Formation Of Submicron Particles Research Articles

Self-assembly/disassembly hysteresis of nanoparticles composed of marginally soluble, short elastin-like polypeptides

BackgroundElastin-like polypeptides (ELPs) are a fascinating biomaterial that has undergone copious development for a variety of therapeutic applications including as a nanoscale drug delivery vehicle. A comprehensive understanding of ELP self-assembly is lacking and this knowledge gap impedes the advancement of ELP-based biomaterials into the clinical realm. The systematic examination of leucine-containing ELPs endeavors to expand existing knowledge about fundamental assembly–disassembly behaviours.ResultsIt was observed that these marginally soluble, short ELPs tend to behave consistently with previous observations related to assembly-related ELP phase transitions but deviated in their disassembly. It was found that chain length, concentration and overall sequence hydrophobicity may influence the irreversible formation of sub-micron particles as well as the formation of multi-micron scale, colloidally unstable aggregates. Amino acid composition affected surface charge and packing density of the particles. Particle stability upon dilution was found to vary depending upon chain length and hydrophobicity, with particles composed of longer and/or more hydrophobic ELPs being more resistant to disassembly upon isothermal dilution.ConclusionsTaken together, these results suggest marginally soluble ELPs may self-assemble but not disassemble as expected and that parameters including particle size, zeta potential and dilution resistance would benefit from widespread systematic evaluations. This information has the potential to reveal novel preparation methods capable of expanding the utility of all existing ELP-based biomaterials.

Rapid precipitation of Mg-doped fluoride-based submicron spheres and evolution study

The present study investigates a rapid and template-free precipitation method for syntheses of Mg-doped fluoride based submicron spheres. The precipitates can be obtained less than one minute. The method also reveals the magnesium function in the formation of fluoride-based spherical submicron particles. The morphologies and structure changes of precipitates over time were studied via SEM and TEM. The surface bumps of Mg-doped BaF2 spheres disappeared after 4-h aging. Significant size increases of the particles have been observed. The evolution process during 4-h aging was typically Ostwald ripening.

Formation of ionic liquid submicron particles. 1H and 19F nuclear magnetic resonance spectroscopic studies

ABSTRACTWe prepared novel ionic liquid submicron particles (ILSPs) in water by emulsifying the ionic liquid (IL) N-(2-methoxyethyl)-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr12O1TFSI), which is immiscible with water, with the nonionic surfactants Tween 20 and Span 80. The mean particle size and zeta potential of the ILSPs were about 580 nm and −30 mV, respectively. The ILSPs were characterized using 1H and 19F nuclear magnetic resonance (NMR) spectroscopic methods. The chemical shifts of the Pyr12O1+ cation and TFSI− anion in the 1H and 19F NMR spectra of the ILSP suspension were consistent with those corresponding to pure Pyr12O1TFSI. This indicated that most of the Pyr12O1TFSI was still in the IL state in the ILSP suspension. In addition, 1H–1H nuclear Overhauser effect correlated spectroscopic measurements showed that the ILSP droplets contained Pyr12O1TFSI in the neat IL steric state even in the ILSP suspension, and Pyr12O1TFSI species localized in the droplet surfaces interacted with the hydrophobic acyl side chains of the surfactants. These NMR spectroscopic results show that the ILSPs formed an IL-in-water microemulsion in which droplets of neat Pyr12O1TFSI were surrounded by the two surfactants, that is, Tween 20 and Span 80.

Numerical simulation of submicron particles formation by condensation at coals burning

The thermodynamic analysis of the composition of the combustion products of 15 types of coals was carried out with consideration for the formation of potassium and sodium aluminosilicates and solid and liquid slag removal. Based on the results of the analysis, the approximating temperature dependences of the concentrations of condensed components (potassium and sodium sulfates) were obtained for the cases of two-phase and single-phase equilibriums; conclusions on the comparative influence of solid and liquid slag removal on the probability of the formation of submicron particles on the combustion of coals were made. The found dependences was make it possible to perform a numerical simulation of the bulk condensation of potassium and sodium sulfate vapors upon the cooling of coal combustion products in a process flow. The number concentration and size distribution of the formed particles have been determined. Agreement with experimental data on the fraction composition of particles has been reached at a reasonable value of a free parameter of the model.

Thermodynamic analysis of the formation of submicron particles on the combustion of coals

The thermodynamic analysis of the composition of the combustion products of 15 types of coals was carried out with consideration for the formation of potassium and sodium aluminosilicates and solid and liquid slag removal. Based on the results of the analysis, the approximating temperature dependences of the concentrations of condensed components (potassium and sodium sulfates) were obtained for the cases of two-phase and single-phase equilibriums; conclusions on the comparative influence of solid and liquid slag removal on the probability of the formation of submicron particles on the combustion of coals were made. The found dependences will make it possible to perform a numerical simulation of the bulk condensation of potassium and sodium sulfate vapors upon the cooling of coal combustion products in a process flow.

Nanoporous Au structures by dealloying Au/Ag thermal- or laser-dewetted bilayers on surfaces

Nanoporous Au attracts great technological interest and it is a promising candidate for optical and electrochemical sensors. In addition to nanoporous Au leafs and films, recently, interest was focused on nanoporous Au micro- and nano-structures on surfaces. In this work we report on the study of the characteristics of nanoporous Au structures produced on surfaces. We developed the following procedures to fabricate the nanoporous Au structures: we deposited thin Au/Ag bilayers on SiO2 or FTO (fluorine-doped tin oxide) substrates with thickness xAu and xAg of the Au and Ag layers; we induced the alloying and dewetting processes of the bilayers by furnace annealing processes of the bilayers deposited on SiO2 and by laser irradiations of the bilayers deposited on FTO; the alloying and dewetting processes result in the formation of AuxAgy alloy sub-micron particles being x and y tunable by xAu and xAg. These particles are dealloyed in HNO3 solution to remove the Ag atoms. We obtain, so, nanoporous sub-micron Au particles on the substrates. Analyzing the characteristics of these particles we find that: a) the size and shape of the particles depend on the nature of the dewetting process (solid-state dewetting on SiO2, molten-state dewetting on FTO); b) the porosity fraction of the particles depends on how the alloying process is reached: about 32% of porosity for the particles fabricated by the furnace annealing at 900 °C, about 45% of porosity for the particles fabricated by the laser irradiation at 0.5 J/cm2, in both cases independently on the Ag concentration in the alloy; c) After the dealloying process the mean volume of the Au particles shrinks of about 39%; d) After an annealing at 400 °C the nanoporous Au particles reprise their initial volume while the porosity fraction is reduced. Arguments to justify these behaviors are presented.

Catalytic conversion of 1,2-dichloroethane over Ni-Pd system into filamentous carbon material

The alloyed Ni-Pd system with Pd content of 3wt.% was prepared by coprecipitation method followed by reduction in hydrogen atmosphere at 800°C. The formation of single-phase solid solution with unit cell parameter a=3.532(1) Å (determined by (331) reflex at 2θ ≈ 145°) corresponding to NiPd alloy with weight ratio 97:3 was confirmed by XRD analysis. Kinetic studies on catalytic conversion of 1,2-dichloroethane (DCE) over NiPd alloy into carbon nanomaterial (CNM) were performed in a flow reactor equipped with McBain balances in a temperature range of 580–700°C. It was shown that interaction of DCE with NiPd system results in a fast disintegration of pristine alloy with formation of submicron (0.2-0.9μm) particles, which efficiently catalyze the growth of segmented carbon filaments. According to Raman spectroscopy and transmission electron microscopy data, hydrogen concentration in reaction mixture strongly affects the structural features and density of segmented filaments. The average values of inter-segmental distance calculated from TEM micrographs of carbon filaments were found to be 96, 46, 16nm for hydrogen concentration of 23, 36 and 47 vol.%, respectively. Strongly chemisorbed chlorine species were suggested to be responsible for the cyclic perturbations in carbon transfer and deposition. Obtained carbon nanomaterials were characterized with comparatively high specific surface area (300–400m2/g) and extremely low bulk density (<0.03g/ml).

Results from experimental studies of the formation of submicron particles during the destruction of solid bodies

A procedure for and the results from studies on directly estimating the size and number of submicron particles at the moment of the destruction and disintegration of solid bodies are described. Experiments require the breaking up of metallic rods or the crushing of rock samples subjected to uniaxial compression, and continuous monitoring of the size of particles by laser spectrometry. The formation of submicron particles with minimum sizes of ∼0.1 μm is observed. The size distribution and number of these particles depend on the structural and physical parameters of the solid bodies.

Properties of arsenic sulphide (β-As4S4) modified by mechanical activation

Arsenic sulphide β-As4S4 has been modified by mechanical activation in a planetary ball mill. As a consequence, the solid-state properties and dissolution yield have been influenced. The following changes were observed: the increase of specific surface area, changes in the morphology (the formation of submicron particles), the occurrence of nanoparticles (21–31 nm), changes in crystal lattice parameters and changes in the Raman shift of particular vibrations. As a consequence of these changes, the dissolution rate of β-As4S4 has been increased, which is a challenge for the application in cancer research.

Experimental regularities in formation of submicron particles under rock failure

Based on the developed procedure, experimental regularities are obtained for the formation of submicron particles under rock failure. The experiments involved explosion load on rock specimens and their uniaxial compression with the concurrent control over size and amount of particles until failure using laser spectrometry. It is found that most of all particles are formed in the size grade of a few microns irrespective of the kind of loading. Dynamics of the formation of particles depends on structural characteristics of specimens and on the value of the compression stress. The authors emphasize the promising nature of the experimental results usable both in the environmental monitoring and for disaster prediction in the course of mining.

Organized Polymeric Submicron Particles via Self-Assembly and Cross-Linking of Double Hydrophilic Poly(ethylene oxide)-b-poly(N-vinylpyrrolidone) in Aqueous Solution

The formation of submicron particles consisting of double hydrophilic diblock copolymers of poly(ethylene oxide) and poly(N-vinylpyrrolidone) (PEO-b-PVP) in aqueous solution is described. Block copolymers were synthesized via reversible deactivation radical polymerization using a PEO-xanthate as macro RAFT/MADIX chain transfer agent. Increasing polymer concentrations in aqueous solutions, the block copolymer is able to self-assemble into spherical structures with apparent hydrodynamic diameters in the range between 200 nm and 2 μm. The self-assembly was further improved by copolymerization with a more hydrophilic monomer, N-vinylimidazole (VIm). Submicron particles from PEO-b-P(VP-co-VIm) were preserved via cross-linking utilizing imidazolium formation with a dihalogenide. Thus, submicron double hydrophilic particles were obtained that are stable in organic solvents and under high dilution. Almost quantitative formation of submicron particles with an average diameter of 200 nm can be afforded by the self-assembly in the polar organic solvent DMF and subsequent crosslinking as well. Furthermore, the obtained particles show a promising ability to incorporate various molecules for delivery and release, here exemplified with simple dyes.

Impact of rapid expansion of supercritical solution process conditions on the crystallinity of poly(vinylidene fluoride) nanoparticles

The rapid expansion of supercritical solution (RESS) process was used to produce poly(vinylidene fluoride) (PVDF) nanoparticles. PVDF was chosen since five different crystal phases (α, β, γ, δ, ε) have been reported in literature. The experiments were performed with a low molar mass polymer (Mn=1500gmol−1) that consists exclusively of α phase. The main objectives of this study were to examine the influence of process parameters, i.e. inner nozzle diameter, pre-expansion temperature and pressure on polymer crystallinity and crystal phase properties. Before and after micronization, the polymer was characterized by scanning electron microscopy, size-exclusion chromatography, differential scanning calorimetry and X-ray diffraction.The findings of our investigations clearly show that RESS enables the formation of submicron particles. Furthermore, under certain process conditions, i.e. higher expansion and cooling rates and thus small nozzle diameters, RESS induces a crystal phase transformation from α to the desired β phase. In opposite thereto, simple static treatment with scCO2 does not induce crystal phase transformation. Furthermore, average molar mass, dispersity and crystallinity of the RESS product was reduced due to the preferred extraction of low molar mass fractions.

Simulation of parameters of submicron particles formed in combustion products of coals

Thermodynamic analysis of the composition of combustion products have been performed for 15 types of coals with and without allowance for potassium and sodium aluminosilicates. Based on the results obtained, a closed model has been proposed for the formation of submicron particles in the combustion products of the coals, which enables one to obtain the upper estimate for the content of submicron particles in these products. The bulk condensation of potassium sulfate vapor in the flow of the combustion products and upon their cooling along a technological path has been numerically simulated by means of computer-assisted realization of the proposed model. The number concentration and size distribution of the formed particles have been determined. Agreement with experimental data on the average particle size has been reached at a reasonable value of a free parameter of the model.

Microstructural characteristics and second-phase particles in yttrium-bearing Fe-10Ni-7Mn martensitic steels

In this study, the microstructure and second-phase particles in yttrium (0.05 wt.% and 0.8 wt.%) bearing Fe-10Ni-7Mn steels were characterized. The results of X-ray analysis as well as scanning electron microscopy coupled with energy dispersive X-ray spectroscopy indicated the formation of (Fe, Ni, Mn)17Y2 precipitates with hexagonal structure in a Fe-10Ni-7Mn-0.8Y (wt.%) alloy. Lattice parameters of these precipitates were calculated as follows: a=0.8485 nm and c=0.8274 nm. Formation of Y2O3 sub-micron particles was also confirmed in both yttrium bearing steels via electrolytic phase extraction method. The effect of these precipitates on the prior austenite grain size was investigated. The results revealed that these precipitates had an effective role in controlling the prior austenite grain size.

Development of a system by atomization for the formation of polymeric particles in micro and sub-micro scales

Several studies in nanotechnology have demonstrated significant advantages of nanoparticles compared with microparticles. The main reason for this is the higher ratio of surface area per volume, which results in specific characteristics. Such considerations have driven researchers to develop techniques to obtain polymeric nanoparticles with properties that allow application in different areas. The objective of this work is to present a polymerization process by atomization applied to miniemulsion and suspension systems for formation of submicron particles of poly(methyl methacrylate) (PMMA) and polystyrene (PS). Reactions were carried out using the proposed technique and polymeric particles were obtained with size between 40 and 300nm, according to dynamic light scattering (DLS) analysis, and with spherical morphological characteristics, according to the results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Structural phase transformations in tin dioxide under the action of a nanosecond high-power ion beam

Structural phase transformations in polycrystalline tin dioxide under the action of a nanosecond high-power ion beam with a current density of 50–150 A/cm2 are studied. It is found that the effect of a beam with a current density of 150 A/cm2 on SnO2 leads to the formation of submicron particles of tetragonal SnO with an average size of 210 nm on the exposed surface. The particles have a pronounced crystallographic facet pattern. Possible mechanisms of the observed transformations are discussed.

Microwave mediated preparation of nanoparticles from wx corn starch employing nanoprecipitation

The influence of alkali concentration, temperature, concentration of urea and KSCN on the shapes and sizes of wx corn starch precipitates (isolated via nanoprecipitation) were studied. A strong correlation was found between the molecular and hydrodynamic characteristics, determined by using asymmetrical flow‐field flow fractionation (AF4), and the resultant sizes of micro‐ and nanostructures of wx corn starch precipitates (SEM images). Treatment of wx corn in alkaline media at higher temperatures employing a dedicated microwave reactor resulted in the formation of submicron particles (SEM analysis). The apparent molecular characteristics of wx corn starch heated in 1 M NaOH at various temperatures employing a microwave reactor, decreased with increasing temperature and with a corresponding decrease in particle sizes (SEM images of the precipitates). An expansion and decrease in the overall densities of the starch structures was observed for wx corn in 1 M urea, 0.2 M NaOH at 130°C resulting in smaller particle sizes.

The formation of submicron particles in mining and a new method of assessing catastrophic phenomena

The topic of this article offered for the reader’s attention is the study of destruction processes in rocks at the micro- and nanolevels. The author presents his original technique and experimental studies on the quasi-static loading of rock samples for predicting predestruction states.

Effects of Submicron Particles on Formation of Micron-Sized Particles During Long-Term Storage of an Interferon-Beta-1a Solution

<h2>ABSTRACT</h2> We present evidence that homogeneous submicron particles can influence the growth rate of larger particles upon long-term storage in a temperature-dependent manner. Interferon-beta-1a was thermally stressed at 50°C for 6h and characterized using nanoparticle tracking analysis (NTA), microflow digital imaging (MFI), and circular dichroism (CD) spectroscopy. This study showed selective formation of submicron particles exhibiting a perturbed protein conformation. These thermally induced submicron particles were spiked into an unstressed solution at three levels, and then monitored for micron-sized particle formation upon storage at 5°C and 25°C for 12 months. The resulting particle growth effects were temperature dependent. NTA and MFI results at 5°C showed little evidence that initial submicron particle levels impacted particle growth across the range ~0.03–25 μm. In contrast, MFI results at 25°C indicated that particle growth in the 1–10 μm size range correlated strongly with initial submicron particle levels, and particle counts in the 10–25 μm size range were highest after 12 months for the samples with highest initial submicron particle content. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:347–351, 2013

From NH4TiOF3nanoparticles to NH4TiOF3mesocrystals: steric hindrance versus hydrophobic attraction of F127 molecules

The formation of NH4TiOF3 mesocrystals can be largely manipulated by controlling the colloidal and chemical stabilities of NH4TiOF3 nanoparticles as the building blocks. The factors studied in the present work are temperature and the concentration of F127 (a triblock copolymer). At 23 °C and 35 °C, the presence of 10% F127 gives rise to the formation of submicron particles, whereas, a lower concentration of F127 results in submicron particles and aggregates, and a higher concentration produces a combination of NH4TiOF3 mesocrystals and submicron particles. The process is dominated by the formation of NH4TiOF3 mesocrystals at 4 °C, where the chemical conversion from NH4TiOF3 nanoparticles to TiO2 nanoparticles is significantly slowed down. A pancake-like conformation of F127 molecules on the hydrophilic particle surfaces is adopted to explain the concentration dependent steric effect and hydrophobic attraction imparted by their PPO chains. The TiO2 nanocrystals derived from calcination show superior photocatalytic performance, in comparison to TiO2 mesocrystals, due to the much higher specific surface area.