A brief discussion: Thermodynamic and dynamic fragilities,non-divergent dynamics and the Prigogine–Defay ratio

This article brings together some of the work performed by the present author and collaborators that is related to the glass transition event and to some of its entropy aspects. The purpose of the work and discussion was motivated by a view that some of the frameworks in which we currently look at glassy behavior, while potentially useful, may also have limitations that we often do not fully consider. Discussion focuses on isochoric glass formation paths, thermodynamic and dynamic fragilities and how dynamic fragility in many systems (especially polymers, metals, ionic liquids and hydrogen bonding systems) seems to vary primarily with the glass transition temperature itself. This leads to the conclusion that such systems have an apparent activation energy that varies as the square of the glass temperature. The work then discusses evidence for a non-diverging relaxation time or viscosity as the glass temperature is approached and ends with a discussion of the Prigogine–Defay ratio.     

Thermotropic Liquid-Crystalline Polymers,Re-Entrant and Discotic Liquid Crystals. A Bibliography for 1977–1984

This bibliography contains bibliographic data of books and papers concerning the thermotropic liquid-crystalline polymers, re-entrant and discotic liquid crystals for 1977–1984 years. The bibliography of the thermotropic liquid-crystalline polymers contains also bibliographic data of papers describing both the thermotropic and lyotrophic behavior of the liquid-crystalline polymers, liquid-crystalline melts, solutions of thermotropic liquid-crystalline polymers, solutions of polymer chains in a nematic solvent and some polymerization problems. In this bibliography are included also bibliographic data of papers which according to the citation in the literature are important for the study of both the thermotropic and lyotropic liquid-crystalline polymers. In the bibliography of the re-entrant liquid crystals (at atmospheric pressure) are included the papers published after the first work in this field of Cladis (Phys. Rev. Lett. 35, 48–51 (1975)) up to the end of 1984 year. Similarly, in the bibliography of the discotic liquid crystals are included the papers published after the first work of Chandrasekhar, Sadashiva and Suresh (Pramana 9, 477–480, (1977)) also up to the end of 1984 year.     

Crystallization of amorphous silicates far from equilibrium part I: A versatile nitrate-based sol–gel synthesis of amorphous porous Ca,Mg-rich silicates

An easy-to-use, comprehensive sol–gel method is developed to produce amorphous calcium and magnesium silicates from nitrate precursors and TetraEthOxySilane (TEOS). Final products were designed to suit basic prerequisites of starting materials for experimental investigation of crystallization around the glass transition temperature range. After gelification, thermo-gravimetric methods and infrared-spectroscopy were used to follow dehydration, decarbonation and denitrification of the xerogel. A temperature of 500 °C is found to successfully remove volatiles without causing crystallization. The microstructure revealed by transmission electron microscopy (TEM) consists of 10–20 nm individual mesoparticles of 10–20 nm. Samples annealed at 500 °C were found entirely amorphous at the TEM scale. The porosity observed by TEM and characterized by nitrogen adsorption–desorption is homogeneous and varies from 4.6 to 8.5 nm as a function of the composition. Bulk analyses by ICPMS and local analyses by EDS-TEM demonstrate that the stoichiometry can be achieved and the homogeneity is confirmed at least down to 100 × 100 nm. At lower scale, irradiation by the electron beam produces a significant volatilization of Ca and Mg, which makes chemical analyses unreliable. Pros and cons of the method and special cares for specific applications are discussed. The method was also successfully used to produce a wider range of amorphous analogs having complex compositions or containing trace elements for applications in the field of mineral physics and chemistry.     

A metastable liquid state miscibility gap in undercooled Pd–Ni–P melts

Recently, phase separation was found to occur in Pd_41.25Ni_41.25P_17.5 bulk metallic glasses (BMG), which have a negative heat of mixing among the constituent elements. In this work, Pd_40 + 0.5xNi_40 + 0.5xP_20 ? x BMG with x = 0 to 3.5, were studied for amorphous phase separation. It occurs for x ? 1, but absent for x ? 1. In addition, in phase-separated specimens, the characteristic sizes or wavelengths of the decomposed phases were measured. It was found that they obey the lever rule. The experimental results suggest the existence of a metastable liquid/amorphous miscibility gap. Its origin is attributed to unique short range orders in the undercooled Pd–Ni–P melts.     

A Novel Co(II) Metal–Organic Framework Based on 6-Methylpyridine-2,4-dicarboxylic Acid N-oxide: Synthesis,Crystal Structure and Thermal Stability

Abstract  

A novel metal–organic framework based on 6-methylpyridine-2,4-dicarboxylic acid N-oxide (MPDCO) ligand, [Co(MPDCO)(bix)_0.5(H₂O)₂] _n (bix = 1,4-bis(imidazol-1-ylmethyl)-benzene), has been prepared and structurally characterized. Single crystal X-ray analysis shows that it crystallizes in the monoclinic space group of P2₁/n with four independent lattice parameters a = 10.269(2) ?, b = 10.462(2) ?, c = 15.875(4) ?, and β = 107.657(4)°, and it has four independent molecules in the unit cell (Z = 4). A one-dimensional (1-D) helical chain was formed through the MPDCO spacer and Co²⁺ centers along the a-axis. Then, these 1-D chains were further interconnected by the bidentate ligand bix to afford an infinite puckered 2-D herringbone framework with (6,3) topology. And a 3-D supramolecular network was formed through the strong intermolecular hydrogen bonds.