Ultralow elastic stability of salt ice at low temperatures

A model is developed to describe the elastic stability of saline ice with a homogeneous distribution of the components in the volume at high pressures (P > 0.1 GPa) and low temperatures (T < 220 K). This model is based on the basic principles of the theory of elastic percolation and the theory of ion hydration (formation of spherical clusters with water molecule dipoles oriented toward ions) in a liquid solution. This model can be used to find the dependence of the elastic stability of an ice solution on the concentration and temperature for any salts decomposing into ions with various valences and effective radii. Good agreement between the calculated and experimental dependences indicates the existence of hydration spheres in an ice solution, which is characterized by a narrower size distribution of spheres as compared to the liquid state and by a steeper decrease in the sphere size when the salt concentration increases in the range x ?? 0.001?C0.01. The stability of a solid ice solution depends on the temperature and the salt concentration in a complicated manner, having specific features in the form of maxima near phase transitions in a water matrix as a result of competing effects that enhance or weaken the elastic contributions of the frozen spheres. As follows from the model calculations, solid ice solutions can have an ultralow elastic stability (which is lower than that of pure water ice by a factor of 5?C30), which was experimentally detected even at low weight fractions of salts at a level of x ?? 0.0001?C0.01 for T < 220 K.     

Temperature and magnetic field responsive hyaluronic acid particles with tunable physical and chemical properties

We report the preparation and characterization of thiolated-temperature-responsive hyaluronic acid-cysteamine-N-isopropyl acrylamide (HA-CYs-NIPAm) particles and thiolated-magnetic-responsive hyaluronic acid (HA-Fe-CYs) particles. Linear hyaluronic acid (HA) crosslinked with divinyl sulfone as HA particles was prepared using a water-in-oil micro emulsion system which were then oxidized HA-O with NaIO₄ to develop aldehyde groups on the particle surface_. HA-O hydrogel particles were then reacted with cysteamine (CYs) which interacted with aldehydes on the HA surface to form HA particles with cysteamine (HA-CYs) functionality on the surface. HA-CYs particles were further exposed to radical polymerization with NIPAm to obtain temperature responsive HA-CYs-NIPAm hydrogel particles. To acquire magnetic field responsive HA composites, magnetic iron particles were included in HA to form HA-Fe during HA particle preparation. HA-Fe hydrogel particles were also chemically modified. The prepared HA-CYs-NIPAm demonstrated temperature dependent size variations and phase transition temperature. HA-CYs-NIPAm and HA-Fe-CYs particles can be used as drug delivery vehicles. Sulfamethoxazole (SMZ), an antibacterial drug, was used as a model drug for temperature-induced release studies from these particles.     

Polyimide/hollow silica sphere hybrid films with low dielectric constant

Abstract

Polyimide (PI)/hollow silica (HS) sphere hybrid films with low dielectric constant values (low-k) were synthesized via thermal imidization process using pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) as the polymer matrix and HS spheres as inorganic particles with the closed air voids. The monodispersed HS spheres were synthesized via a one-step process, which means that the formation of silica shells and dissolution of the core particles (polystyrene particles) occurs in the same medium. The HS particles have uniform size of ca. 1.5 μm in diameter and ca. 100 nm in shell thickness. PI/HS sphere hybrid films synthesized using mixture of polyamic acid (PAA) and HS spheres prepared via one-pot process, which means that the production of PAA and HS spheres mixture occurs with the polymerization of PMDA and ODA in the same bottle. HS spheres of two different kinds (pristine HS spheres (PHS spheres) and amine-modified HS spheres (AHS spheres)) were used for the preparation of the hybrid films. With the varying contents of AHS spheres in the range of 1–10 wt%, the dielectric constants of the PI/AHS sphere hybrid films were reduced from 3.1 of pure PI to 1.81 by incorporating 5 wt% AHS. The dielectric constants of the PI/PHS sphere hybrid films were reduced to 1.86 by incorporating 5 wt% PHS. Organic–inorganic hybrid porous polyimides may be expected as prime candidates for polymeric insulators due to their high thermal stability, good mechanical properties, solvent resistance, and low-k.     

Particle tracking microrheology of gel-forming amyloid fibril networks

Microrheology is a technique that is increasingly used to investigate the local viscoelastic properties of complex fluids non-invasively, by tracking the motion of micron-sized probe spheres. In this work, passive Particle Tracking Microrheology (PTM) is used to study network formation in the milk protein -lactoglobulin at 80 ^° C and p H 2. In these conditions the protein aggregates to form thread-like structures known as amyloid fibrils, which can further aggregate into elastic networks. Using PTM, gels were observed to form at significantly lower concentrations than determined by bulk rheometry, where the oscillatory shear forces may disrupt either fibril or network formation. During incubation, the Mean Square Displacement (MSD) of the probe particles exhibited time-cure superposition, allowing the critical relaxation exponent to be calculated as ∼ 0.63 , consistent with other biopolymer gels. Combined with the gel-like appearance of the complex modulus at long incubation times, this confirms that a true gel is forming, with physical or chemical crosslinks forming between the fibrils, refining the conclusions of other workers in the field.     

Preparation and structure analysis of nano-iron/mesocarbon microbead composites made from a coal tar pitch with addition of ferrocene

Nano-iron/mesocarbon microbead composites have been synthesized from a coal tar pitch by heating at 415 °C with ferrocene under pressure. The resulting composites were characterized using the combined techniques including SEM, TEM, XRD and EDS. The effect of ferrocene addition on the growth and structure of mesocarbon microbeads was discussed. It was found that nano-iron particles were of sizes 10-40 nm and mainly existed in the form Fe-O and Fe_1−xS. The iron particles, which had dispersed homogeneously in pristine and carbonized spheres, accelerated the nucleation and growth of spheres and consequently enhanced the structural ordering of spheres. The addition of ferrocene introduced a tendency to order in the microtexture of spheres.     

Rheology of nanosized hairy grain suspensions

Suspensions of nanosized hairy grains have been prepared by grafting long polydimethylsiloxane chains (molecular weight ) onto silica particles (radius ), dispersed into a good solvent of PDMS. Depending on the particle volume fraction, different rheological behaviors are observed. In the very dilute regime, the suspensions are perfectly stable and the particles behave almost as hard spheres: flow penetration inside the corona is then very weak. When the particle volume fraction goes to the close packing volume fraction, the suspension viscosity does not diverge as for hard spheres due to the increase of flow penetration inside the corona and to corona entanglements. The particles have then the same behavior as polymer stars having an intermediate number of arms (). Finally, in the concentrated regime (), the suspensions form irreversible gels. We shown that this unexpected gelation phenomenon is related to the presence of the silica cores: grafted PDMS chains can adsorb onto different particles and form irreversible bonds between the cores. The viscosity and elastic modulus evolutions during gelation are well described by the scalar percolation model of sol-gel transition. Received 23 March 1998     

The influence of radiation-induced vacancy on the formation of thin-film of compound layer during a reactive diffusion process

A theoretical approach is developed that describes the formation of a thin-film of AB-compound layer under the influence of radiation-induced vacancy. The AB-compound layer is formed as a result of a chemical reaction between the atomic species of A and B immiscible layers. The two layers are irradiated with a beam of energetic particles and this process leads to several vacant lattice sites creation in both layers due to the displacement of lattice atoms by irradiating particles. A- and B-atoms diffuse via these lattice sites by means of a vacancy mechanism in considerable amount to reaction interfaces A/AB and AB/B. The reaction interfaces increase in thickness as a result of chemical transformation between the diffusing species and surface atoms (near both layers). The compound layer formation occurs in two stages. The first stage begins as an interfacial reaction controlled process, and the second as a diffusion controlled process. The critical thickness and time are determined at a transition point between the two stages. The influence of radiation-induced vacancy on layer thickness, speed of growth, and reaction rate is investigated under irradiation within the framework of the model presented here. The result obtained shows that the layer thickness, speed of growth, and reaction rate increase strongly as the defect generation rate rises in the irradiated layers. It also shows the feasibility of producing a compound layer (especially in near-noble metal silicide considered in this study) at a temperature below their normal formation temperature under the influence of radiation.     

One-pot synthesis of uniform hollow cuprous oxide spheres fabricated by single-crystalline particles via a simple solvothermal route

Uniform Cu₂O hollow spheres fabricated by single-crystalline particles (smaller than 20 nm) are facile synthesized in ethylene glycol (EG) solution by a simple solvothermal route without using pre-fabricated templates and reductive agents. EG in this protocol is not only used as a solvent, complexing agent, and reducing agent, but also served as a structure-directing agent for the formation of hollow structure. By control of reaction conditions, such as reaction time, temperature, and the anions, the morphology and structure of the hollow spheres can be tuned. A coordination adsorption and oriented attachment and Ostwald ripening mechanism is proposed for explaining the formation process of hollow Cu₂O spheres in EG solution; and importantly, the hollow Cu₂O spheres exhibit an excellent property for the electro-catalytic oxidization of ascorbic acid in acetic acid buffer solution. Moreover, the hollow spherical Cu₂O particles could be potentially applied in catalysis, sensor, and as model for fundamental research.     

Self-Similar Asymptotics for the Boltzmann Equation with Inelastic and Elastic Interactions

We consider some questions related to the self-similar asymptotics in the kinetic theory of both elastic and inelastic particles. In the second case we have in mind granular materials, when the model of hard spheres with inelastic collisions is replaced by a Maxwell model, characterized by a collision frequency independent of the relative speed of the colliding particles. We first discuss how to define the n-dimensional (n = 1,2,...) inelastic Maxwell model and its connection with the more basic Boltzmann equation for inelastic hard spheres. Then we consider both elastic and inelastic Maxwell models from a unified viewpoint. We prove the existence of (positive in the inelastic case) self-similar solutions with finite energy and investigate their role in large time asymptotics. It is proved that a recent conjecture by Ernst and Brito devoted to high energy tails for inelastic Maxwell particles is true for a certain class of initial data which includes Maxwellians. We also prove that the self-similar asymptotics for high energies is typical for some classes of solutions of the classical (elastic) Boltzmann equation for Maxwell molecules. New classes of (not necessarily positive) finite-energy eternal solutions of this equation are also studied.     

Synthesis and luminescent properties of spindle-like YVO4:Ln3+ (Ln=Eu,Dy) self-assembled of nanoparticles

Large-scale spindle-like YVO₄ particles with an euatorial diameter of 100–150 nm and a length of 300–350 nm were synthesized by utilizing the Y(OH)CO₃ colloid spheres as the precursor and NH₄VO₃ as the vanadium source through a simple solution-based hydrothermal process, for the first time. In the first stage of the reaction, hierarchical flower-like YVO₄ spheres were formed. Then, petals of spindle-like YVO₄ particles were obtained via a following self-abscission process from these flower spheres. The possible formation mechanism has been discussed in detail. Moreover, the photoluminescent properties of spindle-like YVO₄:Ln³⁺ (Ln=Eu, Dy) nanoparticles were investigated. They might have potential application in advanced flat panel display, minioptoelectronic devices, and biological labeling.     

Nucleation and growth of SWNT: TEM studies of the role of the catalyst

This paper reviews transmission electron microscopy studies, combining high resolution imaging and electron energy loss spectroscopy, of the nucleation and growth of carbon single wall nanotubes with a particular emphasis on the nanotubes obtained from the evaporation-based elaboration techniques. Inspection of samples obtained from different synthesis routes shows that in all cases nanotubes are found to emerge from catalyst particles and that they have grown perpendicular or parallel to the surface according to whether they have been synthesized via evaporation-based methods or CCVD methods. Whereas the latter case corresponds to the well-known situation of carbon filaments growth, the former case strongly suggests another formation and growth process, which is described and its different steps discussed in detail. In this model, formation of the nanotubes proceeds via solvation of carbon into liquid metal droplets, followed by precipitation, at the surface of the particles, of excess carbon in the form of nanotubes through a nucleation and root growth process. It is argued that the nucleation of the nanotubes, which compete with the formation of graphene sheets wrapping the surface of the particle, necessarily results from a surface instability induced by the conditions of segregation. The nature and the origin of this instability was studied in the case of the class of catalyst Ni–R.E. (R.E.=Y, La, Ce, …) in order to identify the influence of the nature of the catalyst. The respective roles played by Ni and R.E. have been identified. It is shown that carbon and rear-earth co-segregate and self-assemble at the surface of the particle in order to form a surface layer destabilizing the formation of graphene sheets and providing nucleation sites for nanotubes growing perpendicular to the surface. To cite this article: A. Loiseau et al., C. R. Physique 4 (2003).     

Nano-sized silica hollow spheres: Preparation, mechanism analysis and its water retention property

In this article, synthesis of nano-sized silica hollow spheres applying positive charged polystyrene as sacrificial templates was introduced. Firstly, nano-sized polystyrene particles were synthesized by emulsifier-free emulsion polymerization under solvothermal condition. Secondly, silica hollow nanospheres were formed through a simultaneous ‘coating-etching’ process. PVP played a key role in the evolution of nano-sized hollow spheres even if the templates were positive charged and the formation mechanism was different from that of previous studies. TEM results revealed that the morphologies of nano-sized silica hollow spheres not only strongly relied on the amount of reactant, but also the sequence of adding them. TGA illustrated that the interiors of nano-sized silica hollow spheres were not completely ‘hollow’. Brunauer-Emmett-Teller (BET) analysis showed that this material had a specific area of 399 m²/g. The water retention property of the materials was also investigated.     

Synthesis, characterization and antibacterial action of hollow titania spheres

Hollow titania spheres were synthesized using the cationic polystyrene lattices which were prepared by polymerization in suspension of styrene using 2,2′-azobis (2-methylpropionamidine) dihydrochloride (AMPA) as an initiator. These cationic colloidal particles were dispersed in absolute ethanol in the presence of poly(vinylpyrrolidone) (PVP), solution of sodium chloride (NaCl) and mixed with ethanolic solutions of titanium tetraisopropoxide (TTIP). Subsequently, hollow spheres of titania compounds were obtained by calcinations of the so-coated polystyrene lattices at elevated temperature in air. The hollow titania spheres were characterized with scanning electron microscopy (SEM), FT-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Moreover, antibacterial action of illuminated hollow titania spheres on pure culture of Escherichia coli (E. coli) was studied. A decrease of E. coli concentration was observed after illumination of bacteria in the presence of hollow titania spheres.     

DDA simulations of light scattering by small irregular particles with various structure

We present DDA investigations of light scattering by irregular particles whose size is comparable with wavelength. We consider four types of randomly irregular particles: strongly damaged spheres, rough-surface spheres, pocked spheres, and agglomerated debris particles. Each type of particle is generated with a well defined algorithm producing an ensemble of stochastically different particles that have a common origin. The different types of irregular particles produce different angular dependencies of intensity and linear polarization degree. Transformation of phase curves of intensity and polarization with changing size parameter for irregular particles tends to be more monotonic, unlike spheres. We find that the magnitude of the negative polarization branch (NPB) tends to shrink as particle absorption increases; whereas, the maximal value and position of the positive polarization branch tends to increase. The most frequently observed shape of the negative polarization at small phase angles is asymmetric with a shift of the minimum position towards the angle of polarization sign inversion. All types of considered irregular particles reveal such asymmetry at x<10. Symmetric negative polarization branches occur seldom. The necessary conditions for their appearance are a relatively large size parameter x?10 to 12 and low absorption.     

On the growth mechanism and optical properties of ZnO multi-layer nanosheets

We report multi-layer ZnO nanosheets obtained by annealing Zn polyhedral particles in pure O₂. The structure comprises a cluster core with side faces terminated with 50-nm-thick multi-layer sheets. The nanosheets were found to be (0001)-oriented single-crystalline wurtzite ZnO. By studying the early growth stages, it appears that the sheets form through a ripening process of dendritic ZnO nanostructures, during which the single-crystalline nature and crystallographic orientation are conserved. The ripening is promoted by the rapid oxidation of the Zn polyhedral microcrystals. We also show that appropriate modification of the oxidation process leads to the formation of well-defined dendritic nanowires. The optical properties (photoluminescence and Raman) of these nanostructured materials are discussed. PACS 81.07.-b; 68.70.+w; 78.67.-n; 81.05.Dz; 68.37.-d     

Magnetic iron oxide nanoparticle-hollow mesoporous silica Spheres:Fabrication and potential application in drug delivery

A facile method is developed for the fabrication of magnetic iron oxide nanoparticle-hollow mesoporous silica spheres (IONP-HMSs) and explored their potential application in drug delivery. Through the self-assembling process of IONPs and the formation of mesoporous silica shells, the IONP-HMSs with hollow interior cavity were obtained. The cetyltrimethyl ammonium bromide (CTAB) encapsulated IONP-containing spheres served as the template to establish the mesoporous silica shells. Typical anti-cancer drug, doxorubicin hydrochloride (DOX) was applied for drug loading and release process of IONP-HMSs, which demonstrated the IONP-HMSs have a high drug loading efficiency and allow pH-trigged release of DOX in vitro. Moreover, the IONP-HMSs exhibited excellent biocompatibility and enhanced DOX therapeutic efficacy to HeLa cells. Compared with traditional methods, the reported microemulsion-based method for the synthesis of IONP-HMSs enables the formation of hollow-structured nanocomposite without any complex template-removing process, which could pave the way to improving the therapeutic efficacy in drug delivery system.     

Peculiarities of elastic scattering of intermediate-energy electrons related to their capture at quasi-stationary levels of an atom in a continuous spectrum

A theoretical model of electron scattering on an atom is constructed to study elastic atomic scattering of intermediate-energy electrons. The proposed model is based upon the combined Mensing potential with two spheres of atomic electrons, which admits analytical solutions of the radial Schröbinger equation. A procedure for matching the parameters of this scatterer to an approximate electrostatic potential of an atom in the form of a screened Coulomb potential has been determined. The screening radius of the latter potential has been calculated proceeding from the properties corresponding to the Thomas-Fermi method. A model of a scatterer determined according to the aforementioned procedure can be used to calculate the energy dependence of the cross section of elastic electron scattering on some atoms with s, p, and d shells representing elements neighboring zirconium. The main result is the establishment of factors responsible for the appearance of maxima on the energy dependences of the cross section of elastic electron scattering. These maxima are related to the resonant trapping of impinging electrons by quasi-stationary levels in a continuous spectrum.     

One injection for one-week controlled release: In vitro and in vivo assessment of ultrasound-triggered drug release from injectable thermoresponsive biocompatible hydrogels

Episodic release of bioactive compounds is often necessary for appropriate biological effects under specific physiological conditions. Here, we aimed to develop an injectable, biocompatible, and thermosensitive hydrogel system for ultrasound (US)-triggered drug release. An mPEG-PLGA-BOX block copolymer hydrogel was synthesized. The viscosity of 15 wt% hydrogel is 0.03 Pa*s at 25 °C (liquid form) and 34.37 Pa*s at 37 °C (gel form). Baseline and US-responsive in vitro release profile of a small molecule (doxorubicin) and that of a large molecule (FITC-dextran), from the hydrogel, was tested. A constant baseline release was observed in vitro for 7 d. When triggered by US (1 MHz, continuous, 0.4 W/cm²), the release rate increased by approximately 70 times. Without US, the release rate returned to baseline. Baseline and US-responsive in vivo release profile of doxorubicin was tested by subcutaneous injection in the back of mice and rats. Following injection into the subcutaneous layer, in vivo results also suggested that the hydrogels remained in situ and provided a steady release for at least 7 d; in the presence of the US-trigger, in vivo release from the hydrogel increased by approximately 10 times. Therefore, the mPEG-PLGA-BOX block copolymer hydrogel may serve as an injectable, biocompatible, and thermosensitive hydrogel system that is applicable for US-triggered drug release.     

Theory of multistep statistical decays in chains of genetically related nuclei

Systems of kinetic equations for decay chains of genetically related nuclei, the R-matrix theory of nuclear reactions with formation of unstable particles, and a diagram technique with Green’s function are used to study the general form for the widths of n-step statistical decays of parent nuclei that are in quasi-stationary resonance states. Conditions under which sequential and virtual decays occur are analyzed. Cases where interactions between particles emitted at different stages of processes must be allowed for are considered. Processes related to fissile nuclei that simultaneously emit three or more particles are discussed.     

ZnO spheres and nanorods formation: their dependence on agitation in solution synthesis

ZnO nanostructures including nanorods, dense, and partially hollow spheres were synthesized via a solution synthesis method with temperature ranging from 65 to 95 °C. Scanning electron microscopy (SEM) revealed that the diameter of the spheres is in the range of 200–500 nm. Transmission electron microscopy (TEM) showed that some of the spheres are hollow or partially hollow. Powder X-ray Diffraction (XRD) and TEM-Selected area electron diffraction (SAED) analysis showed that the spheres consist of polycrystalline nanoparticles. It was found for the first time that the agitation during the synthesis plays a critical role on morphology of the ZnO nanostructures formed in solution. The oriented attachment of nanocrystals without agitation during the synthesis could guide the nanocrystals to form an ordered nanorod structure. However, the disordered aggregation of the nanocrystals under shear force resulted in a spherical morphology. It was also found that the composition of spheres is different from that of nanorods: the spheres consist of both ZnO and Zn(OH)₂, but nanorods consist of single-crystal ZnO only. Zn(OH)₂ presented in the spheres could decompose to ZnO by calcination, resulting in the formation of hollow spheres.