Individual Particle Level Research Articles

Statistical physics-based model of mechanical degradation in lithium ion batteries

The article presents a statistical model of mechanical degradation in the negative electrode of lithium ion batteries. During battery operation, nano-cracks nucleate and grow caused by the impact of diffusion-induced stress during Li-ion intercalation. Particle agglomeration is another mechanical effect that contributes to morphological changes. The presented model employs a population balance formalism to describe the propagation of the particle density distribution function in the electrode. A set of kinetic and transport equations accounts for structure-transforming processes at the level of individual particles. These processes alter the particle density distribution function, and cause changes in battery performance. A parametric study reveals the population of small particles and the width of the initial particle size distribution (PSD) as the main parameters that determine changes in electrochemical performance and capacity fade. The model is applied to experimental data in order to isolate and quantify the impact of various degradation mechanisms.

Towards quantitative prediction of the performance of dry powder inhalers by multi-scale simulations and experiments

This work demonstrates the use of multi-scale simulations coupled with experiments to build a quantitative prediction tool for the performance of adhesive mixtures in a dry powder inhaler (DPI). Using discrete element model (DEM), the behaviour of fine-carrier particle assemblies upon different mechanisms encountered during dose entrainment and dispersion can be described at the individual particle level. Combining these results with computational fluid dynamics (CFD) simulations, the complete dosing event from a DPI can be captured and key performance measures can be extracted. A concept of apparent surface energy, ASE, was introduced to overcome challenges associated with the complex particle properties, e.g. irregular particle shapes and surface roughness. This approach correctly predicts trends observed experimentally regarding API adhesivity, flow rate and device geometry. By incorporating the effects of drug load, critical adhesion and surface energy distributions to the simulation tool, the fine particle fraction could be predicted with good agreement to experiments for two different formulations in two different devices at two flow rates. It is concluded that multi-scale simulations provide a useful tool to support device and formulation development, as well as to gain further insight into the physical mechanisms governing dispersion from DPIs.

Experimental investigation of variations in morphology, composition and mixing-state of boundary layer aerosol: A balloon based study over urban environment (New Delhi)

The morphology, composition, and complex mixing states of aerosol are extremely important physico-chemical properties which are the major inputs to the optical/radiative models. Though, ground based observations of the said properties are abundant but the vertical profiles of the same are very much limited throughout the globe. The information on the vertical heterogeneity of the aforementioned properties over a polluted environment like Delhi will be very helpful to develop a better understanding of the thermodynamics of the lower atmosphere.In present study, we carried out a tethered balloon based field campaign in National Physical Laboratory (28° 38′ 10″ N, 77° 10′ 17″ E) from 21 to 27 February 2014 to explore the vertical distribution of the said properties. Based on the microscopic observations, the bubbly shaped sulfate particles number percentage is less (5%) on the ground, abundant (49%) on altitude <350 m and nearly absent on altitude >350 m. At 500 m altitude, particles were majorly of spiked shape with elongated dimension ∼ 3–4 μm. The number percentage of the aged fractals has been found to increase by 4% in the 100–350 m range against the ground observations. Based on the bulk composition of non-carbonaceous species, at 200 m altitude, we observed significant amount (74%) of the oxides of sulfur compared to that of ground observations (30%) that could be due to temperature inversion and air parcel movement from IGP (Indo Gangetic Plain). Various core-shell type particle configurations have been observed at different altitudes. At 200 m altitude, particles were majorly aged with anionic species (like S, Cl and HSO4) and cationic species (like C2H5). The bulk and individual particle level data generated over Delhi environment in this experiment may improve our understanding of boundary layer aerosol and could provide the scientific insights of their probable effects on low level cloud formation.

Development of a SEM-based low-energy in-line electron holography microscope for individual particle imaging

A new SEM-based in-line electron holography microscope has been under development. The microscope utilizes conventional SEM and BF-STEM functionality to allow for rapid searching of the specimen of interest, seamless interchange between SEM, BF-STEM and holographic imaging modes, and makes use of coherent low-energy in-line electron holography to obtain low-dose, high-contrast images of light element materials. We report here an overview of the instrumentation and first experimental results on gold nano-particles and carbon nano-fibers for system performance tests. Reconstructed images obtained from the holographic imaging mode of the new microscope show substantial image contrast and resolution compared to those acquired by SEM and BF-STEM modes, demonstrating the feasibility of high-contrast imaging via low-energy in-line electron holography. The prospect of utilizing the new microscope to image purified biological specimens at the individual particle level is discussed and electron optical issues and challenges to further improve resolution and contrast are considered.

3D mapping of nanoscale crosslink heterogeneities in microgels.

The majority of swollen polymer networks exhibit spatial variations in crosslink density. These spatial heterogeneities are particularly important in colloidal gel particles, or microgels, where they manifest themselves on the nanoscale and impact mechanical and transport properties. Despite their importance, the real space nanostructure of these heterogeneities at the individual particle level has remained elusive. Using state of the art super-resolution microscopy known as Whole cell 4Pi Single Molecule Switching Nanoscopy (W-4PiSMSN) we demonstrate 3D nanoscale mapping of spatial crosslink heterogeneities in a model system of poly(N-isopropylacrylamide) colloidal gel particles containing a novel fluorophore tagged crosslinker. We reveal the presence of higher crosslink density clusters embedded in a lower crosslink density matrix within the core of individual microgel particles, a phenomenon that has been predicted, but never been observed before in real space. The morphology of the clusters provides insight into the kinetics of microgel formation. This study also provides proof-of-concept 3D super-resolution imaging of spatial heterogeneities in bulk hydrogels.

Intrinsic Size Effect in Scaffolded Porous Calcium Silicate Particles and Mechanical Behavior of Their Self-Assembled Ensembles.

Scaffolded porous submicron particles with well-defined diameter, shape, and pore size have profound impacts on drug delivery, bone-tissue replacement, catalysis, sensors, photonic crystals, and self-healing materials. However, understanding the interplay between pore size, particle size, and mechanical properties of such ultrafine particles, especially at the level of individual particles and their ensemble states, is a challenge. Herein, we focus on porous calcium-silicate submicron particles with various diameters-as a model system-and perform extensive 900+ nanoindentations to completely map out their mechanical properties at three distinct structural forms from individual submicron particles to self-assembled ensembles to pressure-induced assembled arrays. Our results demonstrate a notable "intrinsic size effect" for individual porous submicron particles around ∼200-500 nm, induced by the ratio of particle characteristic diameter to pore characteristic size distribution. Increasing this ratio results in a brittle-to-ductile transition where the toughness of the submicron particles increases by 120%. This size effect becomes negligible as the porous particles form superstructures. Nevertheless, the self-assembled arrays collectively exhibit increasing elastic modulus as a function of applied forces, while pressure-induced compacted arrays exhibit no size effect. This study will impact tuning properties of individual scaffolded porous particles and can have implications on self-assembled superstructures exploiting porosity and particle size to impart new functionalities.

Effect of crystallinity on droplet regression and disruptive burning characteristics of nanofuel droplets containing amorphous and crystalline boron nanoparticles

The present investigation deals with the droplet combustion characteristics of nanofuel droplets containing amorphous and crystalline boron nanoparticles at various particle loadings (0.25%, 1%, 2.5%, 5%, 7.5%, and 10% by weight). Characterization of pre-burnt particles in terms of particle size, morphology, and elemental boron content have been carried out using standard material characterization techniques such as SEM, TEM, XRD and TGA. The droplet burning process has been recorded using a high-speed imaging system. The diameter regression profiles show distinctly different characteristics for amorphous and crystalline particles loaded droplets. Amorphous particles loaded droplets show comparatively smooth regression with minor puffing coupled with shape oscillations at the early stage and micro-explosions at the later stage whereas the crystalline particles loaded droplets show sudden ejections and high-intensity micro-explosions. The morphology of the particle (crystallinity) is considered to be responsible for this difference in burning behaviour. A porous, permeable agglomerate shell forms in case of amorphous boron loaded droplet whereas a densely packed, impermeable agglomerate shell forms in case of crystalline boron loaded droplets during the early stage of burning. The micrographs of post-burning residues indeed reveal that blow holes are present in the agglomerate even at individual particle level for amorphous boron loaded case whereas there are no such blow holes present in crystalline boron loaded case. Thermograms, true colour images of flame and emission spectra show that the amorphous boron particles burn better than their crystalline counterpart.

Molecular identification of polymers and anthropogenic particles extracted from oceanic water and fish stomach - A Raman micro-spectroscopy study.

Pacific Ocean trawl samples, stomach contents of laboratory-raised fish as well as fish from the subtropical gyres were analyzed by Raman micro-spectroscopy (RMS) to identify polymer residues and any detectable persistent organic pollutants (POP). The goal was to access specific molecular information at the individual particle level in order to identify polymer debris in the natural environment. The identification process was aided by a laboratory generated automated fluorescence removal algorithm. Pacific Ocean trawl samples of plastic debris associated with fish collection sites were analyzed to determine the types of polymers commonly present. Subsequently, stomach contents of fish from these locations were analyzed for ingested polymer debris. Extraction of polymer debris from fish stomach using KOH versus ultrapure water were evaluated to determine the optimal method of extraction. Pulsed ultrasonic extraction in ultrapure water was determined to be the method of choice for extraction with minimal chemical intrusion. The Pacific Ocean trawl samples yielded primarily polyethylene (PE) and polypropylene (PP) particles >1mm, PE being the most prevalent type. Additional microplastic residues (1mm - 10μm) extracted by filtration, included a polystyrene (PS) particle in addition to PE and PP. Flame retardant, deca-BDE was tentatively identified on some of the PP trawl particles. Polymer residues were also extracted from the stomachs of Atlantic and Pacific Ocean fish. Two types of polymer related debris were identified in the Atlantic Ocean fish: (1) polymer fragments and (2) fragments with combined polymer and fatty acid signatures. In terms of polymer fragments, only PE and PP were detected in the fish stomachs from both locations. A variety of particles were extracted from oceanic fish as potential plastic pieces based on optical examination. However, subsequent RMS examination identified them as various non-plastic fragments, highlighting the importance of chemical analysis in distinguishing between polymer and non-polymer residues.

Triple Junction at the Triple Point Resolved on the Individual Particle Level.

At the triple point of a repulsive screened Coulomb system, a fcc crystal, a bcc crystal, and a fluid phase coexist. At their intersection, these three phases form a liquid groove, the triple junction. Using confocal microscopy, we resolve the triple junction on a single-particle level in a model system of charged PMMA colloids in a nonpolar solvent. The groove is found to be extremely deep and the incommensurate solid-solid interface to be very broad. Thermal fluctuations hence appear to dominate the solid-solid interface. This indicates a very low interfacial energy. The fcc-bcc interfacial energy is quantitatively determined based on Young's equation and, indeed, it is only about 1.3 times higher than the fcc-fluid interfacial energy close to the triple point.

Early cytoplasmic uncoating is associated with infectivity of HIV-1

After fusion, HIV delivers its conical capsid into the cytoplasm. To release the contained reverse-transcribing viral genome, the capsid must disassemble in a process termed uncoating. Defining the kinetics, dynamics, and cellular location of uncoating of virions leading to infection has been confounded by defective, noninfectious particles and the stochastic minefield blocking access to host DNA. We used live-cell fluorescent imaging of intravirion fluid phase markers to monitor HIV-1 uncoating at the individual particle level. We find that HIV-1 uncoating of particles leading to infection is a cytoplasmic process that occurs ∼30 min postfusion. Most, but not all, of the capsid protein is rapidly shed in tissue culture and primary target cells, independent of entry pathway. Extended time-lapse imaging with less than one virion per cell allows identification of infected cells by Gag-GFP expression and directly links individual particle behavior to infectivity, providing unprecedented insights into the biology of HIV infection.

One- and two-component colloidal glasses under transient shear

In concentrated colloidal mixtures different caging mechanisms exist and result in different arrested states: repulsive, attractive and asymmetric glasses as well as gel-like states. We discuss their microscopic structure, dynamics and rheological response. Special attention is given to the non-linear mechanical behaviour, in particular the transient rheological response after shear is started. Steps in both, shear rate and shear stress (creep test), are considered. The macroscopic viscoelastic response is related to the microscopic structure and dynamics on the individual-particle level.

Morphology, Mineralogy and Mixing of Individual Atmospheric Particles Over Kanpur (IGP): Relevance of Homogeneous Equivalent Sphere Approximation in Radiative Models

Estimation of the direct radiative forcing (DRF) by atmospheric particles is uncertain to a large extent owing to uncertainties in their morphology (shape and size), mixing states, and chemical composition. A region-specific database of the aforementioned physico-chemical properties (at individual particle level) is necessary to improve numerically-estimated optical and radiative properties. Till date, there is no detailed observation of the above mentioned properties over Kanpur in the Indo-Gangetic Plain (IGP). To fill this gap, an experiment was carried out at Kanpur (IITK; 26.52°N, 80.23°E, 142 m msl), India from April to July, 2011. Particle types broadly classified as (a) Cu-rich particles mixed with carbon and sulphur (b) dust and clays mixed with carbonaceous species (c) Fe-rich particles mixed with carbon and sulfur and (d) calcite (CaCO3) particles aged with nitrate, were observed. The frequency distributions of aspect ratio (AR; indicator of extent of particle non-sphericity) of total 708 particles from April to June reveal that particles with aspect ratio range >1.2 to ≤1.4 were abundant throughout the experiment except during June when it was found to shift to high AR range, >1.4 to ≤1.6 (followed with another peak of AR i.e. >2 to ≤2.4) due to dust storm conditions enhancing the occurrence of more non-spherical particles over the sampling site. The spherical particles (and close to spherical shape; AR range, 1.0 to ≤1.2) were found to be <20% throughout the experiment with a minimum (11.5%) during June. Consideration of Homogeneous Equivalent Sphere Approximation (HESA) in the optical/radiative model over the study region is found to be irrelevant during the campaign.

Enhancing the interpretation of in vitro bioaccessibility data by using computer controlled scanning electron microscopy (CCSEM) at the individual particle level

The adverse health effects resulting from exposure to contaminated soil on internally displaced populations in Mitrovica, Kosovo can be determined by how the potentially harmful elements are bound in the soils. Certainly this was the case for Pb, present at concentrations ranging from 624 to 46,900 mg/kg, and at bioaccessibilities ranging <5% to nearly 90%. To assess why the soil Pb might differ so markedly in terms of its bioaccessibility, computer controlled scanning electron microscopy (CCSEM) was employed to determine how the Pb was associated with other elements at the individual particle (IP) level in soils from the area. It was found that the Pb-bearing particle types were, for the most part, different in each sample. We consider these differences as the main control on Pb bioaccessibility in these soils. Pb solubility at the IP level was evaluated by examining Pb-particles from these soils in the electron microscope before and after successive immersions in a simulated gastric fluid. This analysis (differential IP analysis) confirmed the CCSEM characterization that Pb associated with other higher atomic number elements (Fe, Zn, Cu and Ni) was less soluble than when it was present as isolated phases (e.g., as carbonate) or when it was bound with lower atomic number elements (Na, Al, Si, K, Ca). The heterogeneity in solubility and composition of the Pb-particles suggested that the Pb originated from a range of different anthropogenic activities. The nature of these different anthropogenic activities created the wide differences in Pb-bioaccessibilty by producing Pb bound in many different forms in the soil particles. This type of Pb-particle characterization highlights the role CCSEM analysis, and IP acid extraction, can play in providing supporting evidence alongside bioaccessibility data for applications in human health risk assessment and management of contaminated soil.

Classification of microcrystalline celluloses via structures of individual particles measured by synchrotron radiation X-ray micro-computed tomography

Microcrystalline cellulose (MCC) is one of the most important excipients due to its outstanding binding and tableting properties. Owing to the absence of high resolution characterization techniques at the single particle scale, 3D (three dimension) microstructure of MCC and its effects on formulation performance remain unexamined. The aim of this work was to establish a methodology for single particles of MCC type 102 based on synchrotron radiation X-ray micro computed tomography (SR-μCT), principal component analysis (PCA) and partial least square discriminant analysis (PLSDA). Scanning electron microscopy, SR-μCT, powders properties together with tensile strength (TS), disintegration time (DT), Kawakita plots and force/displacement profiles of tablets were measured. PCA-PLSDA was applied to evaluate the structural classification of MCC particles on the basis of 2D and 3D SR-μCT derived images. The studied MCCs were found to differ in the TS, DT, Kawakita plot and force/displacement, while box ratio and Feret ratio had major influence on the principal components, but the angle of repose, bulk and tapped density did not exhibit significantly. These findings verified that different samples of MCCs from alternative suppliers have morphological diversity when assessed at the individual particle level, which could result into variation in powder properties and tableting performance.

Dealloying in Individual Nanoparticles and Thin Film Grains: A Bragg Coherent Diffractive Imaging Study

Dealloying is a process whereby selective dissolution results in a porous, strained structure often with new properties. The process is of both intrinsic and applied interest, and recently has been used to make highly active catalysts. The porosity has been studied using electron microscopy while the dealloying‐induced strain has been studied at the ensemble level using X‐ray diffraction. Despite the importance of local, for example, at the individual particle or grain level, strain in controlling the properties of the dealloyed material, it remains unresolved due to the difficulty of imaging 3D strain distributions with nanometer resolution in reactive environments. This information could play an integral role in understanding and controlling lattice strain for a variety of applications. Here, 3D strain distributions in individual nanoparticles and thin film grains in silver–gold alloys undergoing nitric acid‐induced dealloying are imaged by Bragg coherent diffractive imaging. Particles exhibit dramatic changes in their local strains due to dealloying but grains do not. The average lattice in both grains and particles contracts during dealloying. In general, the results reveal significant dealloying‐induced strain heterogeneity at the nanoscale in both isolated and extended samples, which may be utilized to develop advanced nanostructures for a variety of important applications.

In situ Visualization of State-of-Charge Heterogeneity within a LiCoO2 Particle that Evolves upon Cycling at Different Rates

For designing new battery systems with higher energy density and longer cycle life, it is important to understand the degradation mechanism of the electrode material, especially at the individual particle level. Using in situ transmission X-ray microscopy (TXM) coupled to a pouch cell setup, the inhomogeneous Li distribution as well as the formation, population, and evolution of inactive domains in a single LiCoO2 particle were visualized as it was cycled for many times. It is found that the percentage of the particle that fully recovered to the pristine state is strongly related to the cycling rate. Interestingly, we also observed the evolution of the inactive region within the particle during long-term cycling. The relationship between morphological degradation and chemical inhomogeneity, including the formation of unanticipated Co metal phase, is also observed. Our work highlights the capability of in situ TXM for studying the degradation mechanism of materials in LIBs.

GPU accelerated Discrete Element Method (DEM) molecular dynamics for conservative, faceted particle simulations

Faceted shapes, such as polyhedra, are commonly found in systems of nanoscale, colloidal, and granular particles. Many interesting physical phenomena, like crystal nucleation and growth, vacancy motion, and glassy dynamics are challenging to model in these systems because they require detailed dynamical information at the individual particle level. Within the granular materials community the Discrete Element Method has been used extensively to model systems of anisotropic particles under gravity, with friction. We provide an implementation of this method intended for simulation of hard, faceted nanoparticles, with a conservative Weeks–Chandler–Andersen (WCA) interparticle potential, coupled to a thermodynamic ensemble. This method is a natural extension of classical molecular dynamics and enables rigorous thermodynamic calculations for faceted particles.

Statistical Physics-Based Model of Solid Electrolyte Interphase Growth in Lithium Ion Batteries

The article presents a statistical physics-based model for the growth of the solid electrolyte interphase (SEI) in the negative electrode of lithium ion batteries. During battery operation, the SEI thickness grows by the reaction between lithium ions, electrons and solvent species on the surface of active particles at the negative electrode. The growth of the SEI layer causes a loss of lithium ions that induces capacity fade. In addition, it increases the ion transport resistance and decreases the total porosity. Our model employs a population balance formalism based on the Fokker-Planck Equation to describe the propagation of the particle density distribution function in the electrode. Structure-transforming processes at the level of individual particles are accounted for by using a set of kinetic and transport equations. These processes alter the particle density distribution function, and cause changes in battery performance. A parametric study of the model singles out the first moment of the initial SEI thickness distribution as the determining factor in predicting the capacity fade. The model-based treatment of experimental data allows analyzing processes that control SEI growth and extracting their controlling parameters.

A Snapshot of the Properties of Single Nanoparticles at the Moment of a Collision.

Direct electrochemical characterization of freely moving nanoparticles (NPs) at the individual particle level is challenging. A method is presented that can achieve this goal based on the collision between a NP and an ultramicroelectrode (UME). By applying a sinusoidal potential to the UME and monitoring the current response in the frequency domain, a sudden change in the phase angle indicates the arrival of a NP at the UME. The response induced by the collision can be isolated and used to explore the properties of the NP. This method, analogous to a high-speed camera, can obtain a snapshot of the properties of the single NP at the moment of a collision. The proposed method was employed to investigate the properties of both the hard catalytic Pt NP and soft electroactive emulsion droplets, and many new insights were revealed thereafter. The method also has the potential to be applied in many other fields, where the interested signals appear as discrete events.

Entropy at the Level of Individual Particles: Analysis of Maxwell’s Agent with a Hidden-Variable Theory

Problem: Maxwell’s Agent (MA) is a thought experiment about whether the second Law is violated at smaller scales. This is a complex problem because the scale dependencies are unclear for perfect gas assumptions, quantum coherence, thermalisation, and contextual measurement. Purpose: The MA is explored from a non-local hidden-variable (NLHV) perspective. Approach: The Cordus theory, a specific NLHV solution, was applied at macroscopic to fundamental scales. Physical realism requires the Agent be included in the analysis. Findings: The primary function is sorting, i.e. a one-time separation of species by some attribute. The thermodynamic MA situation is merely a special case for reducing disorder (entropy). A one-time extraction of energy is possible. This requires input energy, hence the device only has thermodynamic leverage and is not a perpetual motion device. Inefficiencies arise from thermalisation causing short mean free path of Brownian motion, perfect gases having minimal interaction with the gate, ambiguity about spatial location arising from quantum superposition, contextual measurement interfering with the particle velocity, and bremsstrahlung hysteresis losses occurring when the Agent operates. Implications: Entropy is a group property at the bulk level, not a characteristic of the individual particle, and can be reversed at an energy cost at the particle level. Originality: The explanation spans multiple levels from macroscopic down to fundamental, which is unusual. Achieving an explanation from the NLHV sector is novel. The theory accommodates superposition, irreversibility, entropy, contextual measurement, coherence-discord transition, and Brownian motion.