Particle Size Regime Research Articles

Particle size-dependent flexibility in DUT-8(Cu) pillared layer metal-organic framework.

The nature of metal in the isomorphous flexible metal-organic frameworks is often reported to influence flexibility and responsivity. A prominent example of such behaviour is the DUT-8(M) family ([M2(2,6-ndc)2(dabco)]n, 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane), where the isostructural compounds with Ni, Zn, Co, and Cu in the paddle wheel cluster are known. The macro-sized crystals of Ni, Co, and Zn based compounds transform to the closed pore (cp) phase under desolvation and show typical gate opening behaviour upon adsorption. The choice of metal, in this case, allows the adjustment of switching kinetics, selectivity in adsorption, and gate-opening pressures. The submicron-sized crystals of of Ni, Co, and Zn based compounds remain in the open pore (op) phase after desolvation. In this contribution, we demonstrate that the presence of Cu in the paddle wheel leads to fundamentally different flexible behaviour. The DUT-8(Cu) desolvation does not lead to the formation of the cp phase, independent of the particle size regime. However, according to in situ powder diffraction analysis, the desolvated, macro-sized crystals of DUT-8(Cu)_op show breathing upon adsorption of CO2 at 195 K. The submicron-sized particles show rigid, nonresponsive behaviour.

Substrate size modifies stream grazer-biofilm interactions in the presence of invertivorous fish.

When herbivore abundance is controlled by predators there may be an indirect positive effect on primary producers due to reduced grazing pressure, but the potential of predation refuges to modify such trophic cascades has rarely been studied. By experimentally manipulating substrate particle size and fish predation regime, we assessed the outcome of invertebrate grazer-biofilm interactions in streams. Locations at the center of larger substrate particles were predicted to pose a higher predation risk, and therefore be subjected to a lower grazing pressure. In our 52-day experiment in a New Zealand stream, small-sized substrates (terracotta tiles) remained virtually free of periphyton across their entire upper surface, whereas a thick periphyton mat was formed across large tiles with only edges remaining free. In channels containing fish (either native Galaxias vulgaris or exotic Salmo trutta), grazing on tiles was lower than in the absence of fish. A preference for grazing near to the edge of tiles was clearest in fish channels but was also evident even in the absence of fish, probably reflecting fish presence and/or fish kairomones in the stream from where the colonizing invertebrates had been derived. Total grazer density was similar across treatments with or without fish, suggesting that our results can be explained mostly by changes in the behavior of grazers. We suggest that refuge availability, interacting with grazer predator-avoidance behavior, may produce a context-dependent patchwork of trophic cascades in streams and other ecosystems.

Colloidal Polydopamine Beads: A Photothermally Active Support for Noble Metal Nanocatalysts

Polydopamine (PDA) is a unique bioinspired synthetic polymer that integrates broadband light absorption, efficient photothermal transduction, and versatile surface-adhesion functions in a single material entity. Here, we utilize colloidal PDA beads in the submicron particle size regime as an easily processable and photothermally active support for sub-10 nm Pd nanocatalysts to construct a multifunctional material system that allows us to kinetically boost thermal catalytic reactions through visible and near-infrared light illuminations. Choosing the Pd-catalyzed nitrophenol reduction by ammonium formate as a model transfer hydrogenation reaction exhibiting temperature-dependent reaction rates, we demonstrate that interfacial molecule-transforming processes on metal nanocatalyst surfaces can be kinetically modulated by harnessing the thermal energy produced through photothermal transduction in the PDA supports.

Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime

In many energy and combustion applications, particles experience large temperature gradients, which can affect the coagulation process due to thermophoresis. This study presents a rigorous theory of thermophoretically modified Brownian coagulation in the entire particle size regime. The theoretical derivations are based on the kinetic theory for the free-molecular regime and the harmonic mean method for the transition regime. The coagulation kernels in different size regimes can be expressed as the basic Brownian coagulation kernel times an enhancement factor. The enhancement factor represents the coagulation rate enhancement induced by thermophoresis and is a function of specific dimensionless numbers. Based on the enhancement factor, the thermophoretic enhancement effects on particle coagulation are further analyzed under a wide range of gas and particle conditions. The results show that thermophoretic enhancement effects are ignorable in the free-molecular regime, but need to be considered in the continuum regime and the transition regime. In addition, the enhancement effects increase significantly with increase of gas temperature and temperature gradient while decrease with increase of gas pressure. The present study can improve understanding of thermophoretic effects on Brownian coagulation in the entire size regime and provide a useful tool to calculate the coagulation rates in presence of thermophoresis.

Does Biochar Particle Size, Application Rate and Irrigation Regime Interact to Affect Soil Water Holding Capacity, Maize Growth and Nutrient Uptake?

Does Biochar Particle Size, Application Rate and Irrigation Regime Interact to Affect Soil Water Holding Capacity, Maize Growth and Nutrient Uptake?

Lagrangian particle tracking with new weighted fraction Monte Carlo method for studying the soot particle size distributions in premixed flames

PurposeThe purpose of this paper is to study the soot formation and evolution by using this newly developed Lagrangian particle tracking with weighted fraction Monte Carlo (LPT-WFMC) method.Design/methodology/approachThe weighted soot particles are used in this MC framework and is tracked using Lagrangian approach. A detailed soot model based on the LPT-WFMC method is used to study the soot formation and evolution in ethylene laminar premixed flames.FindingsThe LPT-WFMC method is validated by both experimental and numerical results of the direct simulation Monte Carlo (DSMC) and Multi-Monte Carlo (MMC) methods. Compared with DSMC and MMC methods, the stochastic error analysis shows this new LPT-WFMC method could further extend the particle size distributions (PSDs) and improve the accuracy for predicting soot PSDs at larger particle size regime.Originality/valueCompared with conventional weighted particle schemes, the weight distributions in LPT-WFMC method are adjustable by adopting different fraction functions. As a result, the number of numerical soot particles in each size interval could be also adjustable. The stochastic error of PSDs in larger particle size regime can also be minimized by increasing the number of numerical soot particles at larger size interval.

A Novel Calibration Method for the Quantification of Respirable Particles in Mining Scenarios Using Fourier Transform Infrared Spectroscopy.

The exposure of mining workers to crystalline particles, e.g., alpha quartz in respirable dust, is a ubiquitous global problem in occupational safety and health at surface and underground operations. The challenge of rapid in-field monitoring for direct assessment and adoption of intervention has not been solved satisfactorily to date, as conventional analytical methods such as X-ray diffraction and infrared spectroscopy require laboratory environments, complex system handling, tedious sample preparation, and are limited by, e.g., addressable particle size. A novel monitoring approach was developed for potential in-field application enabling the quantification of crystalline particles in the respirable regime based on transmission infrared spectroscopy. This on-site approach analyzes samples of dust in ambient air collected onto PVC filters using respirable dust sampling devices. In the present study, we demonstrate that portable Fourier transform infrared (FT-IR) spectroscopy in combination with multivariate data analysis provides a versatile tool for the identification and quantification of minerals in complex real-world matrices. Without further sample preparation, the loaded filters are immediately analyzed via transmission infrared spectroscopy, and the mineral amount is quantified in real-time using a partial least squares regression algorithm. Due to the inherent molecular selectivity for crystalline as well as organic matrix components, infrared spectroscopy uniquely allows to precisely determine the particle composition even in complex samples such as dust from coal mines or clay-rich environments. For establishing a robust partial least squares regression model, a method was developed for generating calibration samples representative in size and composition for respirable mine dust via aerodynamic size separation. Combined with experimental design strategies, this allows tailoring the calibration set to the demands of air quality management in underground mining scenarios, i.e., the respirable particle size regime and the matrix of the target analyte.

Structure, magnetism and electrical transport in La1-x-yPryCaxMnO3 (y = 0.30, 0.35, 0.40; x = 0.40): Consequences of the interplay between intrinsic ionic radius and extrinsic particle size

The structural, microstructural, magnetic and electrical transport properties have been correlatively studied to decipher the complex consequences of variation of intrinsic parameter ,the average La-site cationic radii and extrinsic particle size on the magneto-electrical phase coexistence in La1-x-yPryCaxMnO3 (y = 0.30, 0.35, 0.40; x = 0.40). Polycrystalline powders prepared by sol-gel route were sintered at 600 °C, 900 °C, 1100 °C, and 1300 °C to facilitate particle size variation. Rietveld refinement of the powder X-ray diffraction data confirms that all samples have an orthorhombic structure with Pnma space group. The lattice constants decrease with decreasing ionic radii, while at a fixed ionic radius, the enhanced particle size increases them. The average apical Mn−O−Mn bond angles and the average Mn−O bond lengths decrease with rising ionic radii but increase with particle size at a fixed composition. Magnetization measurements show sequential paramagnetic (PM)-antiferromagnetic (AFM)-ferromagnetic (FM) transitions on lowering the temperature is lowered. The AFM-FM transition exhibits (i) pronounced hysteresis between field-cooled cooling (FCC) and field-cooled warming (FCW) (ii) strong divergence between zero-field cooling (ZFC) and FCW curves. The low-temperature magnetic state transforms from spin glass-like to a cluster glass-like as the ionic radii or the particle size decreases. These behaviors are caused by the mesoscale modifications in the magnetic phase profile where the AFM and FM phases due to the interplay between the average La-site cationic radii and the particle size. In general, the FM component increases with an increase in the particle size, but it decreases at lower ionic radii. The presence of a large thermal hysteresis in the insulator-metal transition (IMT) coupled with the one in FCC-FCW magnetization at particle sizes ~200 nm–160 nm, and ~460-400 nm demonstrates that this particle size regime is the most conducive to the phase separation. IMT disappears at smaller ionic radii and larger particle sizes due to the enhancement of AFM and charge-ordering. The PM and AFM regimes in all samples reveal variable range hopping conduction with particle size and ionic radii dependent activation. The observed phenomena have been explained in terms of the interplay between the ionic radii and particle size induced changes in the average apical Mn−O−Mn bond angles and the average Mn−O bond length.

Microfluidic approaches for the production of monodisperse, superparamagnetic microspheres in the low micrometer size range

The preparation of small, monodispersed magnetic microparticles through microfluidic approaches has been consistently challenging due to the high energy input needed for droplet break-off at such small diameters. In this work, we show the microfluidic production of 1–3 μm magnetic nanoparticle-loaded poly(d, l-lactide) (PLA) microspheres. We describe the use of two approaches, using a conventional flow-focusing microfluidic geometry. The first approach is the separation of target size satellite particles from the main droplets; the second approach is the direct production using high flow rate jetting regimes. The particles were produced using a polymeric thiol-ene microfluidic chip platform, which affords the straightforward production of multiple chip copies for single-time use, due to large feature sizes and replica molding approaches. Through the encapsulation of magnetite/maghemite nanoparticles, and their characterization with scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) measurements, we show that the resulting particles are monosized, highly spherical and exhibit superparamagnetic properties. The particle size regime and their magnetic response show potential for in vivo intravenous applications of magnetic targeting with maximum magnetic response, but without blocking an organ’s capillaries.

Robust metric for quantifying the importance of stochastic effects on nanoparticle growth

Comprehensive representation of nanoparticle dynamics is necessary for understanding nucleation and growth phenomena. This is critical in atmospheric physics, as airborne particles formed from vapors have significant but highly uncertain effects on climate. While the vapor–particle mass exchange driving particle growth can be described by a macroscopic, continuous substance for large enough particles, the growth dynamics of the smallest nanoparticles involve stochastic fluctuations in particle size due to discrete molecular collision and decay processes. To date, there have been no generalizable methods for quantifying the particle size regime where the discrete effects become negligible and condensation models can be applied. By discrete simulations of sub-10 nm particle populations, we demonstrate the importance of stochastic effects in the nanometer size range. We derive a novel, theory-based, simple and robust metric for identifying the exact sizes where these effects cannot be omitted for arbitrary molecular systems. The presented metric, based on examining the second- and first-order derivatives of the particle size distribution function, is directly applicable to experimental size distribution data. This tool enables quantifying the onset of condensational growth without prior information on the properties of the vapors and particles, thus allowing robust experimental resolving of nanoparticle formation physics.

A semi-analytical solution to Brownian coagulation of fractal aggregates valid for the entire particle size range

ABSTRACTBrownian coagulation is an important particle growth mechanism in a number of aerosol processes. Analytical solution to Brownian coagulation has been an interesting subject in aerosol population dynamics field because it can provide deep insight into the nature of the coagulation process. In the case of spherical particles, analytical solutions have been derived for all different particle size regimes. For fractal aggregates that can represent the morphology of many important industrial aerosol products and combustion soot particles, however, analytical solutions have been reported only for the free-molecule and continuum regimes. In this work, a semi-analytical solution to the Brownian coagulation of fractal aggregates valid for the entire particle size range is presented using the method of moments based on the assumption of log-normal particle size distribution. The new solution is validated by limiting-case analyses as well as by comparison with a more accurate numerical solution. The characteristics of the Brownian coagulation of fractal aggregates in the transition regime are discussed using the new solution.

Characterization of the Particle Size and Polydispersity of Dicumarol Using Solid-State NMR Spectroscopy.

A variety of particle sizes of a model compound, dicumarol, were prepared and characterized in order to investigate the correlation between particle size and solid-state NMR (SSNMR) proton spin-lattice relaxation (1H T1) times. Conventional laser diffraction and scanning electron microscopy were used as particle size measurement techniques and showed crystalline dicumarol samples with sizes ranging from tens of micrometers to a few micrometers. Dicumarol samples were prepared using both bottom-up and top-down particle size control approaches, via antisolvent microprecipitation and cryogrinding. It was observed that smaller particles of dicumarol generally had shorter 1H T1 times than larger ones. Additionally, cryomilled particles had the shortest 1H T1 times encountered (8 s). SSNMR 1H T1 times of all the samples were measured and showed as-received dicumarol to have a T1 of 1500 s, whereas the 1H T1 times of the precipitated samples ranged from 20 to 80 s, with no apparent change in the physical form of dicumarol. Physical mixtures of different sized particles were also analyzed to determine the effect of sample inhomogeneity on 1H T1 values. Mixtures of cryoground and as-received dicumarol were clearly inhomogeneous as they did not fit well to a one-component relaxation model, but could be fit much better to a two-component model with both fast-and slow-relaxing regimes. Results indicate that samples of crystalline dicumarol containing two significantly different particle size populations could be deconvoluted solely based on their differences in 1H T1 times. Relative populations of each particle size regime could also be approximated using two-component fitting models. Using NMR theory on spin diffusion as a reference, and taking into account the presence of crystal defects, a model for the correlation between the particle size of dicumarol and its 1H T1 time was proposed.

Optimization of supercritical carbon dioxide extraction of Piper Betel Linn leaves oil and total phenolic content

Supercritical Carbon Dioxide (SC-CO2) Extraction was applied to extract piper betel linn leaves. The piper betel leaves oil was used antioxidant, anti-diabetic, anticancer and antistroke. The aim of this study was to optimize the conditions of pressure, temperature and flowrate for oil yield and total phenolic content. The operational conditions of SC-CO2 studied were pressure (10, 20, 30 MPa), temperature (40, 60, 80 °C) and flowrate carbon dioxide (4, 6, 8 mL/min). The constant parameters were average particle size and extraction regime, 355pm and 3.5 hours respectively. First order polynomial expression was used to express the extracted oil while second order polynomial expression was used to express the total phenolic content and the both results were satisfactory. The best conditions to maximize the total extraction oil yields and total phenolic content were 30 MPa, 80 °C and 4.42 mL/min leading to 7.32% of oil and 29.72 MPa, 67.53 °C and 7.98 mL/min leading to 845.085 mg GAE/g sample. In terms of optimum condition with high extraction yield and high total phenolic content in the extracts, the best operating conditions were 30 MPa, 78 °C and 8 mL/min with 7.05% yield and 791.709 mg gallic acid equivalent (GAE)/g sample. The most dominant condition for extraction of oil yield and phenolic content were pressure and CO2 flowrate. The results show a good fit to the proposed model and the optimal conditions obtained were within the experimental range with the value of R2 was 96.13% for percentage yield and 98.52% for total phenolic content.

Hands-on Experiments on Predatory Behaviour with Antlion Larvae

One of the innovations in the Slovenian school system has been the introduction of elective subjects in the curricula of primary and secondary schools, thus there is a lack of teaching manuals for practical exercises and hands-on classroom experience. This situation is reflected in the Ethology classroom and for that purpose we prepared step-by-step model experiments, which can be used in Ethology classes. The larvae of antlions (Myrmeleontidae) are proposed as ideal organisms for studying the effect of environmental factors on predatory behaviour. The students perform three different experiments, where the effect of substrate particle size and feeding regime on the behaviour of antlion larvae are tested. Students are made to work in three groups, and depending on the result of the first experiment, the other two experiments are performed. Students are encouraged to think about the setting, active research, thorough observation and interpretation of the data to yield meaningful information. The exercise plan is the basic principle of studying animal behaviour, and the main focus is for students to be actively involved.

Redox stratification drives enhanced growth in a deposit-feeding invertebrate: implications for aquaculture bioremediation

Effective and affordable treatment of waste solids is a key sustainability challenge for the aquaculture industry. Here, we investigated the potential for a deposit-feeding sea cucumber, Holothuria scabra, to provide a remediation service whilst concurrently yielding a high-value secondary product in a land-based recirculating aquaculture system (RAS). The effect of sediment depth, particle size and redox regime were examined in relation to changes in the behaviour, growth and biochemical composition of juvenile sea cucumbers cultured for 81 d in manipulated sediment systems, describing either fully oxic or stratified (oxic-anoxic) redox regimes. The redox regime was the principal factor affecting growth, biochemical composition and behaviour, while substrate depth and particle size did not significantly affect growth rate or biomass production. Animals cultured under fully oxic conditions exhibited negative growth and had higher lipid and carbohydrate contents, potentially due to compensatory feeding in response to higher microphytobenthic production. In contrast, animals in the stratified treatments spent more time feeding, generated faster growth and produced significantly higher biomass yields (626.89 ± 35.44 g m-2 versus 449.22 ± 14.24 g m-2; mean ± SE). Further, unlike in oxic treatments, growth in the stratified treatments did not reach maximum biomass carrying capacity, indicating that stratified sediment is more suitable for culturing sea cucumbers. However, the stratified sediments may exhibit reduced bioremediation ability relative to the oxic sediment, signifying a trade-off between remediation efficiency and exploitable biomass yield.

Asymptotic behavior of TEMOM model for particle population balance equation over the entire particle size regimes

In the present study, the asymptotic behavior of TEMOM model for particle population balance equation over the entire particle size regime has been analyzed mathematically with harmonic mean and Dahneke's solution. The results show that whether the collision kernel with Dahneke's solution or harmonic mean method in the transition regime, the relative growth rates for particle moments have the same power law as that in continuum regime at long time. The result is consistent with the physical processes in particle coagulation due to the Brownian motion. The asymptotic analysis is just based on the mathematical formulation rather than the physical assumption, and the accuracy of asymptotic solution is fully dependent on the expanded Taylor series. The results can be used to model the evolution of particle coagulation over the entire size regime at a long time, and it will reduce the computational cost greatly.

Using diamond-mined sediment discharges to test the paradigms of sandy-beach ecology

The prevailing view of sandy-shore ecosystems is that they are controlled largely by physical conditions, particularly particle size, slope and wave regime, but it is rarely possible to test this view by experimentally manipulating these attributes. We report a unique opportunity to accomplish this because large-scale alteration of these properties has taken place on the Namibian coast, associated with diamond mining. Elizabeth Bay diamond mine, near Lüderitz, started modern operations in 1991. Since then, 30.8 million tonnes of sediment with a particle size (<1.4 mm) coarser than the native beach sand have been discharged as slurry onto the beach as part of the treatment process. The physical and biological effects of this were monitored on seven occasions between 1993 and 2012, spanning three phases: (1) an initial pre-upgrade phase (1994–2004) with discharges of moderate intensity; (2) doubling of discharges during upgrade of the mine (2005–2008); (3) temporary cessation of mining (2009–2011). These vicissitudes resulted in both spatial and temporal physical changes, including massive beach accretion (350–620 m), overall increases in mean sand particle size and slope and decreases in Dean's Parameter, east-to-west gradients in beach slope, wave height and erosion, and changes in the beach state from dissipative towards reflective conditions. Alteration of physical conditions led to significant macrofaunal changes, with the community structure in the centre of the bay opposite the discharge points shifting from a state dominated by sand mussels to one dominated by peracarid crustaceans, accompanied by reductions in diversity, biomass and abundance. Grossebucht, which lies nearby and is not mined, provided comparative reference samples: physical conditions there changed little, and biotic communities were constant, significantly more diverse and had greater abundances and biomasses than at Elizabeth Bay. The changes in physical conditions and ensuing biological responses confirmed the prevailing paradigm that sandy beaches are physically driven, with diversity, abundance and biomass all declining at places and times where sediment particle size and beach slope increased due to sediment inputs.

Research on bimodal particle extinction coefficient during Brownian coagulation and condensation for the entire particle size regime

The extinction coefficient of atmospheric aerosol particles influences the earth’s radiation balance directly or indirectly, and it can be determined by the scattering and absorption characteristics of aerosol particles. The problem of estimating the change of extinction coefficient due to time evolution of bimodal particle size distribution is studied, and two improved methods for calculating the Brownian coagulation coefficient and the condensation growth rate are proposed, respectively. Through the improved method based on Otto kernel, the Brownian coagulation coefficient can be expressed simply in powers of particle volume for the entire particle size regime based on the fitted polynomials of the mean enhancement function. Meanwhile, the improved method based on Fuchs–Sutugin kernel is developed to obtain the condensation growth rate for the entire particle size regime. And then, the change of the overall extinction coefficient of bimodal distributions undergoing Brownian coagulation and condensation can be estimated comprehensively for the entire particle size regime. Simulation experiments indicate that the extinction coefficients obtained with the improved methods coincide fairly well with the true values, which provide a simple, reliable, and general method to estimate the change of extinction coefficient for the entire particle size regime during the bimodal particle dynamic processes.

Particle Habit Imaging Using Incoherent Light: A First Step toward a Novel Instrument for Cloud Microphysics

Abstract The imaging unit of the novel cloud particle instrument Particle Habit Imaging and Polar Scattering (PHIPS) probe has been developed to image individual ice particles produced inside a large cloud chamber. The PHIPS produces images of single airborne ice crystals, illuminated with white light of an ultrafast flashlamp, which are captured at a maximum frequency of ∼5 Hz by a charge-coupled device (CCD) camera with microscope optics. The imaging properties of the instrument were characterized by means of crystalline sodium hexafluorosilicate ice analogs, which are stable at room temperature. The optical resolving power of the system is ∼2 μm. By using dedicated algorithms for image processing and analysis, the ice crystal images can be analyzed automatically in terms of size and selected shape parameters. PHIPS has been operated at the cloud simulation chamber facility Aerosol Interaction and Dynamics in the Atmosphere (AIDA) of the Karlsruhe Institute of Technology at different temperatures between −17° and −4°C in order to study the influence of the ambient conditions, that is, temperature and ice saturation ratio, on ice crystal habits. The area-equivalent size distributions deduced from the PHIPS images are compared with the retrieval results from Fourier transform infrared (FTIR) extinction spectroscopy in case of small (&amp;lt;20 μm) and with single particle data from the cloud particle imager in case of larger (&amp;gt;20 μm) ice particles. Good agreement is found for both particle size regimes.

A Study of Airborne Wear Particles Generated From a Sliding Contact

Recently, much attention has been paid to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. In this study airborne particles generated from a sliding steel-on-steel combination are studied using a pin-on-disk tribometer equipped with airborne-particle counting instrumentation. The instrumentation measured particles in size intervals from 0.01μm to 32μm. The result shows three particle size regimes with distinct number peaks: ultrafine particles with a size distribution peak around 0.08μm, fine particles with a peak around 0.35μm, and coarse particles with a peak around 2 or 4μm. Both the particle generation rate and the wear rate increase with increasing sliding velocity and contact pressure.