Home About us Contact
|
Home About us Contact | ||
|
|
||
Phase-transition Temperature (phase-transition + temperature)
Selected AbstractsPhase-Transition Temperatures of Strained Single-Crystal SrRuO3 Thin FilmsADVANCED MATERIALS, Issue 6 2010Kyoung Jin Choi The temperature dependence of in-plane and out-of-plane lattice parameters of a compressively strained SrRuO3 thin film grown on a SrTiO3 substrate is reported. The structural transition temperature of the SrRuO3 thin film shifts by more than 200,°C toward the lower-temperature region due to compressive strain (see graph). [source] Synthesis and Characterization of Pyrazolyl-Functionalized Imidazolium-Based Ionic Liquids and Hemilabile (Carbene)palladium(II) Complex Catalyzed Heck ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2007Ruihu Wang Abstract Neat reactions of 1-(pyrazolylmethyl)imidazole with an excess of alkyl or polyfluoroalkyl halides at 100 °C followed by subsequent metathetical reactions with LiN(SO2CF3)2 or KPF6 at 25 °C gave rise to a series of monoquaternary salts 3a,3k. These salts can be also prepared through treatment of 1-alkylimidazole with 1-(chloromethyl)pyrazole hydrochloride in the presence of base, followed by anion exchange with LiN(SO2CF3)2 or KPF6. Their phase-transition temperature, thermal stability, density and solubility in common solvents have been investigated. Most of the bis(trifluoromethanesulfon)amide salts are room-temperature ionic liquids. The effect of anions and of alkyl substituents bonded to the imidazolium cation on the physicochemical properties was examined. Using 3-butyl-1-(pyrazolylmethyl)imidazolium chloride (2d), the precursor of 3-butyl-1-(pyrazolylmethyl)imidazolium bis(trifluoromethanesulfon)amide (3d), as a reactant, a hemilabile (N-heterocyclic carbene)palladium(II) complex 4 was synthesized through a (carbene)silver(I) transfer reagent. It was characterized by single-crystal X-ray diffraction analysis. The catalytic activity and recyclability of 4 in 3d were preliminarily evaluated by consecutive Heck reactions using different substrates. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Novel side-chain liquid-crystalline polyimide for film materialsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2003Haojun Fan Abstract A novel side-chain liquid-crystalline polyimide (SLCPI) was prepared via copolycondensation from 3,5-diamino-benzonic-4,-biphenyl ester, 4,4,-diamino- biphenyl ether, and 3,3,,4,4,-oxydiphthalic dianhydride. The energy-minimized structure and liquid crystallinity of SLCPI were investigated by molecular modeling, differential scanning calorimetry (DSC), wide-angle X-ray scattering, and polarized optical microscopy, respectively. The results indicated that this polyimide (PI) with side-chain mesogenic units exhibited a nematic NI phase. Because of the in situ self-reinforcement of side-chain mesogenic units, the improved tensile strength and modulus of PI films reached 270% and 300%, respectively. The coefficient of thermal expansion of films decreased by 40%. DSC and thermogravimetric analyses indicated that the phase-transition temperature of SLCPI was above 240 °C, and the 5% weight-loss temperature was above 520 °C. Moreover, copolycondensation of two diamines with dianhydride and incorporation of pendent mesogenic units diminished the regularity and symmetry of main chains; as a result, SLCPI exhibits good film processability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 554,559, 2003 [source] Salt-Induced Depression of Lower Critical Solution Temperature in a Surface-Grafted Neutral Thermoresponsive PolymerMACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2006Young K. Jhon Abstract Summary: Quartz crystal microbalance with dissipation monitoring (QCM-D) is employed to determine the effect of salt on the volume phase transition of thermoresponsive polymer brushes. Changes in mass and viscoelasticity of poly(N -isopropylacrylamide) (PNIPAM) layers grafted from a QCM-D crystal are measured as a function of temperature, upon contact with aqueous solutions of varying salt concentrations. The phase-transition temperature of PNIPAM brushes, TC,graft, quantified from the QCM-D measurements is found to decrease as the concentration of salt is increased. This phenomenon is explained by the tendency of salt ions to affect the structure of water molecules (Hofmeister effect). However, in contrast to the linear decrease in phase-transition temperature upon increasing salt concentration observed for free PNIPAM, the trend in TC,graft for PNIPAM brushes is distinctively non-linear. Schematic representation of the effect of salt concentration on the phase transition behavior of thermoresponsive polymer brushes. [source] Thermal hysteresis of the phase-transition temperature of single-crystal GdB6PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006M. Reiffers Abstract The phase transition of a single-crystal sample of GdB6, oriented along the ,111, axis using the temperature dependence of electrical resistivity , (T ), susceptibility , (T ) and heat capacity C (T ) under an applied magnetic field was studied. , (T ) has shown 2 anomalies , a sharp drop at TN1 = 15.4 K and a small maximum at TN2 = 9.1 K with thermal hysteresis effect. , (T ) shows the anomalies at both transition temperatures. C (T ) shows similar thermal hysteresis effect at TN2. The small maximum at TN2 decreases its position to lower temperatures with increasing magnetic field. The peak at TN1 is practically unaffected by an applied magnetic field up to 9 T. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of annealing temperature on the crystalline quality and phase transformation of Chemically Deposited CdSe filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2005M. Zapata-Torres Abstract Polycrystalline CdSe thin films were grown on glass substrates by chemical bath deposition at 50 ºC. The samples were annealed in air atmosphere at different temperatures and characterized by X-ray diffraction and Raman spectroscopy. It was found that the as-grown films have cubic structure. These samples maintain their cubic structure for annealing temperatures between 60 ºC and 300 ºC. For annealing temperatures higher than 300 ºC we obtain a mixture of cubic and hexagonal phases. The analysis made by X-ray diffraction and Raman dispersion show that the samples annealed at temperatures under the phase-transition temperature increase their crystalline quality. In order to determinate the temperature for the complete transition of the cubic phase, we used the precipitated material obtained during the grown of the CdSe films. This material was annealed on air atmosphere between 300 °C and 500 °C with 50 ° intervals. The samples were measured by X-ray diffraction. The samples maintained the cubic structure if the annealing temperature is under 300 °C. For temperatures between 300 °C and 450 °C we found a mixture of cubic and hexagonal phase. For an annealing temperature of 500°C we obtain only the hexagonal phase. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Incommensurate structure of Ca2Al2O5 at high temperatures , structure investigation and Raman spectroscopyACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2008Biljana Lazic A high-temperature X-ray diffraction study revealed that brownmillerite-type Ca2Al2O5 transforms to an incommensurately modulated structure at elevated temperatures. Single crystals of Ca2Al2O5 were synthesized in an end-loaded piston cylinder press at 2.5,GPa and 1273,K. The diffraction pattern observed at 1090,(10),K by in situ single-crystal diffraction experiments can be indexed by an I -centred orthorhombic cell and a modulation wavevector of q = 0.595,(1)c*. A (3,+,1)-dimensional model in superspace group Imma(00,)s00 was used to refine the modulated structure. The structure is assembled from two building units: (i) layers of corner-sharing [AlO6] octahedra, stacked along b alternate with (ii) layers of zweier single chains of [AlO4] tetrahedra running along a. The modulated structure arises from an aperiodic sequence of two different configurations of the chains within the tetrahedral layers. The modulated high-temperature phase of Ca2Al2O5 is isotypic to the modulated high-temperature modification of Ca2Fe2O5. A large hysteresis was found in the phase-transition temperature. On heating, the transition occurs at ca 1075,(10),K; on cooling, satellite reflections can be observed down to 975,(10),K. The characterization of Ca2Al2O5 is completed by Raman spectroscopy, including a partial interpretation of the spectra. [source] Thermo-Switchable Charge Transport and Electrocatalysis Using Metal-Ion-Modified pNIPAM-Functionalized ElectrodesADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Michael Riskin Abstract Metal ions (Ag+, Cu2+, Hg2+) are incorporated into an electropolymerized, poly(N -isopropyl acrylamide), pNIPAM, thermosensitive polymer associated with an electrode using the "breathing-in" method. The ion-functionalized pNIPAM matrices reveal ion-dependent gel-to-solid phase-transition temperatures (28,±,1,°C, 25,±,1,°C, 40,±,1,°C for the Ag+, Cu2+, and Hg2+ -modified pNIPAM, respectively). Furthermore, the ion-functionalized polymers exhibit quasi-reversible redox properties, and the ions are reduced to the respective Ag0, Cu0, and Hg0 nanocluster-modified polymers. The metal-nanocluster-functionalized pNIPAM matrices enhance the electron transfer (they exhibit lower electron-transfer resistances) in the compacted states. The electron-transfer resistances of the metal-nanocluster-modified pNIPAM can be cycled between low and high values by temperature-induced switching of the polymer between its contracted solid and expanded gel states, respectively. The enhanced electron-transfer properties of the metal nanocluster-functionalized polymer are attributed to the contacting of the metal nanoclusters in the contracted state of the polymers. This temperature-switchable electron transfer across a Ag0 -modified pNIPAM was implemented to design a thermo-switchable electrocatalytic process (the temperature-switchable electrocatalyzed reduction of H2O2 by Ag0 -pNIPAM). [source] Photoresponsive Ferroelectric Liquid-Crystalline PolymersADVANCED FUNCTIONAL MATERIALS, Issue 1 2007P. Beyer Abstract The photoresponse of ferroelectric smectic side-chain liquid-crystalline (LC) polymers containing a photoisomerizable azobenzene derivative as a covalently linked photochromic side group is investigated. By static measurements in different photostationary states, the effect of trans,cis isomerization on the material's phase-transition temperatures and its ferroelectric properties (spontaneous electric polarization PS and director tilt angle ,) are analyzed. It turns out that the Curie temperature (transition SC* to SA) can be reversibly shifted by up to 17,°C. The molecular mechanism of this "photoferroelectric effect" is studied in detail using time-resolved measurements of the dye's optical absorbance, the director tilt angle, and the spontaneous polarization, which show a direct response of the ferroelectric parameters to the molecular isomerization. The kinetics of the thermal reisomerization of the azo dye in the LC matrix are evaluated. A comparison to the reisomerization reaction in isotropic solution (toluene) reveals a faster thermal relaxation of the dye in the LC phase. [source] | ||||||||||||||||||||||||||||