High proton conductivity in a flexible, cross-linked, ultramicroporous magnesium tetraphosphonate hybrid framework

Multifunctional materials, especially those combining two or more properties of interest, are attracting immense attention due to their potential applications. MOFs, metal organic frameworks, can be regarded as multifunctional materials if they show another useful property in addition to the adsorption behavior. Here, we report a new multifunctional light hybrid, MgH(6)ODTMP·2H(2)O(DMF)(0.5) (1), which has been synthesized using the tetraphosphonic acid H(8)ODTMP, octamethylenediamine-N,N,N',N'-tetrakis(methylenephosphonic acid), by high-throughput methodology. Its crystal structure, solved by Patterson-function direct methods from synchrotron powder X-ray diffraction, was characterized by a 3D pillared open framework containing cross-linked 1D channels filled with water and DMF. Upon H(2)O and DMF removal and subsequent rehydration, MgH(6)ODTMP·2H(2)O (2) and MgH(6)ODTMP·6H(2)O (3) can be formed. These processes take place through crystalline-quasi-amorphous-crystalline transformations, during which the integrity of the framework is maintained. A water adsorption study, at constant temperature, showed that this magnesium tetraphosphonate hybrid reversibly equilibrates its lattice water content as a function of the water partial pressure. Combination of the structural study and gas adsorption characterization (N(2), CO(2), and CH(4)) indicates an ultramicroporous framework. High-pressure CO(2) adsorption data are also reported. Finally, impedance data indicates that 3 has high proton conductivity σ = 1.6 × 10(-3) S cm(-1) at T = 292 K at ~100% relative humidity with an activation energy of 0.31 eV.     

Efficient Solution Concepts and Their Relations in Stochastic Multiobjective Programming

In this work, different concepts of efficient solutions to problems of stochastic multiple-objective programming are analyzed. We center our interest on problems in which some of the objective functions depend on random parameters. The existence of different concepts of efficiency for one single stochastic problem, such as expected-value efficiency, minimum-risk efficiency, etc., raises the question of their quality. Starting from this idea, we establish some relationships between the different concepts. Our study enables us to determine what type of efficient solutions are obtained by each of these concepts.     

The effect of aryl nitration on gas sorption and permeation in polysulfone

CO_2, CH_4, O_2, and N₂ permeability and solubility of unmodified and aryl-nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N_2, O_2, and CH₄ do not show a systematic dependence on degree of substitution. However, CO₂ solubility apparently goes through a minimum as the degree of substitution is increased. CO₂ solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO₂/CH₄ solubility selectivity increases monotonically as the degree of substitution increases. CO₂/CH₄ permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc.     

Texture dependence of capillary instabilities in nematic liquid crystalline fibres

Static and dynamic linear analyses of axisymmetric capillary instabilities in textured nematic liquid crystalline fibres are performed using the equations of nemato-statics and inviscid nemato-dynamics. Three representative textures, viz. axial, onion, and radial, are analysed to show all possible effects of Frank gradient elasticity on the wavelength selection and growth rate of peristaltic modes driven by surface area reduction. It is found that Frank elasticity may tend to stabilize or destabilize the fibre, depending on the initial fibre texture. Axial textures tend to stabilize the fibre through the director splay-bend distortions driven by surface tilting. Onion textures are destabilized by decreasing azimuthal bend elastic energy caused by surface displacement. Radial textures exhibit a stabilizing tilt mechanism due to bend modes and a destabilizing displacement mechanism due to splay modes, but the former is predicted to be dominant. The static analysis provides good estimates of the instability thresholds while the transient energy balance provides information on the fastest growing modes. The static and dynamic results are compared and shown to be fully consistent. The couplings between splay and/or bend distortions, surface tilting, and surface displacement in nematic fibres are characterized and used to explain the deviations from the classical Rayleigh instability.     

Thermodynamics of soft anisotropic contact lines

Contact lines arising from the intersection of interfaces between liquids and nematic liquid crystals are representative models of soft anisotropic contact lines. This paper presents the thermodynamics of soft anisotropic contact lines and the derivation of the one dimensional (1D) Gibbs-Duhem adsorption equation. Consistency between the 1D Gibbs-Duhem equation and the classical equations of lineal nematostatics is shown. Using a phase space that takes into account thermodynamics, liquid crystalline order, and geometric variables, the generalized nematic line Gibbs-Duhem equation reveals the presence of couplings between curvature, torsion, adsorption, temperature, and average molecular orientation. Merging the thermodynamic analysis with nematostatics results in a model for contact line shape and orientation selection. The ability of an adsorbed solute to orient the director and to bend and twist the contact line is predicted. The thermodynamic origin of preferred orientation at a straight contact line is established.     

Surface behavior of oleoyl palmitoyl phosphatidyl ethanolamine (OPPE) and the characteristics of mixed OPPE-miltefosine monolayers

Langmuir monolayers of oleoyl palmitoyl phosphatidyl ethanolamine (OPPE) were investigated at the air/water interface by means of surface pressure (pi)-area (A) isotherms complemented with Brewster angle microscopy images upon film compression/expansion. The characteristic phase transition appearing in the course of pi/A isotherms was attributed to the coexistence of two liquid-expanded phases of different molecular ordering. The interactions between OPPE and hexadecylphosphocholine (miltefosine) were studied at different subphase pHs (2, 6, and 10) at 20 degrees C and analyzed with mean molecular area (A12)-, excess area of mixing (Aexc)-, and excess free energy of mixing (DeltaGexc)-composition plots. The obtained results indicate that at pH 10, where both OPPE and miltefosine polar groups are negatively charged, attractive interactions are observed (reflected by negative deviations from ideality), contrary to expectation. This peculiar behavior is explained as being due both to water molecules, which surround negatively charged polar groups and increase the distance between them, weakening in this way the electrostatic repulsion forces; and to positively charged counterions present in the diffuse double layer, neutralizing their charge. In this way, the van der Waals attraction forces between hydrocarbon tails of both molecules predominate and are responsible for the observed negative deviations from ideal behavior. Similar explanations are given for the observed negative deviations at pH 2 where both polar groups are positively charged. At pH 6, the observed negative deviations at low surface pressures and positive deviations at high pressures are interpreted as being due to a change in orientation of polar groups upon monolayer compression.     

1,1-Dihalogenoanthra [b]cyclopropenes. Preliminary communication

1,1-Dichloro- and 1,1-difluoroanthra [b]cyclopropene ( 1 and 2 ) are synthesized in 8 steps from the Diels-Alder adduct of benzocyclobutene and maleic anhydride.