Spheres Of Different Sizes Research Articles

Encapsulation of spherical nanoparticles by colloidal dimers.

We study by Monte Carlo simulation the coating process of colloidal dimers onto spherical nanoparticles. To this end we investigate a simplified mixture of hard spheres (the guest particles) and hard dimers formed by two tangent spheres of different sizes (the encapsulating agents) in an implicit-solvent representation; in our scheme, the range of effective interactions between the smaller particle in a dimer and a guest sphere depends on their relative size. By tuning the size and concentration of guests, under overall dilute conditions a rich phase behavior emerges: for small sizes and/or low concentrations, the preferred arrangement is compact aggregates (capsules) of variable sizes, where one or few guest particles are coated with dimers; for larger sizes and moderate guest concentrations, other scenarios are realized, including equilibrium separation between a guest-rich and a guest-poor phase. Our results serve as a framework for a more systematic investigation of self-assembled structures of functionalized dimers capable of encapsulating target particles, like for instance bioactive substances in a colloidal dispersion.

Investigation of selective etching mechanism and its dependency on the particle size in preparation of hollow silica spheres

In this paper, the core–shell SiO2@mSiO2/CTAB spheres were fabricated by choosing the solid silica spheres of different sizes as the internal cores, then a series of etching experiments were conducted. For different etching time and particle size, different rattle-type or hollow silica spheres were obtained. Investigation showed that CTAB in the mesoporous shell played a very important role to the selectivity of the etching. Both the rattle-type and hollow structures were successfully fabricated by adjusting the etching time in the presence of CTAB but without obvious etching of mesoporous silica shell. More importantly, the morphology transformation depended on the particle size of the solid silica cores. Generally, when the particle size of the internal cores was very small (d 1 μm), the rattle-type microspheres with at least double-shell structure were first obtained after a certain period of etching time, then the hollow spheres with multi-shell structure were obtained with prolonging etching time. It is further revealed that both the rattle-type and hollow silica spheres with multi-shell structure could be prepared successfully if the particle size of the solid silica core was large enough.

Mechanical Bowel Preparation Versus no Preparation in Elective Colorectal Surgery: A Prospective Randomised Study

Resummed thermodynamic perturbation theory for central force associating potential is extended and applied to study the properties of shielded attractive shell model of polymerizing hard spheres of different sizes. The model is represented by the two-component mixture of hard spheres with additional square-well interaction treated in the sticky limit and located inside the hard-core region and acting only between particles of different species. The theory self-consistently takes into account the changes in the excluded volume of the system due to bonding of the particles. Theoretical predictions for the pressure and fraction of the particles in different bonding states at different temperatures and densities are compared against computer simulation predictions. The theory appears to be very accurate in description of the dimerizing and trimerizing versions of the model. For the model, which allows chain polymerization the theory is slightly less accurate, in particular for low temperatures and high densities.

Electromagnetic resonant modes of dielectric sphere bilayers

Sphere bilayers have been proposed as promising structures for electromagnetic management in photonic crystal devices. These arrangements are made of two intertwined subsets of spheres of different size and refractive index, one subset filling the interstitial sites of the other. We present a systematic study of the electromagnetic resonant modes of the bilayers, in comparison with those of the constituent subsets of spheres. Three samples were built with glass and Teflon spheres and their transmission spectra measured in the microwave range (10–25 GHz). Simulations with finite integration time-domain method are in good agreement with experiments. Results show that the bilayer presents the same resonances as one of the subsets but modified by the presence of the other in its resonant frequencies and in the electric field distributions. As this distortion is not very large, the number of resonances in a selected spectral region is determined by the dominant subset. The degree of freedom that offers the bilayer could be useful to fine tune the resonances of the structure for different applications. A map of modes useful to guide this design is also presented. Scale invariance of Maxwell equations allows the translation of these results in the microwave range to the visible region; hence, some possible applications are discussed in this framework.

Particle Shape Effects on Subvisible Particle Sizing Measurements

Particle analysis tools for the subvisible (<100 μm) size range, such as light obscuration, flow imaging (FI), and electrical sensing zone (ESZ), often produce results that do not agree with one another, despite their general agreement when characterizing polystyrene latex spheres of different sizes. To include the effect of shape in comparison studies, we have used the methods of photolithography to create rods and disks. Although the rods are highly monodisperse, the instruments produce broadened peaks and report mean size parameters that are different for different instruments. We have fabricated a microfluidic device that simultaneously performs ESZ and FI measurements on each particle to elucidate the causes of discrepancies and broadening. Alignment of the rods with flow causes an oversizing by FI and undersizing by ESZ. FI also oversizes rods because of the incorrect edge definition that results from diffraction and imperfect focus. We present an improved correction algorithm for this effect that reduces discrepancies for rod-shaped particles. Tumbling of particles is observed in the microfluidic ESZ/FI and results in particle oversizing and breadth of size distribution for the monodisperse rods.

Microwave Synthesized Monodisperse CdS Spheres of Different Size and Color for Solar Cell Applications

Monodisperse CdS spheres of size of 40 to 140 nm were obtained by microwave heating from basic solutions. It is observed that larger CdS spheres were formed at lower solution pH (8.4–8.8) and smaller ones at higher solution pH (10.8–11.3). The color of CdS products changed with solution pH and reaction temperature; those synthesized at lower pH and temperature were of green‐yellow color, whereas those formed at higher pH and temperature were of orange‐yellow color. A good photovoltage was observed in CdS:poly(3‐hexylthiophene) solar cells with spherical CdS particles. This is due to the good dispersion of CdS nanoparticles in P3HT solution that led to a large interface area between the organic and inorganic semiconductors. Higher photocurrent density was obtained in green‐yellow CdS particles of lower defect density. The efficient microwave chemistry accelerated the hydrolysis of thiourea in pH lower than 9 and produced monodisperse spherical CdS nanoparticles suitable for solar cell applications.

Comparison of experimental and simulated effective thermal conductivity of polymer matrix filled with metallic spheres: Thermal contact resistance and particle size effect

In this paper, we present a numerical and experimental study of a composite material with conducting spheres embedded in a polymer matrix. Our main objective is to study how the particle size and thermal contact affect the overall thermal properties of composites. In the numerical study, finite elements method is used to model heat transfer and to calculate the effective thermal conductivity. A periodical method was used to measure simultaneously thermal conductivity and diffusivity of the composite consisting of an epoxy resin matrix filled with brass spheres of different sizes. A comparison between the numerically calculated, measured and analytical thermal conductivity values for various samples is performed and the significance of the findings is discussed in the paper.

Structure of spherical electric double layers with fully asymmetric electrolytes: a systematic study by Monte Carlo simulations and density functional theory.

A systematic investigation of the spherical electric double layers with the electrolytes having size as well as charge asymmetry is carried out using density functional theory and Monte Carlo simulations. The system is considered within the primitive model, where the macroion is a structureless hard spherical colloid, the small ions as charged hard spheres of different size, and the solvent is represented as a dielectric continuum. The present theory approximates the hard sphere part of the one particle correlation function using a weighted density approach whereas a perturbation expansion around the uniform fluid is applied to evaluate the ionic contribution. The theory is in quantitative agreement with Monte Carlo simulation for the density and the mean electrostatic potential profiles over a wide range of electrolyte concentrations, surface charge densities, valence of small ions, and macroion sizes. The theory provides distinctive evidence of charge and size correlations within the electrode-electrolyte interface in spherical geometry.

Ceramic Photonic Glass for Broadband Omnidirectional Reflection

We report on the fabrication and properties of ceramic photonic glass, a disordered arrangement of monodisperse ceramic spheres with diameters in the range of the wavelengths of incident light. These novel materials are produced as solid thin films which can be used for a wide range of applications, such as broadband visible reflectors, thermal radiation barrier coatings, high temperature stable structural coloration, resonant random lasers and media for photonic Anderson localization. Large nearly monodisperse spheres of different sizes were obtained by methods of sol–gel chemistry. Photonic glass films with layer thickness varied in the range 7–100 μm were deposited by drop casting from suspensions in ethylene glycol. Larger particles demonstrate a larger spectral window of broadband reflection. For thermal barrier coating applications strong reflection in the wavelength range of 1–6 μm is obtained with particles close to 3 μm diameter.

Target volume segmentation of PET images by an iterative method based on threshold value

ObjectivesAn automatic segmentation method is presented for PET images based on an iterative approximation by threshold value that includes the influence of both lesion size and background present during the acquisition. Material and methodsOptimal threshold values that represent a correct segmentation of volumes were determined based on a PET phantom study that contained different sizes of spheres and different known radiation environments. These optimal values were normalized to background and adjusted by regression techniques to a two-variable function: lesion volume and signal-to-background ratio (SBR). This adjustment function was used to build an iterative segmentation method. Based on this method, a procedure of automatic delineation was proposed. This procedure was validated on phantom images and its viability was confirmed by retrospectively applying it on two oncology patients. ResultsThe resulting adjustment function obtained had a linear dependence with the SBR and was inversely proportional and negative with the volume. During the validation of the proposed method, it was found that the volume deviations with respect to its real value and CT volume were below 10% and 9%, respectively, except for lesions with a volume below 0.6ml. ConclusionsThe automatic segmentation method proposed can be applied in clinical practice to tumor radiotherapy treatment planning in a simple and reliable way with a precision close to the resolution of PET images.

Влияние криоконсервирования путем медленного замораживания или витрификации на жизнеспособность и метаболическую активность мезенхимальных стромальных клеток, заключенных в альгинатные сферы с диаметром более 1 мм

The aim of the study was to evaluate the effect of exposure duration of alginate encapsulated mesenchymal stromal cells (MSCs) in multicomponent cryoprotective solution DEPS-1 (10% dimethyl sulfoxide, 20% ethylene glycol, 1,2-propane diol and0.5 M sucrose) on survival and metabolic activity following cryopreservation using vitrification. The spheres of 1mm diameter obtained by dropwise addition of sodium alginate into calcium chloride were used in the experiments. Alginate spheres derived by this method contained more cells as compared to the spheres of (0.5 ± 0.2) mm derived by pulverizing the alginate into calcium chloride. It was shown that using of multicomponent cryoprotective solution DEPS-1 allowed achieving successful cryopreservation of MSCs encapsulated in alginate spheres of different sizes. It was found that saturation with cryoprotective solution of MSCs encapsulated in spheres with 1.2 mm size needed a longer exposure with CPA if compared with spheres of 0.6 mm size. Probl Cryobiol Cryomed 2014; 24(3):222-230.

Inverse Opal Carbons As Li-O2 Cathodes with an Ionic Liquid-Based Electrolyte: Effect of Macropore Size on Capacity, Rate Capability and Reversibility

Inverse opals are beautiful macroporous materials prepared by template synthesis and presenting a well-defined arrangement of pores of tunable monodisperse size. Thus, they are ideal model systems for studying the effect of macropore size in lithium-oxygen electrodes.In this work, inverse opal carbons were prepared by using poly(styrene-co-methacrylic acid) (PS-MAA) spheres of different size as templates via a resorcinol-formaldehyde sol-gel process. These were used in cathodes for Li-O2 batteries using different cell configurations and an ionic liquid electrolyte (LiTFSI in PYR14TFSI). The high porosity and open channels with low tortuosity allowed remarkable capacities of over 3000 mAh/g at 0.1 mA/cm2.We could relate the carbon textural properties to the capacity, rate capability and reversibility. We observed better rate capability for discharge with the largest macropores (500 nm diameter), evidencing a mass transport limitation. However, charge profiles denoted a remarkable asymmetry respect to discharge, with low coulomb efficiency. Instead, when macropores were smaller than 100 nm we obtained a remarkable symmetry in time-limited discharge-charge profiles. This proves that confinement of discharge products in small pores effectively prevents the electrode passivation. Acknowledgement The research leading to these results has received funding from the European Union’s Seventh Framework Programme under EC-GA No. 265971 ‘LABOHR’, and from the Spanish Government under contract MAT2012-39199-C02-01. M.O. acknowledges CSIC for a JAE-DOC research contract.

Les complications des microgreffes de cheveux

Resummed thermodynamic perturbation theory for central force associating potential is extended and applied to study the properties of shielded attractive shell model of polymerizing hard spheres of different sizes. The model is represented by the two-component mixture of hard spheres with additional square-well interaction treated in the sticky limit and located inside the hard-core region and acting only between particles of different species. The theory self-consistently takes into account the changes in the excluded volume of the system due to bonding of the particles. Theoretical predictions for the pressure and fraction of the particles in different bonding states at different temperatures and densities are compared against computer simulation predictions. The theory appears to be very accurate in description of the dimerizing and trimerizing versions of the model. For the model, which allows chain polymerization the theory is slightly less accurate, in particular for low temperatures and high densities.

Multiple scattering in dispersions, for long wavelength thermoacoustic solutions

Thermoacoustic scattering is a principal scattering mechanism in the ultrasonic characterisation of water-continuous colloids. Thermal effects are particularly important in highly concentrated systems, where non-propagational thermal fields surrounding the disperse particles overlap. For low concentrations, the single sphere solution of Epstein and Carhart has become a popular tool for determining the particle size distribution. However, for small particle sizes it suffers from ill-conditioning that can make the solution numerically unstable. This problem has been resolved, by Harlen et. al. (2001, SIAM Journal on Applied Mathematics, 61 1906-1931), who obtained an asymptotic solution for low concentrations that is valid when the particle diameter is small compared to the wavelength. In this paper we will use this asymptotic method to calculate the effects of multiple scattering that occur at higher concentrations. We use the addition translation theorem to calculate the effects of multiple scattering between a pair of spheres of different sizes and show how this affects the close-field scattering pattern.

Flaming Ignition Behavior of Hot Steel and Aluminum Spheres Landing in Cellulose Fuel Beds

The ignition of combustible material by hot metal particles is an important fire ignition pathway that remains relatively unstudied. In this work, the flaming ignition behavior of powdered cellulose fuel beds by hot steel and aluminum spheres of various diameters and initial temperatures was studied. Understanding ignition in this scenario could offer insight into the mechanisms by which metal particles initiate wildland fires and fires in industrial settings. Earlier work on this topic has shown that ignition propensity has a relationship with the temperature and diameter of the sphere. However, little is known about the physical processes governing this relationship. This work provides further information regarding the conditions required for ignition, and useful observations for the development of a theoretical framework for predicting ignition propensity of combustible fuel beds. For the conditions tested, powdered cellulose ignition appears to exhibit limiting behavior in two regimes: for larger spheres, temperatures below 600 C did not ignite the cellulose and spheres with diameters below 2.38 mm for steel or 2.03 mm for aluminum and temperatures up to 1100 C did not ignite the cellulose either. We also observed that in the range of sphere diameters from 4-8 mm, aluminum spheres of a given diameter are more likely to cause ignition than their steel counterparts. This seems to be due to the fact that the aluminum spheres are molten at temperatures greater than 657.2 C; melting contributes to a spheres bulk energy through the latent heat of melting and allows for sphere deformation and splatter during impact. Furthermore, qualitative analysis of high speed schlieren videos shows differences in pyrolysis and ignition behavior and suggests that, different controlling processes may be at work for spheres of different sizes and for molten versus solid spheres.

Cluster Size Effects in the Surface-Enhanced Raman Scattering Response of Ag and Au Nanoparticle Aggregates: Experimental and Theoretical Insight

In this work we report the spectral evolution of the surface-enhanced Raman scattering (SERS) response of biotin molecules that generate the assembly of Ag and Au nanospheres (NSs) into clusters with controlled interparticle gaps during the aggregation process. The experiments are analyzed using rigorous near-field electrodynamic calculations of the enhancement produced in a close-packed cluster with a different number of NSs. Two kinetic mechanisms during the NS aggregation were identified which give rise to a different cluster size distribution and as a consequence to a different SERS response. It is found that during NS aggregation there is an initial fast growth of the SERS signals followed by a decay that reaches an almost constant value at relatively long times. These results are qualitatively explained by the trends observed in the electrodynamics calculations of the near-field enhancement as a function of the cluster size, which highlights the critical role played by radiation damping as the size of the cluster increases for small clusters (dimers and trimers), in contrast with the behavior observed for clusters with a relative greater number of particles where the decrease of the near-field enhancement is less significant. In addition, a general procedure is presented that makes it possible to perform a suitable comparison of the SERS response for tight-compact clusters, in the limit of large clusters, as long as the wavelength range of the SERS response is almost size independent. This procedure is tested for Ag and Au nanoaggregates generated in solution formed by spheres of different size, at an almost constant interparticle separation. It was found that even there are differences between the analytic enhancement factor and the calculated enhancement predicted by the electrodynamic theory in the large cluster size limit, and the trends in the SERS response of the biotin molecules are qualitatively explained by the electromagnetic (EM) mechanism for both Ag and Au clusters. These discrepancies could be indicative of a chemical contribution to the global SERS response, but a rigorous assessment of this mechanism would require additional theoretical calculations supported by experiments. Notwithstanding, the SERS enhancement results obtained with noncovalent bonded dye molecules (Coumarin 440 and Rhodamine B) that are randomly distributed in the clusters as Raman reporters, using the same large clusters as substrates (linked by biotin molecules), are in fairly good quantitative agreement with the electrodynamics model of the average SERS enhancement.

Stokes flow past three spheres

In this paper we present a numerical method to calculate the dynamics of three spheres in a quiescent viscous fluid. The method is based on Lamb’s solution to Stokes flow and the Method of Reflections, and is arbitrarily accurate given sufficient computer memory and time. It is more accurate than multipole methods, but much less efficient. Although it is too numerically intensive to be suitable for more than three spheres, it can easily handle spheres of different sizes. We find no convergence difficulties provided we study mobility problems, rather than resistance problems.After validating against the existing literature, we make a direct comparison with Stokesian Dynamics (SD), and find that the largest errors in SD occur at a sphere separation around 0.1 radius. Finally, we present results for an example system having different-sized spheres.

Effects of architecture on the electrochemistry of binder-free inverse opal carbons as Li–air cathodes in an ionic liquid-based electrolyte

In this work, different electrodes consisting of a layer of nanostructured binderless carbon supported on a stainless steel (SS) mesh have been developed and tested as cathodes for Li–air batteries. Inverse opal (IO) carbons were developed using poly(styrene-co-methacrylic acid) (PS-MAA) spheres of different sizes as templates via a resorcinol–formaldehyde sol–gel process. The resulting electrodes, which were mechanically stable and easy to manipulate, were electrochemically tested at both 25 and 60 °C by galvanostatic cycling in an ionic liquid-based electrolyte (0.3 M LiTFSI in PYR14TFSI). Different ratios of co-monomers used in the preparation of the template polymeric spheres to control their size significantly influenced the resulting surface area, pore volume and pore distribution in IO carbons of different macropore size. From the electrochemical characterisation, transverse trends in reversibility and rate capability were identified depending on the macropore size of the inverse opal carbon. Smaller pores favor a better charge–discharge reversibility. Large pores contribute to an improved rate capability and large capacity, which are likely due, respectively, to deeper oxygen diffusion into the electrode, and to larger pore bottlenecks.

Understanding and tuning the self-assembly of polyether-based triblock terpolymers in aqueous solution

The synthesis and self-assembly of well-defined poly(ethylene oxide)-block-poly(allyl glycidyl ether)-block-poly(tert-butyl glycidyl ether) (PEO-b-PAGE-b-PtBGE) triblock terpolymers with varying block lengths of PAGE and PtBGE are reported. The materials were synthesized using sequential living anionic ring-opening polymerization (AROP). The middle block, PAGE, was further modified by post-polymerization addition of 2,3,4,6-tetra-O-acetyl-1-thio-β-D-galactopyranose via thiol–ene chemistry, resulting in PEO-b-PAGEGal-b-PtBGE. Self-assembly of the terpolymers in aqueous media resulted in the predominant formation of core–shell–corona architectures and the aggregates featured a PtBGE core, a PAGE shell, and a PEO corona. The structures were investigated using dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM) measurements. In addition, the presence of a PEO corona rendered the formed micellar structures thermo-responsive, as demonstrated using turbidimetry. Depending on the ratio of hydrophilic to hydrophobic segments and on the thermal history of the samples, several micellar morphologies could be identified, including spheres of different size, worm-like structures, and vesicles. More important, both reversible and irreversible structural rearrangements could be identified during the heating–cooling cycles.

Ductile Ti-based metallic glass spheres

Here the authors have investigated the mechanical responses of Ti 40 Zr 25 Ni 3 Cu 12 Be 20 metallic glassy spheres. Smaller spheres exhibit a near homogeneous deformation behavior, whereas larger spheres display a quasi-brittle feature upon compressive loading. Meanwhile, the nanohardness value decreases with decreasing sample size. The variation in mechanical performance of the glassy spheres of different sizes is interpreted within the framework of free volume theory.