivation of airborne pathogens. However, the efficiency of POD remains hindered by numerous factors, such as inherent fast charge recombination, limited understanding of the interactions between airborne pathogens and catalyst surfaces, and short migration distances of reactive oxygen species (ROS). This perspective elucidates the fundamental principles and constraints of POD and provides several examples for delineating enhancement strategies. The primary objective of this study is to cultivate a cellular-level understanding of the interactions occurring at the biointerfaces in POD systems, thereby revealing the mechanistic pathways and paving the way for future catalyst designs to improve air quality.

In this study, we explore the intersection of mechanical testing and particle imaging techniques, offering a new perspective on granular material science. We examine a range of flow testers, such as the Schulze shear tester, FT4 powder flow tester, and split-bottom tester, each of which provides valuable insights into how materials respond to compression and shear forces. Simultaneously, we discuss imaging techniques such as refractive index matching, MRI, and X-ray imaging, revealing their capacity to capture the intricate behaviours of particles and flow dynamics at a microscopic level. This combination of macroscopic flow testing and microscopic imaging promises to unlock unprecedented insights into granular materials and complex fluids. Furthermore, we discuss the current challenges in imaging granular flows and recent advances in coupling flow tests with particle imaging.

The control of adhesion and aggregation behaviour in gases, liquids, and solids is important for the application of inorganic nano- and fine particles in various fields, such as functional materials and devices, pharmaceuticals, cosmetics, and pigments. We have developed original methods for the characterisation of interfacial molecular- and nanometre-scale structures and interactions between particles and substrate materials. The surface molecular-structure design by an organic surfactant, commonly called a “ligand,” was investigated with different molecular structures for nanoparticle-dispersion stability control in various organic solvents and polymer solid materials. First, we introduce various approaches for controlling the interfacial molecular structure of nanoparticles to disperse nanoparticles in various liquids. Next, aggregation- and adhesion-behaviour characterisation methods, such as colloid probe atomic force microscopy and the control of fine powders and microcapsules in the ceramic and pharmaceutical fields, are reviewed. Finally, the characterisation and control of the adhesion behaviour of fine ash particles at high temperatures in energy generation and environmental systems are investigated. Original characterisation devices and a model of an ash-particle preparation method from pure silica were developed by adding small amounts of elements, such as alkali metals and phosphates, to analyse the increase mechanism of the ash-adhesion force at high temperatures. Based on the results of the analysis, the adhesion behaviour can be controlled by the addition of various materials.

In KONA 2022, the fundamentals of two- and multidimensional particle size distributions were introduced. The next question in the field of two- and multidimensional distributions addresses their application to describe a particle process, e.g., agglomeration or separation. A multidimensional separation can be seen as retrieving only particles with a specific set of properties from a multidimensionally distributed system, e.g., retrieving only small particles (below a certain threshold in size) with a compact spherical shape (above a certain threshold in sphericity). The multidimensional separation allows the generation of functional particle systems with specific properties, e.g., semiconducting, optical, or electronic properties, which are required for high-technology applications. Starting from so-called particle-discrete information, i.e., an information vector for each particle containing its compositional, geometrical, and physical properties, it is possible to describe a multidimensional separation in full detail based on various properties. Each particle can be evaluated according to different separation properties, e.g., size, shape, and material composition. With this database, it is possible to define and work with separation functions to describe the multidimensional separation and quantify the separation results. For example, in the two-dimensional case, the median cut size becomes a median cut line, where the probability for a particle to belong to the concentrate is 0.5. Some case studies and examples show different approaches and possibilities to achieve a multidimensional separation in one or several connected process steps.

Antimicrobial resistance presents a critical challenge to public health, driving the exploration of innovative strategies against microbial threats. Soft solids, notably polyelectrolyte gel complexes, offer promising antimicrobial alternatives with tailored physiochemical properties and biocompatibility. Primarily, soft solids incorporating chitosan and polyacrylic acid (PAA) complexes have gained importance for their antimicrobial efficacy, stemming from electrostatic interactions between oppositely charged components. This paper evaluates non-covalent interactions within chitosan and polyacrylic acid complexes to reduce Escherichia coli (E. coli) contaminants. Chitosan, derived from chitin, is valued for its biodegradability and low toxicity, and is currently used in drug delivery and wound healing systems. Conversely, PAA is an anionic polymer with carboxylic groups, widely used in pH-sensitive hydrogel-based drug delivery systems. In the present study, the antimicrobial effectiveness of chitosan and polyacrylic acid complexes was examined both in solution and on the bio-surface. Distinct patterns of antimicrobial activity were observed at the surface when applied individually and in combination. A synergistic antimicrobial effect of the chitosan and polyacrylic acid complex (gel particles), resulted in a remarkable reduction in viable cells both in solution and on the surface. This understanding enhances the potential use of soft solids in addressing the challenge of deactivating antimicrobial resistance pathogens.

The rheological characterization of mineral slurries is a complex task, especially in the presence of coarse particles with high specific gravity, such as hematite. In laboratory rotational rheometers (LRRs), entrance effects, particle settling, and Taylor vortices can jeopardize the accuracy of the results. This paper presents a new methodology for the rheological characterization of mineral slurries in tubular devices and the Principle of Maximum Entropy (PME) supports this new approach. Iron ore slurries were prepared at mass concentrations of 36.8% and 43.6% solids and subjected to rheological characterization in LRR and a pumping loop tubular device (PLTD). The results from LRR revealed shear-thickening behavior for the slurries; whereas the results from PLTD, associated with entropic equations for the friction factor and shear rate, revealed shear-thinning behavior (at low shear rates) and shear-thickening behavior (at high rates). The results from LRR plus PLTD were plotted in a single rheogram, and curve fitting was accomplished by the power law model (R²=0.995), indicating an overall shear-thickening behavior. PME proved to be capable of supporting the rheological characterization of mineral slurries at shear rates above 1500s^–1 in PLTD, complementing the results obtained by LRR.

Particle engineering broadly refers to the controlled production of drug particles optimized for size, morphology, and structure. It encompasses both destructive (top-down) and constructive (bottom-up) particle formation processes, of which the most used for commercial dry powder inhaler products are milling and spray drying. In both cases, undesirable physicochemical changes may occur because of thermal and mechanical stresses and through interactions with solvents, and can be further potentiated through storage and interaction with atmospheric water. The occurrence and extent of these phenomena are dependent upon the process parameters and the starting material, which necessitates a thorough understanding of these factors to create a stable product with the necessary characteristics for lung deposition. This review covers commonly arising issues in particle engineering and mechanisms of prevention. Topics to be discussed relating to physical changes include (1) the unintended generation of crystalline disorder and amorphous regions in particles; (2) polymorphic transformations; (3) unintended crystallization when amorphization is desired; and (3) triboelectric charging. Topics to be discussed relating to chemical changes include (1) thermal and mechanically activated chemical reactions; and (2) crystalline disorder and chemical reactivity.

Numerical modelling offers the opportunity to better understand, predict, and optimise the behaviours of industrial systems, and thus provides a powerful means of improving efficiency, productivity and sustainability. However, the accurate modelling of industrial-scale particulate and particle–fluid systems is, due to the complex nature of such systems, highly challenging. This challenge arises primarily from three factors: the lack of a universally accepted continuum model for particulate media; the computational expense of discrete particle simulations; and the difficulty of imaging industrial-scale systems to obtain validation data. In recent years, however, advances in software, hardware, theoretical understanding, and imaging technology have all combined to the point where, in many cases, these challenges are now surmountable—though some distance remains to be travelled. In this review paper, we provide an overview of the most promising solutions to the issues highlighted above, discussing also the major strengths and limitations of each.

The presence of organic dyes from industrial effluents has caused growing environmental and human health concerns. Various remediation methods and materials are available to minimize the environmental impact and ensure safe drinking water. Nitride composite particles have recently emerged as one of the promising materials for the efficient and selective removal of toxic and hazardous substances (including organic and inorganic compounds) from industrial wastewater. This review summarizes recent advances in the disposal of organic dyed wastewater using advanced nitride composite particles, including graphitic carbon nitride-based nanocomposites, boron nitride composites, and two-dimensional transition metal nitrides. The selection of appropriate materials remains largely a trial-and-error approach at present. This review highlights multiple dye-removal mechanisms, such as photocatalytic degradation, dye-sorption behavior, and computational analysis, to aid the material selection and shed light on the interactions between organic dye contaminants and nitride composites.

In several industrial units and applications, particulate solids are exposed to peculiar process conditions that significantly affect their flowability. Accurate characterisation and prediction of these effects are crucial for proper design and operation control of the processes. Liquid content, environmental humidity, and temperature can directly modify the type and magnitude of the interparticle forces and, thus, the cohesive behaviour at the bulk scale. This paper reports a critical review of experimental and modelling studies regarding the quantitative assessment of the effect of powder liquid content, environmental gas humidity and temperature on the mechanics of dense particle assemblies. Particular attention is paid to novel setups and experimental protocols that aim to go beyond the limits of standard and commercial instruments. A multiscale approach is followed from the particle level to the bulk level.

Fine particles are widely used as intermediate and final products in industrial processes. Because particle properties are directly linked to the function and quality of the products, synthesizing monodispersed particles is a key technology. A microreactor, which comprises microchannels typically narrower than 1 mm, is a promising reaction tool because it offers excellent mixing and heat transfer performance. We used a microreactor for the synthesis of single-component and composite nanoparticles. This review introduces our synthetic results for functional nanoparticles including nickel, platinum–cobalt alloys, gold and silver nanoshells, patchy particles, core–shell clusters, and metal–organic frameworks. The microreactor we used is of the central-collision type and exhibits a characteristic mixing time 100~1,000 times shorter than that of the conventional batch mixing. The excellent mixing ability of the microreactor enables the synthesis of monodisperse particles in size and shape as well as core–shell particles with uniform shell thickness through instantaneous nucleation. More importantly, the microreactor realizes syntheses, which are not possible with batch reactors, by trapping reaction intermediates in a sequential reaction process and by rapidly changing the reaction temperature. These results demonstrate great advantages of using the microreactor for nanoparticle synthesis.

Custom-made nanomaterials are indispensable in the production of high-value goods in almost any industry. For many applications, materials with defined functional contacts on the nanoscale between different components are crucial. In heterogeneous catalysis, active nanoparticles are often dispersed on a support, and defined interfaces facilitate the stabilization of the active materials. This leads to strong metal-support interactions (SMSI), which determine the activity and selectivity of the catalytic reactions. In photocatalysts, hetero-contacts can significantly reduce electron–hole recombination after light excitation, leading to improved photoefficiency. By choosing materials with appropriate band levels, the redox window can be tuned for a specific reaction. In batteries, mixing the active material and carbon leads to improved electrochemical characteristics. All these applications have in common that different nanomaterials need to be mixed at the nano-level with defined interfaces. This review highlights the most suitable routes for gas-phase synthesis of particle heteroaggregates, their modeling, and their applications.

The COVID-19 pandemic has underscored the importance of wearing effective facepiece filtering respirators (FFRs) to reduce infection and disease transmission. One of the reasons causing the widespread prevalence was found to be the failure of N95-Equivalent FFRs (N95-EFs), i.e., efficiency <<95%, during the pandemic. To investigate the reasons causing the ineffectiveness of commercial N95-EFs, this study measured the efficiency of several dozens of commercially available N95-EFs following standard testing protocols. The specifications of the N95-EF including fiber diameter, solidity and surface potential of the main layer media of N95-EFs were also determined. We provide a simple method for manufacturers to quickly screen the efficiencies of their N95-EF products before distributing them to the market. We found that the failures of N95-EF are majorly attributed to overprediction of the efficiency due to i) missing neutralization of challenging particles, ii) too small or oversize of challenging particles, and iii) particle detectors with large sizing limits (>500nm). Based on the pressure drop, respirator area, and surface potential of the N95-EFs, an empirical equation is developed to fast screen and help design effective N95-EFs.

Chemical mechanical polishing (CMP) is a process that uses mechanical abrasive particles and chemical interaction in slurry to remove materials from the surface of films. With advancements in semiconductor device technology applying various materials and structures, SiO₂ (silica) nanoparticles are the most chosen abrasives in CMP slurries. Therefore, understanding and developing silica nanoparticles are crucial for achieving CMP performance, such as removal rates, selectivity, decreasing defects, and high uniformity and flatness. However, despite the abundance of reviews on silica nanoparticles, there is a notable gap in the literature addressing their role as abrasives in CMP slurries. This review offers an in-depth exploration of silica nanoparticle synthesis and modification methods detailing their impact on nanoparticles characteristics and CMP performance. Further, we also address the unique properties of silica nanoparticles, such as hardness, size distribution, and surface properties, and the significant contribution of silica nanoparticles to CMP results. This review is expected to interest researchers and practitioners in semiconductor manufacturing and materials science.