Effect of solvent media and condensed benzene rings on thermochemical behaviour of dibenzo-18-crown-6 in solution

The specific and non-specific interactions of twelve activated carbon cloth samples prepared from commercial cotton fabric, and that present different activation degrees are studied through the determination of immersion enthalpies in CCl₄ and H₂O, and in aqueous solutions of NaOH and HCl. The immersion enthalpies found for the solvents CCl₄ and H₂O are in a range of 5.49–45.84 and 1.77–7.76 J g⁻¹, respectively. The enthalpic values for the materials in aqueous solutions of NaOH and HCl, allow characterizing the chemical surface of these materials, which are in a range of 6.63 and 21.49 J g⁻¹, finding through them important relations in company with other characterizing techniques used in the study of these materials.     

Phase transformation kinetics induced in thin sol-gel PZT films under thermal annealing

The surface morphology evolution and phase transformation kinetics in thin lead zirconate-titanate (PZT) sol-gel films during rapid thermal annealing were studied by in situ measurement of scattered light intensity and by recording successive instantaneous optical microscope images. We also studied the variation of the texture perfection, the fraction of the growing phase, and the angular dependence of the scattered intensity in partially annealed samples. The parameters characterizing the kinetics of the pyrochlore-perovskite phase transformation were derived by a mathematical treatment of the experimental data. The phase transformation kinetics and the film crystalline texture are shown to depend substantially on the pyrolysis temperature. The texture formation mechanism is considered.     

Structural features and thermal stability of molecular complexes of 25,26,27,28-Tetrahydroxycalix[4]arene with solvents

A single crystal of the complex 25,26,27,28-tetrahydroxycalix[4]arene with hexane is grown via slow evaporation of a solution, and its full structure is determined. A molecular complex of 25,26,27,28-tetrahydroxycalix[4]arene with toluene is prepared for the first time, and its thermal stability is studied. The kinetic curves of the sorption of saturated vapors of acetone, acetonitrile, n-hexane, and toluene on 25,26,27,28-tetrahydroxycalix[4]arene are experimentally obtained. It is shown that the sorption of acetonitrile vapors on 25,26,27,28-tetrahydroxycalix[4]arene is characterized by a pronounced maximum corresponding to a stoichiometry of 1: 1. It is assumed that the structural reorganization of 25,26,27,28-tetrahydroxycalix[4]arene results in the transport of acetonitrile molecules within the molecular crystal, followed by complexation to form a thermodynamically stable hexagonal structure. The high thermal stability of solvates of 25,26,27,28-tetrahydroxycalix[4]arene is found to be due to the strict proportionality of the form and size of a guest molecule to those of the cavity of a host molecule.     

On the space of real polynomials without multiple critical values

Moscow State University. Translated from Funktsional'nyi Analiz i Ego Prilozheniya, Vol. 26, No. 2, pp. 10–17, April–June, 1992.