Amino Acid-Functionalized Calix[4]Resorcinarene Solubilization by Mono- and Dicationic Surfactants

Poorly water-soluble calix[4]resorcinarenes modified with amino acid (Ala, Val) at the upper rim formed a water-soluble mixed system with micelles of monocationic surfactants cetyltrimethylammonium bromide, cetyldimethyl(2-hydroxyethyl)ammonium bromide, and dicationic (gemini) surfactants, alkanediyl-α,ω-bis(dimethyltetradecylammonium bromides (14-s-14, where s = 2, 4, or 6). UV–Vis and DLS methods demonstrated that the micellar systems of surfactant/functionalized calix[4]resorcinarene underwent structural changes within a relatively narrow concentration range followed by changes in solubilization capacity and polydispersity. Gemini surfactants and monocationic/gemini mixed surfactant systems were provided selectivity in their interaction with calix[4]resorcinarene depending on the bulkiness of the substituent at the upper rim of calix[4]resorcinarene, gemini surfactant spacer length, and mixed micelles. These systems represent a direction to create biocompatible water-soluble functionalized calix[4]resorcinarene composition and may open perspectives in designing organized systems with controllable properties.     

The problem of optimal technologies for functional materials

The work analyzes the possibility of treating the production of a functional material as the realization of the stage of separation of the substance forming the material from a supersaturated medium and the stages of physical and chemical modification of the separated substance. The key kinetic equation of variation of the distribution function of states of the particles of the substance at each stage is formulated, considering the discrete nature of the nucleation, growth, and aggregation of particles. Solutions to continuous versions of the kinetic equation with regard to each stage are given. The conception of the path $ \vec Z(\vec g) $ of obtaining the material is introduced in the form of the coupling function of the target properties $ \vec Z $ of the compound with characteristics $ \vec g $ } of the reactors where the material is produced. The conditions are considered under which the path can be regarded as optimal at each stage, and the optimality criteria of the routes are introduced.     

Effect of phase velocity nonequilibrium on flame propagation and extinction

The problem of flame propagation in the presence of inert particles is considered. The mathematical model used is based on the equations of the mechanics of multiphase media in a two-temperature, two-velocity approximation. Numerical calculations of combustion in the presence of a dispersed phase in zero gravity show that the flame does not quench. For flame propagation in the gravity field directed toward falling particles, a new phenomenon, namely, flame quenching, is revealed. It is shown that the quenching is due to the occurrence of feedback between the flame velocity and the magnitude of heat losses. Critical parameters for various values of the external mass force and particle size are determined.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 3, pp. 11–23, May–June, 1996.     

Development of heating elements based on conductive polymer composites for electrofusion welding of plastics

Conductive polymer composites have been developed based on high-density polyethylene filled with carbon black (HDPE-CB), capable of generating heat when an electric voltage is applied. For each voltage value, the composite reached a constant value of equilibrium temperature, which obeyed a quadratic dependence on voltage and a linear dependence on electric power. The possibility of using such composites as heating elements (HE) for electrofusion welding of polyethylene adherents was evaluated in two modes, ''hard'', when high voltage was applied for a short welding time, and ''soft'', in which a stepwise regime of the applied voltage and a longer welding time were used. The latter provided a stronger welded joint. Using HE based on the HDPE-CB composites for welding of butt and lap joints of the polymer materials enabled to obtain welded joints with high strength.     

Supramolecular Systems Based on Novel Amphiphiles and a Polymer: Aggregation and Selective Solubilization

Supramolecular systems based on novel triazole-containing and pyrimidine-containing amphiphiles bearing OH-groups and a hydrophilic polymer (polyethyleneimine, PEI) were fabricated. Aggregation threshold of individual amphiphile solutions and a surfactant/polymer binary mixture were determined to be equal to 2 and 0.05 mM, respectively, using tensiometry and conductometry techniques. It was found, that PEI addition to surfactant aqueous solutions induces the transition from open to closed association mode accompanying the decrease of mean hydrodynamic diameter of particles (D _H) from 100 nm to D _H ≤ 5 nm. Polymer addition to the system results in the leveling of pH decrease with surfactant concentration and increase of the electrokinetic potential values from 10 mV up to 40 mV. It was established that solubilization capacity of the supramolecular system formed could be increased by transition from surfactant individual solutions to the amphiphile/polymer binary system. The solubilization properties of the system strongly depend on the nature of the hydrophobic guest solubilized and differ by two orders of magnitude for hydrophobic azodye and lipophilic oxime.     

Tubular alumina as a key component of new thermally stable ceramic materials

Using scanning electron microscopy and X-ray diffraction, we have examined processes that occur in tubular alumina during heating in air to temperatures in the range 1100–1200°C. The results demonstrate that, starting at temperatures between 600 and 700°C, α-Al₂O₃ (corundum) is formed in the solid material. Heating the tubular material to 1000°C converts some of the starting alumina into χ-Al₂O₃ and some into α-Al₂O₃. The samples calcined for 2–10 h at 1100°C contain α-Al₂O₃ and æ-Al₂O₃. Heating to 1000–1300°C has no effect on the shape of the tubular particles. The ceramics obtained in this way are stable in contact with water. When tubular alumina with a SiCl₄ vapor hydrolysis product deposited on its surface is heat-treated at temperatures in the range 1100–1300°C, we observe the formation of mullite (Al₂O₃ · 2SiO₂) on the surface of the tubular particles.     

Higher-order and higher floating-point precision numerical approximations of finite strain elasticity moduli

Two real-domain numerical approximation methods for accurate computation of finite strain elasticity moduli are developed and their accuracy and computational efficiency are investigated, with reference to hyperelastic constitutive models with known analytical solutions. The methods are higher-order and higher floating-point precision numerical approximation, the latter being novel in this context. A general formula for higher-order approximation finite difference schemes is derived and a new procedure is proposed to implement increased floating-point precision. The accuracy of the approximated elasticity moduli is investigated numerically using higher-order approximations in standard double precision and increased quadruple precision. It is found that, as the order of the approximation increases, the elasticity moduli tend toward the analytical solution. Using higher floating-point precision, the approximated elasticity moduli for all orders of approximation are found to be more accurate than the standard double precision evaluation of the analytical moduli. Application of the techniques to a finite element problem shows that the numerically approximated methods obtain convergence equivalent to the analytical method but require greater computational effort. It is concluded that numerical approximation of elasticity moduli is a powerful and effective means of implementing advanced constitutive models in the finite element method without prior derivation of difficult analytical solutions.     

Controlling the Placement of Spherical Nanoparticles in Electrically Driven Polymer Jets and its Application to Li‐Ion Battery Anodes

Employing circumferentially uniform air flow through the sheath layer of the concentric coaxial nozzle, the gas‐assisted electrospinning (GAES) utilizes both high electric field and controlled air flow to produce nanofibers. The ability to tailor the distribution of various nanofillers (1.85–12.92 vol% of spherical SiO₂ and Si nanoparticles) in a polyvinyl alcohol jet is demonstrated by varying airflow rates in GAES. The distribution of nanofillers is measured from transmission electron microscopy and is analyzed using an image processing technique to perform the dispersion area analysis and obtain the most probable separation between nanoparticles using fast Fourier transform (FFT). The analysis in this study indicates an additional 350% improvement in dispersion area with the application of high but controlled airflow, and a 75 percent decrease in separation between nanoparticles from the FFT. The experiments in this study are in good agreement with a coarse‐grained MD simulation prediction for a polymer nanocomposite system subjected to extensional deformation. Lastly, utilizing the sheath layer air flow in production of Li‐battery anode material, a 680 mAh g^?1 improvement is observed in capacity for nanofibers spun via GAES compared to ES at the same Si NP loading, which is associated with better dispersion of the electrochemically active nanoparticles.     

Numerical simulation of hydrogen evolution upon interaction between zirconium melt and water

The process of hydrogen generation upon interaction between a zirconium melt and water is studied. An oxidation model for zirconium liquid droplets in a water–steam medium was developed. The model was incorporated into the VAPEX computational code developed for calculation of interactions between core material melts and water during a severe accident at nuclear power plants equipped with pressurized water reactors. The modified VAPEX code was used to analyze the ZREX experiments on molten zirconium–water interactions. It was shown that the VAPEX code satisfactorily predicts the amount of the hydrogen generated during such an interaction.