Dispersion Mechanism of Superfine SiC Particles in the Different Condition Liquid

SiC@A1(OH)₃-Y(OH)₃ core-shell composite particles are synthesized by co-precipitation method for strengthening the antioxidation of SiC at high temperature. To reach better A1(OH)₃-Y(OH)₃ composite shell and higher coating ratio on the SiC particles surfaces, SiC particles must be adequately dispersed in the SiC suspension during the coating process. The dispersion mechanism of SiC particles is investigated by the sedimentation method. Through test and analysis, the optimum conditions of the dispersion of SiC particles in the SiC suspension are sedimentating for 10 minutes, ultrasonic dispersion for 10 minutes, the lower SiC concentration, pH = 9, the dispersant content for the 2% volume of SiC suspension and using the polyelectrolyte dispersant, respectively.     

The State of NaOH in NaOH/Poly(Sodium Acrylate) Composite

NaOH/poly(sodium acrylate) composites were prepared by in situ polymerization of acrylic acid with an overneutralization level by adding excess NaOH. The composites were studied by XRD, IR and ²³Na MAS NMR spectroscopy. The results showed that the high neutralization degree (>100%) may lead to a complete polymerization. Both XRD and ²³Na MAS NMR spectra did not show any peaks of phase-separated NaOH or Na₂CO₃ until the neutralization degree was up to 217.5%. It can be presumed that the aggregates of Na⁺ ions can contain approximately two Na⁺ units for every carboxyl group before the phase separation.     

Polymer colloids formed by polyelectrolyte complexation of vinyl polymers and polysaccharides in aqueous solution

The polyelectrolyte complex formed from the polyanion and polycation was studied by turbidimetry, static and electrophoretic light scattering, and elementary analysis. Sodium salts of polyacrylate (PA) and heparin (Hep) were chosen as the polyanion, and hydrochloric salts of poly(vinyl amine) (PVA) and chitosan (Chts) as the polycation. Although these vinyl polymers and polysaccharides have remarkably different backbone chemical structures and linear charge densities, all the four combinations PA-PVA, PA-Chts, Hep-PVA, and Hep-Chts provide almost stoichiometric polyelectrolyte complexes which are slightly charged owing to the adsorption of the excess polyelectrolyte component onto the neutral complex. The charges stabilize the complex colloids in aqueous solution of a non-stoichiometric mixture, and the aggregation number of the complex colloids increases with approaching to the stoichiometric mixing ratio. The mixing ratio dependence of the aggregation number for the four complexes is explained by the model proposed in the previous study.     

Dielectric properties of liquid crystalline composites doped with nano-dimensional fragments of shungite carbon

A cholesteric liquid crystal (CLC) – cholesteryl tridecylate (X-20) was doped with nanoparticles of shungite carbon (Sh) to effectively improve some physicochemical properties of the CLC matrix for the further use in electronic devices. The influence of Sh (concentration of 0.005 and 0.02 wt. %) on phase transition temperatures of X-20 was studied. Addition of 0.005 wt. % of Sh shifts phase transition temperatures upward, while the concentration increase to 0.02 wt. % leads to the opposite effect. These data were taken into account during the study of dielectric properties in different phase states. The dielectric properties were studied in the frequency range from 20 Hz to 10 MHz. Only for the system X-20/Sh (0.02 wt. %), dispersion of the dielectric permittivity was observed. The dispersion was caused by the appearance of additional relaxation processes and it was substantially more extended than the classical Debye theory suggests. The results of the research show that the ‘CLC – Sh nanoparticles’ composites can be used as promising materials to increase the efficiency of radio electronics devices.     

Stable aqueous dispersion of magnetic iron oxide core–shell nanoparticles prepared by biocompatible maleate polymers

A new method is applied to prepare stable aqueous dispersion of magnetic iron oxide nanoparticles (MNPs) by biocompatible maleate polymers. Fe₃O₄ magnetic core–shell nanoparticles are obtained via forming an inclusion complex between carboxylic acid groups of maleated biocompatible polymers shell and Fe₃O₄ MNPs core surface. Maleate polymers are synthesized via esterification of poly(ethylene glycol), poly(vinyl alcohol) and starch with maleic anhydride (MA). The Fe₃O₄ magnetic core–shell nanoparticles are characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The obtained magnetic core–shell nanoparticles exhibit superparamagnetic property and reveal long‐term aqueous stability. This work represents a valid methodology to produce highly stable aqueous dispersion of Fe₃O₄ MNPs ferrofluids which can be expected to have great potential as contrast agent for magnetic resonance imaging. Furthermore, the shell composition of biocompatible maleate polymers with double bond of MA as crosslinker agent allows the polymerization with other monomers to design preferred drug delivery systems. Copyright © 2014 John Wiley & Sons, Ltd.     

An improved capillary electrophoresis method for in vitro monitoring of the challenging early steps of Aβ1–42 peptide oligomerization: Application to anti‐Alzheimer's drug discovery

We report an improved CE method to monitor in vitro the self‐assembly of monomeric amyloid β‐peptide (42 amino acids amyloid β‐peptide, Aβ_1–42) and in particular the crucial early steps involved in the formation of the neurotoxic oligomers. In order to start the kinetics from the beginning, sample preparation was optimized to provide samples containing exclusively the monomeric form. The CE method was also improved using a dynamic coating and by reducing the separation distance. Using this method, the disappearance of the monomer as well as the progressive formation of four species during the self‐assembly process can now be monitored and quantified over time. The hydrodynamic radius of the species present at the initial kinetics step was estimated around 1.8 nm by Taylor dispersion analysis while SDS‐PAGE analyses showed the predominance of the monomer. These results confirmed that the Aβ_1–42 species present at this initial time was the monomer. Methylene blue, an anti‐Alzheimer disease candidate, was then evaluated. In spite of an oligomerization inhibition, the enhanced disappearance of the Aβ_1–42 monomer provoked by methylene blue was demonstrated for the first time. This method, allowing the monomeric and smallest oligomeric species to be monitored, represents a new accurate and precise way to evaluate compounds for drug discovery.     

Kinetics of radical‐molecule reactions in aqueous solution: A benchmark study of the performance of density functional methods

The performance of 18 density functional approximations has been tested for a very challenging task, the calculations of rate constants for radical‐molecule reactions in aqueous solution. Despite of the many difficulties involved in such an enterprise, six of them provide high quality results, and are recommended to that purpose. They are LC‐ωPBE, M06‐2X, BMK, B2PLYP, M05‐2X, and MN12SX, in that order. This trend was obtained using experimental data as reference. The other relevant aspects used in this benchmark are: (i) the SMD model for mimicking the solvent; (ii) the conventional transition state, the zero‐curvature tunneling correction, and the limit imposed by diffusion for the calculation of the rate constants. Even though changing any of these aspects might alter the trend in performance, at least, when using them, the aforementioned functionals can be successfully used to obtain high quality kinetic data for the kind of reactions investigated in this work. © 2014 Wiley Periodicals, Inc.     

Formation of Hexagonally Packed Hollow Hoops and Morphology Transition in RAFT Ethanol Dispersion Polymerization

Similar to the traditional self‐assembly strategy, polymerization induced self‐assembly and reorganization (PISR) can produce a myriad of polymeric morphologies through morphology transitions. Besides the chain length ratio (R) of the hydrophobic to the hydrophilic blocks, the chain mobility in the intermediate nano‐objects, which is a requisite for morphology transition, is a determining factor in the formation of the final morphology. Although various morphologies have been fabricated, hexagonally packed hollow hoops (HHHs) with highly ordered internal structure have not, to the best of our knowledge, been prepared by PISR. In this article, the fabrication of HHHs through morphology transition from large compound vesicles to HHHs is reported. HHHs with highly regular internal structure may have significance in theoretical research and practical applications of nanomaterials.