Influence of the feeding mechanism on deposits of square particles

In a previous paper [Hidalgo et al., Phys. Rev. Lett. 103, 118001 (2009)] it was shown that square particles deposited in a silo tend to align with a diagonal parallel to the gravity, giving rise to a deposit with very particular properties. Here we explore, both experimentally and numerically, the effect on these properties of the filling mechanism. In particular, we modify the volume fraction of the initial configuration from which the grains are deposited. Starting from a very dilute case, increasing the volume fraction results in an enhancement of the disorder in the final deposit characterized by a decrease of the final packing fraction and a reduction of the number of particles oriented with their diagonal in the direction of gravity. However, for very high initial volume fractions, the final packing fraction increases again. This result implies that two deposits with the same final packing fraction can be obtained from very different initial conditions. The structural properties of such deposits are analyzed, revealing that, although the final volume fraction is the same, their micromechanical properties notably differ.

Cluster glasses of ultrasoft particles

We present molecular dynamics (MD) simulations results for dense fluids of ultrasoft, fully penetrable particles. These are a binary mixture and a polydisperse system of particles interacting via the generalized exponential model, which is known to yield cluster crystal phases for the corresponding monodisperse systems. Because of the dispersity in the particle size, the systems investigated in this work do not crystallize and form disordered cluster phases. The clusteringtransition appears as a smooth crossover to a regime in which particles are mostly located in clusters, isolated particles being infrequent. The analysis of the internal cluster structure reveals microsegregation of the big and small particles, with a strong homo-coordination in the binary mixture. Upon further lowering the temperature below the clusteringtransition, the motion of the clusters" centers-of-mass slows down dramatically, giving way to a cluster glass transition. In the cluster glass, the diffusivities remain finite and display an activated temperature dependence, indicating that relaxation in the cluster glass occurs via particle hopping in a nearly arrested matrix of clusters. Finally we discuss the influence of the microscopic dynamics on the transport properties by comparing the MD results with Monte Carlo simulations.

Particle shape and orientation in laser diffraction and static image analysis size distribution analysis of micrometer sized rectangular particles

Laser diffraction (LD) and static image analysis (SIA) of rectangular particles [United States Pharmacopeia, USP30-NF25, General Chapter <776>, Optical Miroscopy.] have been systematically studied. To rule out sample dispersion and particle orientation as the root cause of differences in size distribution profiles, we immobilize powder samples on a glass plate by means of a dry disperser. For a defined region of the glass plate, we measure the diffraction pattern as induced by the dispersed particles, and the 2D dimensions of the individual particles using LD and optical microscopy, respectively. We demonstrate a correlation between LD and SIA, with the scattering intensity of the individual particles as the dominant factor. In theory, the scattering intensity is related to the square of the projected area of both spherical and rectangular particles. In traditional LD the size distribution profile is dominated by the maximum projected area of the particles (A). The diffraction diameters of a rectangular particle with length L and breadth B as measured by the LD instrument approximately correspond to spheres of diameter ØL and ØB respectively. Differences in the scattering intensity between spherical and rectangular particles suggest that the contribution made to the overall LD volume probability distribution by each rectangular particle is proportional to A2/L and A2/B. Accordingly, for rectangular particles the scattering intensity weighted diffraction diameter (SIWDD) explains an overestimation of their shortest dimension and an underestimation of their longest dimension. This study analyzes various samples of particles whose length ranges from approximately 10 to 1000 μm. The correlation we demonstrate between LD and SIA can be used to improve validation of LD methods based on SIA data for a variety of pharmaceutical powders all with a different rectangular particle size and shape.

Oxidative potential of particles in different occupational environments: a pilot study

The oxidative potential (OP) of particulate matter has been proposed as a toxicologically relevant metric. This concept is already frequently used for hazard characterization of ambient particles but it is still seldom applied in the occupational field. The objective of this study was to assess the OP in two different types of workplaces and to investigate the relationship between the OP and the physicochemical characteristics of the collected particles. At a toll station, at the entrance of a tunnel ('Tunnel' site), and at three different mechanical yards ('Depot' sites), we assessed particle mass (PM4 and PM2.5 and size distribution), number and surface area, organic and elemental carbon, polycyclic aromatic hydrocarbon (PAH), and four quinones as well as iron and copper concentration. The OP was determined directly on filters without extraction by using the dithiothreitol assay (DTT assay-OP(DTT)). The averaged mass concentration of respirable particles (PM4) at the Tunnel site was about twice the one at the Depot sites (173±103 and 90±36 µg m(-3), respectively), whereas the OP(DTT) was practically identical for all the sites (10.6±7.2 pmol DTT min(-1) μg(-1) at the Tunnel site; 10.4±4.6 pmol DTT min(-1) μg(-1) at the Depot sites). The OP(DTT) of PM4 was mostly present on the smallest PM2.5 fraction (OP(DTT) PM2.5: 10.2±8.1 pmol DTT min(-1) μg(-1); OP(DTT) PM4: 10.5±5.8 pmol DTT min(-1) μg(-1) for all sites), suggesting the presence of redox inactive components in the PM2.5-4 fraction. Although the reactivity was similar at the Tunnel and Depot sites irrespective of the metric chosen (OP(DTT) µg(-1) or OP(DTT) m(-3)), the chemicals associated with OP(DTT) were different between the two types of workplaces. The organic carbon, quinones, and/or metal content (Fe, Cu) were strongly associated with the DTT reactivity at the Tunnel site whereas only Fe and PAH were associated (positively and negatively, respectively) with this reactivity at the Depot sites. These results demonstrate the feasibility of measuring of the OP(DTT) in occupational environments and suggest that the particulate OP(DTT) is integrative of different physicochemical properties. This parameter could be a potentially useful exposure proxy for investigating particle exposure-related oxidative stress and its consequences. Further research is needed mostly to demonstrate the association of OP(DTT) with relevant oxidative endpoints in humans exposed to particles.

Drug loading of mesoporous silicon particles

Porous silicon (PSi) is a promising material to be utilized in drug delivery formulations. The release rate of the drug compound can be controlled by changing the pore properties and surface chemistry of PSi. The loading of a poorly soluble drug into mesoporous silicon particles enhances its dissolution in the body. The drug loading is based on adsorption. The attainable maximum loaded amount depends on the properties of the drug compound and the PSi material, and on the process conditions. The loading solvent also essentially affects the adsorption process. The loading of indomethacin into PSi particles with varying surface modification was studied. Solvent mixtures were applied in the loading, and the loaded samples were analyzed with thermal analysis methods. The best degree of loading was obtained using a mixture of dichloromethane and methanol. The drug loads varied from 7.7 w-% to 26.8 w-%. A disturbing factor in the loading experiments was the tendency of indomethacin to form solvates with the solvents applied. In addition, the physical form and stability of indomethacin loaded in PSi and silica particles were studied using Raman spectroscopy. In the case of silica, the presence of crystalline drug as well as the polymorph form can be detected, but the method proved to be not applicable for PSi particles.

Characterisation of pigment particles by scanning electron microscope and image analysis programs

Coating and filler pigments have strong influence to the properties of the paper. Filler content can be even over 30 % and pigment content in coating is about 85-95 weight percent. The physical and chemical properties of the pigments are different and the knowledge of these properties is important for optimising of optical and printing properties of the paper. The size and shape of pigment particles can be measured by different analysers which can be based on sedimentation, laser diffraction, changes in electric field etc. In this master's thesis was researched particle properties especially by scanning electron microscope (SEM) and image analysis programs. Research included nine pigments with different particle size and shape. Pigments were analysed by two image analysis programs (INCA Feature and Poikki), Coulter LS230 (laser diffraction) and SediGraph 5100 (sedimentation). The results were compared to perceive the effect of particle shape to the performance of the analysers. Only image analysis programs gave parameters of the particle shape. One part of research was also the sample preparation for SEM. Individual particles should be separated and distinct in ideal sample. Analysing methods gave different results but results from image analysis programs corresponded even to sedimentation or to laser diffraction depending on the particle shape. Detailed analysis of the particle shape required high magnification in SEM, but measured parameters described very well the shape of the particles. Large particles (ecd~1 µm) could be used also in 3D-modelling which enabled the measurement of the thickness of the particles. Scanning electron microscope and image analysis programs were effective and multifunctional tools for particle analyses. Development and experience will devise the usability of analysing method in routine use.

Nanoparticle Labels in Bioaffinity Assays

Nanoparticles offer adjustable and expandable reactive surface area compared to the more traditional solid phase forms utilized in bioaffinity assays due to the high surface to-volume ratio. The versatility of nanoparticles is further improved by the ability to incorporate various molecular complexes such as luminophores into the core. Nanoparticle labels composed of polystyrene, silica, inorganic crystals doped with high number of luminophores, preferably lanthanide(III) complexes, are employed in bioaffinity assays. Other label species such as semiconductor crystals (quantum dots) or colloidal gold clusters are also utilized. The surface derivatization of such particles with biomolecules is crucial for the applicability to bioaffinity assays. The effectiveness of a coating is reliant on the biomolecule and particle surface characteristics and the selected coupling technique. The most critical aspects of the particle labels in bioaffinity assays are their size-dependent features. For polystyrene, silica and inorganic phosphor particles, these include the kinetics, specific activity and colloidal stability. For quantum dots and gold colloids, the spectral properties are also dependent on particle size. This study reports the utilization of europium(III)-chelate-embedded nanoparticle labels in the development of bioaffinity assays. The experimental covers both the heterogeneous and homogeneous assay formats elucidating the wide applicability of the nanoparticles. It was revealed that the employment of europium(III) nanoparticles in heterogeneous assays for viral antigens, adenovirus hexon and hepatitis B surface antigen (HBsAg), resulted in sensitivity improvement of 10-1000 fold compared to the reference methods. This improvement was attributed to the extreme specific activity and enhanced monovalent affinity of the nanoparticles conjugates. The applicability of europium(III)-chelate-doped nanoparticles to homogeneous assay formats were proved in two completely different experimental settings; assays based on immunological recognition or proteolytic activity. It was shown that in addition to small molecule acceptors, particulate acceptors may also be employed due to the high specific activity of the particles promoting proximity-induced reabsorptive energy transfer in addition to non-radiative energy transfer. The principle of proteolytic activity assay relied on a novel dual-step FRET concept, wherein the streptavidin-derivatized europium(III)-chelate-doped nanoparticles were used as donors for peptide substrates modified with biotin and terminal europium emission compliant primary acceptor and a secondary quencher acceptor. The recorded sensitized emission was proportional to the enzyme activity, and the assay response to various inhibitor doses was in agreement with those found in literature showing the feasibility of the technique. Experiments regarding the impact of donor particle size on the extent of direct donor fluorescence and reabsorptive excitation interference in a FRET-based application was conducted with differently sized europium(III)-chelate-doped nanoparticles. It was shown that the size effect was minimal

Morphological study of Sr2CeO4 blue phosphor with fine particles

Morphological and spectroscopic studies of Sr2CeO4 blue phosphor in the form of fine particles prepared from a powdered multi-component precursor, via a combustion method, are reported. Samples were also prepared through a solid-state reaction and from a polymeric precursor for comparison. Citric acid or glycine as fuels in the combustion method lead to a mixture which is heated at 950 ºC for 4 h, resulting in spheroidal particles with a diameter between 250-550 nm. Samples from the polymeric precursor result in spheroidal particles (350-550 nm) and from the solid-state reaction in irregular particles (~ 5 mum). Therefore, the combustion method is adequate for preparation of Sr2CeO4 in the form of spherical fine particles.

Formation of TiO2 photoanodes by simultaneous electrophoretic deposition of anatase and rutile particles for photoassisted electrolytic copper ions removal

The influence of Anatasa/Rutile ratio on TiO2 films, grown by electrophoretic deposition was studied in the photoassisted electrolytic copper ions removal from cyanide solutions. The proper dispersant dosage allowing the simultaneous electrophoretic deposition of Anatase and Rutile was chosen based on electrokinetic measurements; evidenced by the XRD spectra of the formed films. The evaluation of films photoassisted electrolytic copper ion removal showeds that it is possible to enhance the activity of Anatase films by adding some Rutile exploiting the synergetic interaction between these two materials, achieve by its proper deposition.

Preparation and evaluation of magnetic chitosan particles modified with ethylenediamine and Fe(III) for the removal of Cr(VI) from aqueous solutions

The adsorption of Cr(VI) in aqueous solution by magnetic particles of crosslinked chitosan-ethylenediamine-Fe(III) (MPCh-EDA-FeCL) was studied in a batch system. Fe3+ in the MPCh-EDA-FeCL permitted that adsorption of Cr(VI) occurred with maximum efficiency between pH 3 and 11. The maximum adsorption capacity at pH 7.0 was 81.04 mg g-1 at 25 ºC. The adsorption kinetic process was described by the pseudo-second-order model. Thermodynamic parameters indicated spontaneous, exothermic and chemical adsorption nature. The adsorbent was successively regenerated using a 0.1 mol L-1 NaOH solution. Results were satisfactory for treatment of wastewater from the electroplating industry.

Ni(II), Cu(II), AND Zn(II) COMPLEXES DERIVED FROM A NEW SCHIFF BASE 2-((Z)-(3-METHYLPYRIDIN-2- YLEIMINO)METHYL)PHENOL AND SYNTHESIS OF NANO SIZED METAL OXIDE PARTICLES FROM THESE COMPOUNDS

Synthesis, spectral identification, and magnetic properties of three complexes of Ni(II), Cu(II), and Zn(II) are described. All three compounds have the general formula [M(L)2(H2O)2], where L = deprotonated phenol in the Schiff base 2-((z)-(3-methylpyridin-2-yleimino)methyl)phenol. The three complexes were synthesized in a one-step synthesis and characterized by elemental analysis, Fourier transform infrared spectroscopy, electronic spectra, X-ray diffraction (XRD), and room temperature magnetic moments. The Cu(II) and Ni(II) complexes exhibited room temperature magnetic moments of 1.85 B.M. per copper atom and 2.96 B.M. per nickel atom. The X-band electron spin resonance spectra of a Cu(II) sample in dimethylformamide frozen at 77 K (liquid nitrogen temperature) showed a typical ΔMS = ± 1 transition. The complexes ([M(L)2(H2O)2]) were investigated by the cyclic voltammetry technique, which provided information regarding the electrochemical mechanism of redox behavior of the compounds. Thermal decomposition of the complexes at 750 ºC resulted in the formation of metal oxide nanoparticles. XRD analyses indicated that the nanoparticles had a high degree of crystallinity. The average sizes of the nanoparticles were found to be approximately 54.3, 30.1, and 44.4 nm for NiO, CuO, and ZnO, respectively.

Imaging and Characterisation of Dirt Particles in Pulp and Paper

Dirt counting and dirt particle characterisation of pulp samples is an important part of quality control in pulp and paper production. The need for an automatic image analysis system to consider dirt particle characterisation in various pulp samples is also very critical. However, existent image analysis systems utilise a single threshold to segment the dirt particles in different pulp samples. This limits their precision. Based on evidence, designing an automatic image analysis system that could overcome this deficiency is very useful. In this study, the developed Niblack thresholding method is proposed. The method defines the threshold based on the number of segmented particles. In addition, the Kittler thresholding is utilised. Both of these thresholding methods can determine the dirt count of the different pulp samples accurately as compared to visual inspection and the Digital Optical Measuring and Analysis System (DOMAS). In addition, the minimum resolution needed for acquiring a scanner image is defined. By considering the variation in dirt particle features, the curl shows acceptable difference to discriminate the bark and the fibre bundles in different pulp samples. Three classifiers, called k-Nearest Neighbour, Linear Discriminant Analysis and Multi-layer Perceptron are utilised to categorize the dirt particles. Linear Discriminant Analysis and Multi-layer Perceptron are the most accurate in classifying the segmented dirt particles by the Kittler thresholding with morphological processing. The result shows that the dirt particles are successfully categorized for bark and for fibre bundles.

Substrate with Organosuper® for cucumber seedlings formation in protected environments and polystyrene trays

Culture environments, trays and doses of organic compost were evaluated in the formation of cucumber seedlings (Cucumis sativus L.). Five environmental conditions were tested: (A1) a greenhouse with height of 2.5 m, covered with polyethylene film, (A2) nursery with height of 2.5 m, monofilament fabric, 50% shading, (A3) nursery with height of 2.5 m, heat-reflective screen, 50% shading, (A4) nursery with a height of 1.8 m, covered with coconut tree straw and (A5) greenhouse with height of 4.0 m, covered with polyethylene film, with zenith opening and thermo-reflective cloth under the plastic. Trays of 72 (R1) and 128 (R2) cells were filled with 93% soil and 7% organic compound (S1), 86% soil and 14% organic compound (S2) and 79% soil and 21% organic compound (S3). It was used a randomized design in split-split-plot scheme, with five replicates (environments x trays x substrates). The greenhouses provide the best environments for the formation of cucumber seedlings. A tray of 72 cells is the best container, promoting more vigorous seedlings in substrate with soil and 7 or 14% organic compound.

Specific surface charging of latex, clay and mineral oxide particles in aqueous, non-aqueous and mixed solvent systems

En djupare förståelse för växelverkan mellan partiklar i suspensioner är av betydelse för utvecklingen av en mängd olika industriella produkter och processer. Till exempel kan nämnas pigmentbaserade färger och bestrykning av papper. Genom att öka kontrollbarheten kan dessa lättare optimeras för att uppnå förbättrade produktegenskaper och/eller sänkta produktionskostnader. Av stor betydelse är även en förbättrad möjlighet att minska produktens miljöpåverkan. I avhandlingen studerades jonstyrkan och jonspecificiteten inverkan i olika akvatiska suspensioner innehållande olika elektrolyter. De partiklar som avhandlingen omfattade var metalloxider, leror samt latex. Jonstyrkan studerades från låga (c <10-3M) till och med höga (c> 10-1M) elektrolytkoncentrationer. Vid koncentrationer under 0.1 M var partikelladdningen styrd av pH och jonstyrkan. Vid högre elektrolytkoncentrationer påverkade även jonspecificiteten partikelladdningen. Jonspecificiteten arrangerades i fenomenologiska serier funna i litteraturen samt med Born modellen definierad i termodynamiken. Överraskande höga absoluta zeta-potential värden erhölls vid höga elektrolytkoncentrationer vilket visar att den elektrostatiska repulsionen har betydelse även vid dessa förhållanden. Vidare studerades titanoxidsuspensioners egenskaper i akvatiska, icke-akvatiska och blandade lösningssystem under varierande koncentration av oxal- och fosfatsyra. Vid lågt vatteninnehåll studerades även suspensioner med svavelsyra. Konduktiviteten i suspensioner med lågt vatteninnehåll ökade med tillsatt oxal- eller fosforsyra vilket är en omvänd effekt jämfört med svavelsyra eller akvatiska suspensioner. Den omvända effekten skiftade gradvis tillbaka med ökad vatteninnehåll. En analys av suspensionernas adsorption i höga etanolkoncentrationer gjordes med konduktiviteten, pH och zeta-potentialen. Viskositet studerades och applicerades framgångsrikt i viskositet/ytladdningsmodeller utvecklade för akvatiska suspensioner.