Search results for "Phase"
showing 10 items of 6344 documents
Pressure effect studies on spin crossover systems
2005
Abstract In the present review article we discuss the results of investigations of the influence of hydrostatic pressure (up to 1.2 GPa) on the spin transition behaviour in coordination compounds of 3d transition metal ions. The systems under investigation are mononuclear spin crossover compounds of iron(II) and chromium(II), dinuclear complexes of iron(II) exhibiting coexistence of intramolecular anti-ferromagnetic coupling and thermal spin crossover, and 1D, 2D and 3D polynuclear spin crossover complexes of iron(II). It is demonstrated that the application of hydrostatic pressure serves as a tool for modifying the ligand field strength in a controlled manner.
Phase transitions and distortion of [BiCl6]3- octahedra in (C3H5NH3)3[BiCl 6] - DSC and single-crystal X-ray diffraction studies
2004
The DSC diagram of tris(allylammonium) hexachlorobismuthate(III), (C3H5NH3)3[BiCl6], revealed three anomalies at 152, 191 and 299 K. The structure of the salt was determined at 200 and 315 K, below and above the high-temperature phase transition at 299 K. In both phases the crystals are monoclinic. At 200 K the space group is C2/c whereas at 315 K it is C2/m. The structures, at both temperatures, are composed of [BiCl6]3− octahedra and allylammonium cations. The organic and inorganic moieties are attracted to each other by a network of the N-H. . .Cl hydrogen bonds. The relationship between corresponding parameters of the unit cells has been found. The phase transition at 299 K, of the orde…
New conducting radical salts based upon Keggin-type polyoxometalates and perylene
2004
Three new radical salts, Per6[PMo12O40]·CH2Cl2 (1), Per6[PMo12O40]·CH3CN (2), and Per9(NBu4)4[SiW12O40]2 (3) (Per = perylene), have been synthesised and their electrical and magnetic properties characterised. These three salts are diamagnetic and they behave as semiconductors with room temperature conductivities of 69, 3.6 and 0.85 S cm−1. While salt 2 presents hole-type conduction and 3 exhibits electron-dominated electrical transport properties, salt 1 shows at 150 K an abrupt change in the thermal dependence of the electrical conductivity and the Seebeck coefficient suggesting a phase transition.
Temperature triggered self-assembly of polypeptides into multivalent spherical micelles.
2007
We report herein thermally responsive elastin-like polypeptides (ELPs) in a linear AB diblock architecture with an N-terminal peptide ligand that self-assemble into spherical micelles when heated slightly above body temperature. A series of 10 ELP block copolymers (ELP(BC)'s ) with different molecular weights and hydrophilic-to-hydrophobic block ratios were genetically synthesized by recursive directional ligation. The self-assembly of these polymers from unimers into micelles was investigated by light scattering, fluorescence spectroscopy, and cryo-TEM. These ELP(BC)'s undergo two phase transitions as a function of solution temperature: a unimer-to-spherical micelle transition at an interm…
Phases and phase transitions of (NaCl)1?x(NaCN)x
1985
(NaCl)1−x(NaCN)x mixed crystals with CN-concentrationsx of 0.87, 0.76, 0.71 and 0.65 have been investigated by X-ray powder diffraction. Apart from the cubic room temperature phase, a rhombohedral and an orthorhombic phase have been identified. In addition a glass state has been observed which is characterized by a strong broadening of the cubic powder lines. The phase diagram shows a wide coexistence gap between the non-cubic phases and the glass state.
Orientational ordering transitions of semiflexible polymers in thin films: A Monte Carlo simulation
2011
Athermal solutions (from dilute to concentrated) of semiflexible macromolecules confined in a film of thickness D between two hard walls are studied by means of grand-canonical lattice Monte Carlo simulation using the bond fluctuation model. This system exhibits two phase transitions as a function of the thickness of the film and polymer volume fraction. One of them is the bulk isotropic-nematic first-order transition, which ends in a critical point on decreasing the film thickness. The chemical potential at this transition decreases with decreasing film thickness ("capillary nematization"). The other transition is a continuous (or very weakly first-order) transition in the layers adjacent …
Preparation of actuating fibres of oriented main-chain liquid crystalline elastomers by a wetspinning process
2011
We present a versatile method to prepare oriented fibres with a defined thickness from main-chain liquid crystalline elastomers. A microfluidic setup is utilized to inject a solution of a photocrosslinkable smectic A main-chain polymer into a co-flowing stream of silicone oil. Diffusion of the solvent into the oil yields solid polymer filaments that are crosslinked in a continuous way by UV-irradiation. The obtained fibres are highly oriented and show a reversible and significant contraction during the liquid crystal's phase transition.
Phases and phase transitions in the mixed molecular system (NaCN)1x(KCN)x
1990
The phase diagram of (NaCN)1−x(KCN)x was examined by neutron powder diffraction in the temperature range 5K ≦T≦300 K. Several non-cubic low-temperature phases were identified for concentrationsx<xc1=0.15 andx≧xc2=0.89. Lattice parameters and ferroelastic deformations were determined from the observed powder patterns. The phase transformations were characterized following the temperature dependence of the appropriate order parameters.
I. Glass Transition. Theoretical concepts on the glass transition of polymers and their test by computer simulation
1996
Various organic molecules, in particular polymers, are extremely good glass formers and allow the study of supercooled melts near the glass transition in metastable equilibrium. Theories of the glass transition imply such an equilibrium (e.g. mode-coupling theory, or Gibbs-di Marzio theory) and can hence be tested in these systems. Simplified lattice models for polymer melts (e.g. the bond fluctuation model) have been developed that can very efficiently be studied by Monte-Carlo simulation, and although they fail to accurately describe the local structure, they describe many features of the experiments very well. In this model, the mechanism of the glass transition is a competition between …
Self-organization of substituted azacrowns based on their discoid and amphiphilic nature
1989
Abstract Cyclame and hexacyclene derivatives, bearing four and six long-chain substituents respectively, were synthesized. They are discussed as monolayer-forming amphiphiles as well as liquid-crystalline-phase-forming thermotropic mesogens. The compounds investigated form ordered monolayers at the gas/water interface. In the monolayer the hydrophilic cyclic head group lies flat on the water surface, whereas the hydrophobic substituents are oriented perpendicularly with respect to the interface. Most derivatives fitted with aromatic substituents exhibit a solid condensed state exclusively. In contrast with this, solid condensed as well as expanded phases can be found when spreading the alip…