Capillary bridging and long-range attractive forces in a mean-field approach

When a mixture is confined, one of the phases can condense out. This condensate, which is otherwise metastable in the bulk, is stabilized by the presence of surfaces. In a sphere-plane geometry, routinely used in atomic force microscope and surface force apparatus, it can form a bridge connecting the surfaces. The pressure drop in the bridge gives rise to additional long-range attractive forces between them. By minimizing the free energy of a binary mixture we obtain the force-distance curves as well as the structural phase diagram of the configuration with the bridge. Numerical results predict a discontinuous transition between the states with and without the bridge and linear force-distance curves with hysteresis. We also show that similar phenomenon can be observed in a number of different systems, e.g., liquid crystals and polymer mixtures.     

Rate of approximation by rectangular partial sums of double orthogonal series

( ) . .

---

---

Dedicated to Professor K. Tandori on his seventieth birthday

---

This research was supported in part by Grant # K41 100 of the Joint Fund of the Government of Ukraine and the International Science Foundation.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.     

Synthesis and crystal structure of new coordination polymers based on sodium aqua complexes and macrocyclic cavitand cucurbit[6]uril

The crystals of the compounds [Na₄(H₂O)₁₄CB[6]](bdc)₂ · 13H₂O (1) and [Na₆(H₂O)₁₉CB[6]]-(bdc)₃ ·15H₂O (2) were obtained by heating an aqueous solution of sodium terephthalate (Na₂bdc) and cucurbit[6]uril (CB[6]). According to the single-crystal X-ray diffraction data, the sodium aqua complexes and cucurbit[6]uril molecules form chains (in structure 1) and layered metal-organic frameworks (in structure 2). The structures of the sodium aqua complexes [Na₃(H₂O)₁₀]³⁺ in 1 and [Na₆(H₂O)₁₉]³⁺ in 2 have been previously unknown. When submitted to ultraviolet radiation, crystals of 1 and 2 exhibit luminescence with an emission maximum at 428 and 434 nm, respectively.

     

Molecular simulation and theory of a liquid crystalline disclination core

Molecular simulations of a nematic liquid crystal confined in cylinder geometry with homeotropic anchoring have been carried out. The core structure of a disclination line defect of strength +1 has been examined, and comparison made with various theoretical treatments, which are presented in a unified way. It is found that excellent fits to the cylindrically symmetrized order tensor profiles may be obtained with appropriate parameter choices; notwithstanding this, on the time scales of the simulation, the cylindrical symmetry of the core is broken and two defects of strength +1 / 2 may be resolved.     

Electronic structure and photoelectron spectra of scandium and lutecium acetylacetonates and acetylacetoniminates

Scientific-Research Physicotechnical Institute, Far-East State University. M. V. Lomonosov Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 4, pp. 51–55, July–August, 1990.     

Charge transport in columnar mesophases of carbazole macrocycles

Charge transport properties of a columnar mesophase of carbazole macrocycles are analyzed. Realistic morphologies are sampled using all-atom molecular dynamics simulations while charge transport is simulated using the kinetic Monte Carlo method with transfer rates obtained from the high temperature nonadiabatic limit of Marcus theory. It is shown that the molecular design with side chains pointing inside the macrocycle allows close approach between molecules of neighboring columns, thus enabling three-dimensional transport and helping to circumvent charge trapping on structural defects.     

On the almost-everywhere convergence of the Riesz means of double orthogonal series

We establish coefficient conditions of the classical type that guarantee the almost-everywhere summability of double orthogonal series by the Riesz methods of nonnegative order. We also prove certain equiconvergence theorems. South-Ukrainian Pedagogic University, Odessa. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 51, No. 7, pp. 867–880, July, 1999.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the thermal decomposition of dinitramide in aqueous solutions of HNO₃, in anhydrous acetic acid, and in several other organic solvents were studied. The rate of the decomposition of dinitramide in aqueous HNO₃ is determined by the decomposition of mixed anhydride of dinitramide and nitric acid (N₄O₆) formed in the solution in the reversible reaction. The decomposition of the anhydride is a reason for an increase in the decomposition rates of dinitramide in solutions of HNO₃ as compared to those in solutions in H₂SO₄ and the self-acceleration of the process in concentrated aqueous solutions of dinitramide. The increase in the decomposition rate of nondissociated dinitramide compared to the decomposition rate of the N(NO₂)₂ ⁻ anion is explained by a decrease in the order of the N−NO₂ bond. The increase in the rate constant of the decomposition of the protonated form of dinitramide compared to the corresponding value for neutral molecules is due to the dehydration mechanism of the reaction. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 41–47, January, 1998.