Specific Features of Cellulose Phase Transition via Knecht Additive Compound

The capability of cotton and wood cellulose in the common and microcrystalline forms to transform into cellulose-II under the action of 68-69% HNO₃ was studied. The influence of temperature on the course of the phase transition in cellulose samples differing in origin and morphological structure and the dynamics of concomitant hydrolytic degradation and esterification of these materials were studied.     

Combination of oxidative and hydrolytic functions of nitric acid in production of enterosorbents based on carboxylated microcrystalline cellulose

A single-stage procedure was developed for preparing carboxylated microcrystalline cellulose from native cellulose in 45–55% nitric acid acting as a deposited form of catalyst of cellulose oxidation, nitrogen(IV) oxide, and as a selective reagent partially hydrolyzing cellulose.     

Sulfation of polysaccharides with sodium pyrosulfate in dimethyl sulfoxide

Sulfo esters of cellulose, dextran, starch, and amylopectin with a degree of substitution equal to 0.1–1.1 were prepared in the system constituted by sodium pyrosulfate and dimethyl sulfoxide. The intrinsic viscosity of aqueous solutions of sulfo polysaccharides was determined, and their anticoagulant activity was evaluated.     

Nanoelectronic Devices Based on Carbon Nanotubes

We review the state-of-the-art in the carbon nanotube (CNT) electronics. The emphasis is made on actually created devices. The history of discovery of fullerenes is outlined and their properties are considered. Experimental discovery of nanotubes and nanotube synthesis technologies are reviewed. The CNT conductivity dependence on the geometrical structure of nanotubes is discussed. Various nanoelectronic CNT devices, such as nanowires, heterojunctions, diodes, and field-effect transistors are presented. Quantum properties of CNTs at low temperatures are discussed. CNT-based mechanical devices, memory elements, and switches are considered. Field emission properties of CNTs are analyzed. The data on the developed CNT-based light-emitting elements and the manufactured pre-production models of CNT flat-panel displays are given.     

Preparation and Properties of Enterosorbents Based on Carboxylated Microcrystalline Cellulose

Features of a non-traditional method of preparation of cellulose-based cation-exchange enterosorbents using nitrogen (IV) oxide are discussed. The proposed approach involves sequential use of oxidative and acid-hydrolyzing functions of nitrogen (IV) oxide to convert ordinary cellulose into carboxylated microcrystalline cellulose. X-ray phase analysis and transmission electron microscopy data show evidence of a topochemical character of cellulose microcrystal modification with carboxyl groups. Factors are indicated causing enhanced stability and whiteness of the samples thus obtained as compared with oxidized cellulose fibres, as well as the ease of stable tixotropic gel formation from the samples prepared in a salt form. Exemplified by methylene blue sorption, a comparative assessment of the sorptive ability of enterosorbent powders and hydrogels prepared in acid and salt forms. Results of clinical trials conducted with the gel enterosorbents in the areas of gastroenterology and detoxication therapy are presented. In view of compatibility of carboxylated microcrystalline cellulose in hydrogel form with many biologically active ingredients, prospective character of using the enterosorbents not only as such but also as a matrix for the development of new dosage forms of other medications is pointed out. Examples showing advantages of such combinations in specific sustained release drug forms (ointments and microgranules) are given.     

Theoretical and Experimental Study of a Compact Planar Slow-Wave Structure on a Dielectric Substrate for the W-Band Traveling-Wave Tube

Technical Physics - A miniature planar meander-type slow-wave structure (SWS) for a W-band traveling-wave tube is studied. Computer simulation of the SWS electrodynamic parameters is performed. A...     

The effect of N2O4 on the crystalline structure of cellulose

Depending on reaction conditions, the system cellulose–N₂O₄ may give two different unstable crystalline compounds, one being an ester (cellulose trinitrite), the second, an adduct of cellulose and HNO₃ (the Knecht compound). For these compounds, mechanisms of the formation of the crystalline phase as a result of topochemical reaction and self-organization are discussed. The different characteristics of structural transformations of the fiber under nitrosation and nitration are noted. The existence of polymorphic forms of the Knecht compound is suggested. These labile nitrogen-containing compounds make possible the regeneration of cellulose in its various modifications (cellulose I, II, IV, or amorphous cellulose) from the cellulose–N₂O₄ system. The formation of unstable compounds and their ability to crystallize in the reaction medium allows the passage from amorphous cellulose to its crystalline modifications II or IV under mild conditions. The causes of decrystallization of cellulose by N₂O₄ are established. © 1993 John Wiley & Sons, Inc.     

Elastic and electrostatic properties of bamboo-shaped carbon nanotubes

A technology has been developed to synthesize films of bamboo-shaped carbon nanotubes from simple nanotubes by high-frequency oxygen plasma etching for 30 and 60 s. The electronic structure and mechanical properties of bamboo-shaped single-walled carbon nanotubes have been studied theoretically. Compartments in these structures are located at an optimum distance that corresponds to a decrease in the ionization potential and an improvement of the emission properties. It has been revealed that the Young’s and torsion moduli of the bamboo-shaped carbon nanotubes depend on the number of compartments. These tubes have their own dipole moments in contrast to the hollow defect-free tubes. It has been shown that bamboo-shaped nanotubes 1.37 nm in diameter are the most stable nanoclusters.