A polymer in an ionic liquid: Structural properties of a system during attraction between the polymer and cations of the ionic liquid

In terms of the polymer integral equation theory, structuring in ionic liquids containing flexiblechain polymers under the conditions of good solubility is studied for the first time. The influence of the polymer concentration on the structural properties of system components is studied at different lengths of polymer molecules. The structural organization of the ionic liquids is shown to be fairly stable after addition of the polymer. When there is attraction between the polar groups of cations of the ionic liquid and polymer molecules, the calculated structural factors suggest intermediate-range scales of polymer-component ordering. Given this, for any considered length of polymer molecules, there is a range of polymer concentrations in which the characteristic scale of ordering decreases with an increase in polymer density according to a power law.     

Nanoscale morphology in sulphonated poly(Ether ether ketone)-based ionomeric membranes: Mesoscale simulations

The model of a proton-conducting membrane based on sulfonated aromatic poly(ether ether ketone) has been constructed in the context of the mesoscale-dynamics method. The structure of the polymer is represented as a linear adjusted sequence of polar and nonpolar chain units. The degree of sulfonation and water content in the system are the main parameters during calculations. The constructed model shows that microphase separation of hydrophilic and hydrophobic polymer chain units occurs even at small water contents. A spatial network of water domains that has walls made of polymer-matrix polar chain units is formed within the membrane volume. The estimation of the percolation threshold demonstrates that water domains form a penetrating system of channels at water contents as low as 5–9%. Analogous simulations have been performed for the well-studied Nafion-1100 membrane. Although the morphologies of hydrophilic channels in sulfonated aromatic poly(ether ether ketone) and Nafion differ substantially, their cross sections are close. The results make it possible to consider sulfonated aromatic poly (ether ether ketone) a possible alternative to Nafion during the development of proton-conducting membranes for new-generation fuel cells.     

Structure, phase transitions, 55Mn NMR, and magnetoresistive properties of La0.6Sr0.2Mn1.2 ? yCryO3 ± δ

The structure and properties of lanthanum strontium manganite perovskites La_0.6Sr_0.2Mn_{1.2 − y} Cr _y O_{3 ± δ} (y = 0–0.3) sintered at 1430°C have been studied by X-ray, resistive, and magnetic (χ_ac and ⁵⁵Mn NMR) methods. The parameter of the rhombohedrally distorted (R $ \bar 3 $ \bar 3 c) perovskite structure decreases with increasing y. The real perovskite structure contains point (anion and cation vacancies) and cluster-type nanostructure defects. The analysis of asymmetrically broadened ⁵⁵Mn NMR spectra has confirmed the high-frequency electron-hole exchange Mn³⁺ ↔ Mn⁴⁺ and local inhomogeneity of their surrounding by other ions and point and cluster-type defects. An increase in the Cr content leads to an increase in the resistivity and the magnetoresistive effect and a decrease in the metal-semiconductor and ferromagnetic-paramagnetic phase transition temperatures (T _ms and T _c ) due to the distortion of the exchange interactions Mn³⁺ ↔ Mn⁴⁺ by chromium ions, vacancies, and clusters. Introduction of Cr decreases the ferromagnetic component and increases the activation energy. The magnetoresistive effect near T _ms and T _c is caused by scattering of charge carriers from intercrystallite nanostructure inhomogeneities of the lattice, and the low-temperature effect is associated with the tunneling on mesostructural intercrystallite boundaries.     

A supramolecular medical hydrogel based on <Emphasis Type="Italic">L</Emphasis>-cysteine and silver ions

A novel supramolecular thixotropic gel based on low-concentration aqueous solutions of L-cysteine and silver nitrate is synthesized. Self-organization and gel formation in the system of interest is studied by means of UV and IR spectroscopy, transmission electron microscopy, dynamic light scattering, and rotational viscometry. A model of the supramolecular gel is suggested. Possible applications for medicinal purposes are considered.     

A repeat electron diffraction study on the structures of WCl3, W2Cl6, and WCl4

High-Temperatures Institute, USSR Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 1, pp. 49–55, January–February, 1990.     

Quartz crystal microbalance simulation of the directionality of Si etching in CF4 glow discharges

Two quartz crystal microbalances have been mounted in a planar rf discharge system in such a way that the potential of the microbalances with respect to the glow discharge can be varied. This apparatus allows a rapid simulation of the etching directionality that can be expected in real pattern transfer situations in that operating one microbalance at ground and one at a negative potential gives a measure of the sidewall and vertical etch rates, respectively. The voltage threshold for ion-assisted etching has been determined to be 20 V which is the approximate value of the plasma potential in this asymmetric system.     

Formation of x-ray beams with the aid of a tapered microcapillary

The possibility of obtaining x-ray microbeams with a prescribed intensity using a system containing a x-ray tube with a transmission thin-film anode and a tapered glass microcapillary is investigated. Zh. Tekh. Fiz. 68, 90–93 (May 1998)