Results from particle-resolved Direct numerical simulations are presented for dense suspensions of frictional non-colloidal spheres in viscous pressure-driven channel flow. The bulk solid volume fraction varies between ϕ_b=0.2 and 0.6, and the Coulomb friction coefficient is either μ_c=0 or 0.5. The main objectives are to unravel the influence of (1) ϕ_b and μ_c on the flow development time and of (2) heterogeneous shear on the steady-state suspension rheology. Starting from an initially homogeneous distribution, the particles show shear-induced migration toward the core until equilibrium is reached. The flow development time decays exponentially with increasing ϕ_b/Φ_R, where Φ_R is a friction-dependent reference bulk concentration beyond which particle contacts cause a rapid increase in the particle stress. The steady-state rheology is studied by means of the ‘viscous’ and ‘frictional’ rheology frameworks. Excluding the central core and wall regions, the data for the local relative suspension viscosity collapse onto a single curve as function of the normalized local concentration ϕ¯/ϕ_m, where ϕ_m is the friction-dependent maximum flowable packing fraction. The frictional rheology shows ‘subyielding’ at low viscous number I_v in the core region, where the macroscopic friction coefficient μ drops below the minimal value found for homogeneous shear flows. A modified frictional rheology model is presented that captures subyielding. Finally, a model is presented for ϕ¯/ϕ_mp as function of I_v, where ϕ_mp is a modified maximum flowable packing fraction. It captures both ‘overcompaction’ in the core beyond ϕ_m at high ϕ_b and maximum core concentrations below ϕ_m at lower ϕ_b.

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Non-photochemical laser-induced nucleation (NPLIN) has emerged as a promising primary nucleation control technique offering spatiotemporal control over crystallization with potential for polymorph control. So far, NPLIN was mostly investigated in milliliter vials, through laborious manual counting of the crystallized vials by visual inspection. Microfluidics represents an alternative to acquiring automated and statistically reliable data. Thus we designed a droplet-based microfluidic platform capable of identifying the droplets with crystals emerging upon Nd:YAG laser irradiation using the deep learning method. In our experiments, we used supersaturated solutions of KCl in water, and the effect of laser intensity, wavelength (1064, 532, and 355 nm), solution supersaturation (S), solution filtration, and intentional doping with nanoparticles on the nucleation probability is quantified and compared to control cooling crystallization experiments. Ability of dielectric polarization and the nanoparticle heating mechanisms proposed for NPLIN to explain the acquired results is tested. Solutions with lower supersaturation (S = 1.05) exhibit significantly higher NPLIN probabilities than those in the control experiments for all laser wavelengths above a threshold intensity (50 MW/cm²). At higher supersaturation studied (S = 1.10), irradiation was already effective at lower laser intensities (10 MW/cm²). No significant wavelength effect was observed besides irradiation with 355 nm light at higher laser intensities (≥50 MW/cm²). Solution filtration and intentional doping experiments showed that nanoimpurities might play a significant role in explaining NPLIN phenomena.

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Herein, we study the influences of the laser-exposed volume and the irradiation position on the nonphotochemical laser-induced nucleation (NPLIN) of supersaturated potassium chloride solutions in water. The effect of the exposed volume on the NPLIN probability was studied by exposing distinct milliliter-scale volumes of aqueous potassium chloride solutions stored in vials at two different supersaturations (1.034 and 1.050) and laser intensities (10 and 23 MW/cm²). Higher NPLIN probabilities were observed with increasing laser-exposed volume as well as with increasing supersaturation and laser intensity. The measured NPLIN probabilities at different exposed volumes are questioned in the context of the dielectric polarization mechanism and classical nucleation theory. No significant change in the NPLIN probability was observed when samples were irradiated at the bottom, top, or middle of the vial. However, a significant increase in the nucleation probability was observed upon irradiation through the solution meniscus. We discuss these results in terms of mechanisms proposed for NPLIN.

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The increasing prevalence of urolithiasis in industrialized societies triggered considerable interest in how various species found in urine regulate the nucleation and growth of common kidney stone constituents such as calcium oxalate (CaOx). Yet, the role macromolecules play in kidney stone formation is often overlooked due to their low concentration in urine. In this study, we investigate the nucleation kinetics of CaOx in artificial urine with droplet-based microfluidic induction time measurements at varying concentrations of oxalate and hyaluronic acid (HA), a polysaccharide commonly found in urine. The formation of two pseudo-polymorphic forms of calcium oxalate crystals, calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD), are carefully monitored using polarized light microscopy in induction time experiments. COM and COD nucleated concomitantly in artificial urine yet with distinct kinetics. Our results indicate that higher oxalate concentrations favor the formation of COD, the metastable form, over COM, the most stable form. Moreover, COD is also the fastest nucleating form in droplets under studied conditions. Furthermore, increasing the concentration of HA at fixed calcium and oxalate concentrations favored the nucleation of COM. We observed that in droplets where COM nucleated first, COD was not formed within the experimental time scale. However, in the droplets where COD appeared first, COM crystals were also observed later. We hope our findings shed light on the role macromolecules such as HA plays in dictating the pseudo-polymorphic form of CaOx and guide next generation treatments.@en

Nonphotochemical laser-induced nucleation (NPLIN) is a promising primary nucleation control method, yet its underlying mechanism remains elusive. To contribute to the discussion on whether the polarization of laser irradiation in NPLIN experiments influences the polymorphic outcome, we revisit NPLIN experiments with aqueous glycine solutions with supersaturations ranging between S = 1.5 and S = 1.7 irradiated by nanosecond pulses (∼7 ns) of near-infrared wavelength (1064 nm). Systematically altering laser light excitation properties, including the number of pulses and type of polarization, we quantified the nucleation kinetics and characterized the polymorphic form that crystallized upon laser irradiation. Due to the stochasticity of the nucleation process, a large number of samples (>100 per each experimental point) were studied under carefully controlled experimental conditions such as the ambient temperature, cooling rate, and aging period. We observed significant differences among laser-irradiated, spontaneously nucleated, and crash-cooled samples in terms of nucleation kinetics and polymorphic form. This result indicates that laser irradiation provides a different polymorph-forming pathway in comparison to crash-cooling and spontaneous nucleation. However, no clear dependence between the polymorphic form and the polarization of laser irradiation is observed. We discuss our results in the context of previous reports supported thorough quantification of sample heating in NPLIN experiments.

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A droplet-based microfluidic platform is presented to study the nucleation kinetics of calcium oxalate monohydrate (COM), the most common constituent of kidney stones, while carefully monitoring the pseudo-polymorphic transitions. The precipitation kinetics of COM is studied as a function of supersaturation and pH as well as in the presence of inhibitors of stone formation, magnesium ions (Mg2+), and osteopontin (OPN). We rationalize the trends observed in the measured nucleation rates leveraging a solution chemistry model validated using isothermal solubility measurements. In equimolar calcium and oxalate ion concentrations with different buffer solutions, dramatically slower kinetics is observed at pH 6.0 compared to pHs 3.6 and 8.6. The addition of both Mg2+ and OPN to the solution slows down kinetics appreciably. Interestingly, complete nucleation inhibition is observed at significantly lower OPN, namely, 3.2 × 10-8 M, than Mg2+ concentrations, 0.875 × 10-4 M. The observed inhibition effect of OPN emphasizes the often-overlooked role of macromolecules on COM nucleation due to their low concentration presence in urine. Moreover, analysis of growth rates calculated from observed lag times suggests that inhibition in the presence of Mg2+ cannot be explained solely on altered supersaturation. The presented study highlights the potential of microfluidics in overcoming a major challenge in nephrolithiasis research, the overwhelming physiochemical complexity of urine.

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In this comparative study, a solid composite, AN/HTPB-based propellant was prepared by conventional processing in a mechanical mixer and by applying an advanced processing technique relying on resonant acoustic mixing (RAM). After curing of the propellants, cross-sections were prepared and characterized by scanning electron microscopy. Also the density of the propellants was measured and finally the ballistic properties were measured using chimney burner tests. The experimental results clearly showed that the oxidizer particles, the homogeneity of the propellants, the density and the burn rate properties are hardly affected by the processing method. For the propellant studied in this research, resonant acoustic mixing is a very promising, advanced processing technique that can be applied as an alternative to the conventional mechanical mixing of this high solid load propellant composition.

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Accurate Calcium Oxalate Monohydrate (COM) solubility measurements are essential for elucidating the physiochemical mechanism behind the formation of kidney stones, nephrolithiasis. Yet the reported solubility values of COM in ultrapure water, arguably the simplest solvent relevant for nephrolithiasis, vary significantly depending on implemented method. To address this variation, we present an experimental study of the solubility of COM validated by a model based on the Debye–Hückel theory describing the solution chemistry and the complex formation. We also carefully monitor potential pseudopolymorphic/hydrate transitions during the solubility measurements with in-situ and ex-situ methods. Our results indicate that the solubility of COM in ultrapure water is a weak function of temperature. However, the measured solubility varies significantly in buffer solutions across physiologically relevant pH values at body temperature. The proposed model explains observed trends as a combined effect of ionic strength, protonation reactions, and soluble complex formation. Moreover, it predicts solubility of COM in buffer solutions remarkably well using our measurements in ultrapure water as input, demonstrating the consistency of presented approach. The presented study parleying experiments and modelling provides a solid stepping stone to extend the physiochemical understanding of nephrolithiasis to more realistic solutions laden with biological complexity.@en

In the domain of energetic nanomaterials, more specifically nano-sized explosives and oxidizers, many small scale production methods have been explored up to now. So far only limited attempts have been made to scale up the production to tens or maximally a few hunderds of grams. This paper provides a review of these small scale production methods as well as characterization techniques for nanometric explosives and oxidizers. As a result of the limited scale-up, the application of energetic nanomaterials in typical propellant and explosive formulations is currently very limited. This might be caused by the fact that a clear and commonly shared view on which energetic nanomaterials and production processes it would be economically beneficial and feasible to invest in is lacking at the moment. Furthermore, a considerable number of technical challenges can be expected regarding the processing of energetic nanomaterials on a composition level. To manage these challenges, this review proposes several technical solutions which may contribute to a better understanding of the benefits, risks and costs involved in the use and scale-up of energetic nanomaterials and, if considered economically feasible, a more widespread application of these nanomaterials in the defense and space domains.

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The aim of this paper is to produce spherical encapsulates of wheat gluten in a food-grade biopolymer for preparing sheared meat analogs, to prevent instant fibrilization of the gluten during a pre-mixing step. The hydrogel should release the gluten inside the Couette Cell, as a result of the higher temperature and shear in the process. Both sodium alginate and κ-carrageenan were used as encapsulants. Spherical particles of hydrogel-gluten mixtures were produced by means of a dripping method using an encapsulator. While the particle properties of κ-carrageenan surpassed those of alginate in terms of controlled release of the core, the particle production using the encapsulator was more complicated. With κ-carrageenan, a layer of oil on top of the cross-linking bath fluid, as well as through the outer orifice of a concentric nozzle were required to obtain a good sphericity of the particles. For the alginate particles the use of oil was not necessary. Gluten loadings of 7% w/w were achieved with 1.5% w/w alginate and with 2% w/w κ-carrageenan. The water content of the particles can be easily controlled by a subsequent partial drying step. A mixture of Soy Protein Isolate and particles was sheared in the Couette Cell. Controlled release of the gluten from the alginate particles was not achieved properly by temperature or shear. The controlled release of the gluten was achieved at the processing conditions only with κ-carrageenan. Some fibrilization was observed in the sheared product, but the macrostructure was not yet well developed. However, an optimization of the shearing process for the use of the particles may lead to an improved structure for the meat analogs.@en

A tensile module system placed within a Scanning Electron Microscope (SEM) was utilized to conduct in-situ tensile testing of propellant samples. The tensile module system allows for real-time in-situ SEM analysis of the samples to determine the failure mechanism of the propellant material under tensile force. The focus of this study was to vary the experimental parameters of the tensile module system and analyze how they affect the failure mechanism of the samples. The experimental parameters varied included strain rate and sample temperature (-54, +25 and +40°C). Stress-strain diagrams were recorded during the in-situ tensile tests, and these results were coupled with the in-situ images and videos of the samples captured with SEM analysis. The experiments conducted at -54°C showed a different failure behavior of the propellant sample due to its rigidity at this low temperature, while experiments conducted at +25 and +40°C displayed a similar failure mechanism. For future testing using this tensile tester, special attention should be given to improved temperature control of the specimen, especially at low temperatures.

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The failure mechanism of a propellant consisting of hydroxyl terminated poly-butadiene filled with ammonium perchlorate and aluminum (HTPB/AP/Al) was determined by performing in-situ uniaxial tensile tests in a scanning electron microscope (SEM). The experimental test plan contained uniaxial tensile test experiments performed at room temperature (25 °C) at three different strain rates (30, 150 and 750 μm min⁻¹). The in-situ images and in-situ videos collected by the SEM were correlated with the stress-strain diagrams created with the tensile experiments, in order to relate the failure mechanism to the features found in the stress-strain diagram. No significant strain rate dependency of the failure mechanism was observed when working with strain rates up to 750 μm min⁻¹ and working at room temperature. The stress-strain diagram showed indications of existing cracks and voids opening up prior to the creation of new cracks and/or voids in the sample, debonding of binder with AP particles as well as nucleation and coalescence of voids. On the fracture surfaces of the samples, it was apparent that the binder cleanly separated from the large AP particles but had a better bond with the aluminum particles. However, a difference in the appearance of a short drawing phase in the stress-strain diagram of the propellant is observed at different strain rates. The presented results clearly demonstrate the major advantage of the combination of microscopic tensile tests with microscopic observations, linking the stress-strain behavior to the mechanical deformation processes taking place in these propellant samples at the microscopic level.

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Studying links between triacetone triperoxide (TATP) samples from crime scenes and suspects can assist in criminal investigations. Isotope ratio mass spectrometry (IRMS) and gas chromatography (GC)-IRMS were used to measure the isotopic compositions of TATP and its precursors acetone and hydrogen peroxide. In total, 31 TATP samples were synthesized with different raw material combinations and reaction conditions. For carbon, a good differentiation and a linear relationship were observed for acetone–TATP combinations. The extent of negative (δ¹³C) fractionation depended on the reaction yield. Limited enrichment was observed for the hydrogen isotope (δ²H) values of the TATP samples probably due to a constant exchange of hydrogen atoms in aqueous solution. For oxygen (δ¹⁸O), the small isotopic range and excess of water in hydrogen peroxide resulted in poor differentiation. GC-IRMS and IRMS data were comparable except for one TATP sample prepared with high acid concentration demonstrating the potential of compound-specific isotope analysis. Carbon IRMS has practical use in forensic TATP investigations.

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In an attempt to further contribute to the characterization of explosive compositions, small scale Floret tests were performed using four RDX grades, differing in product quality. A Floret test provides a measure - by indentation of a copper block - of detonation spreading or the initiability and shock wave divergence and is applied in particular to explosives used in initiation trains. Both as-received RDX and PBXs (based on the AFX-757 composition, a hard target penetrator explosive) containing these RDX grades were tested in the Floret test set-up. It was found that the Floret test method, when applied to granular, as-received RDX, was not able to discriminate between the overall RDX product qualities on the basis of the resulting volume of the indentation in the copper block. For the Floret test data of the PBX samples, a division into two parts, where one of the RDX lots shows a lower dent volume compared to the other RDX lots tested. Based on the results presented in this paper with granular RDX and a PBX composition and earlier results with a different type of PBX (based on PBXN-109, an insensitive high explosive used in a wide range of munitions), the Floret test could be developed into a screening test for shock sensitivity and product quality, without the need for complex and large volume casting of specific PBX compositions.

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When applied to a pure component suspension in an apolar solvent, a strong inhomogeneous electric field induces particle movement, and the particles are collected at the surface of one of the two electrodes. This new phenomenon was used to separately isolate two organic crystalline compounds, phenazine and caffeine, from their suspension in 1,4-dioxane. First, crystals of both compounds were collected at different electrodes under the influence of an electric field. Subsequent cooling crystallization enabled the immobilization and growth of the particles on the electrodes, which were separately collected after the experiment with purities greater than 91%. This method can be further developed into a technique for crystal separation and recovery in complex multicomponent suspensions of industrial processes.@en

An explosive composition, derived from AFX-757, was systematically varied by using three different qualities of Class I RDX. The effect of internal defect structure of the RDX crystal on the shock sensitivity of a polymer bonded explosive is generally accepted (Doherty and Watt, 2008). Here the response to a mechanical non-shock stimulus is studied using an explosion-driven deformation test as well as the ballistic impact chamber. No correlation between RDX crystal quality and deformation sensitivity is observed. The DDT behavior (Deflagration to Detonation Transition) of the three plastic bonded explosives, although similar in composition, is distinct regarding the rate of diameter increase in the explosion-driven deformation test. Recovered polymer bonded explosive from the explosion-driven deformation test responds equally fast or slower in the ballistic impact chamber. Based on our experimental results the shear rate threshold as a single parameter describing mechanical sensitivity is challenged, and preference is given to the development of an ignition criterion based on inter-granular sliding friction under the action of a normal pressure.

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The influence of an explosion-driven deformation on the defect structure in RDX crystals embedded in a polymer-bonded explosive was investigated by means of confocal scanning laser microscopy. The images were compared to the defect structure in the as-received RDX grades, embedded in an epoxy resin. In this way it is possible to qualitatively analyze the changes in defect structure of the RDX crystals that were induced by the explosion-driven deformation. For the first time, these data therefore provide experimental confirmation of how shock waves mechanically interact with energetic crystals – a topic that, up to now, was only explored by means of simulations.@en