Order-disorder Transition (order-disorder + transition)

Distribution by Scientific Domains


Selected Abstracts


Order-disorder transitions in self-assembled polymers: A positron annihilation study

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
Ramasubbu Ramani
Abstract We report here the first results of order-disorder transition (ODT) in a self-assembled comb-like polymer-amphiphile supramolecular system as identified from the change in positron lifetime parameters. We have used poly(4-vinyl pyridine) hydrogen bonded with 3-pentadecyl phenol, which upon heating showed a stepwise reduction in o -Ps intensity at the ODT from lamellar self-assembled state to the disordered state. The ODT temperature was confirmed by differential scanning calorimetry and small angle X-ray scattering. The free volume "holes" in this polymer-amphiphile system are proposed to be near the chain ends of the polymer backbones. We suggest that positron lifetime spectroscopy can serve as a technique to identify ODTs in self-assembled lamellar structured supramolecular systems. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Synthesis, characterization and impedance spectroscopy of the new material [(CH3) (C6H5) 3P] 2CoBr4: a member of the A2BX4 family

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2008
M. F. Mostafa
Abstract The crystal structure of bis-(methyltriphenylphosphonium) tetrabromocobaltate (II), [(C19H18P)2 CoBr4] is determined: Mr = 933.203, monoclinic, P21, a = 9. 6977 (3) , b = 12.5547 (4), c = 16.4503 (6), , = 105.603 (2), V = 1929.04 (11)3, Z = 2, Dx = 1.607 Mg m -3, T = 298 K. Differential thermal analysis at high temperatures shows three endothermic peaks characterizing four phases, with onset temperatures at T1= 3132 K, T2 = 3204 K and T3= 3601 K. The structural instability detected via the temperature dependence of permittivity at T1 is ascribed to order-disorder transition associated with cation dipole reorientation. Permittivity and ac conductivity studies as a function of temperature (295 K-375 K) and frequency (0.11 kHz < f <100 kHz) are presented. The results indicate the importance of the cation size and shape on the phase transitions in the system. Bulk conductivity behavior is thermally activated. The associated activation energies are in the range 2.9 to 1.0 eV depending on the temperature regime. Two contributions to the ac conductivity, one dominating at low temperatures and high frequencies which are characterized by superlinear frequency exponent and the second dominates at high temperatures characterized by a sublinear frequency exponent. The behavior is interpreted in terms of the jump relaxation model. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Self-Assembly of Rod-Like Copolymers into Monolayers: A Simple Theoretical Estimate of Molecular Recognition Quality

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 7-8 2008
Anatoly V. Berezkin
Abstract A discrete model of a monolayer, consisting of identical rod-like copolymer molecules, is suggested. The influence of the copolymer's composition and sequence on its self-assembly was studied. Thermodynamic quantities of monolayers were calculated. It is shown that the system undergoes an "order-disorder" transition upon temperature increase. The most regular monolayers are formed by copolymers with quasi-random sequences. Nevertheless, the monomer composition of such "good" sequences can vary over a wide range. It is shown that homopolymers, copolymers with a predominance of one-type monomer units and copolymers consisting of a small number of large blocks have a reduced ability to self-assembly. [source]


Order-disorder transitions in self-assembled polymers: A positron annihilation study

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
Ramasubbu Ramani
Abstract We report here the first results of order-disorder transition (ODT) in a self-assembled comb-like polymer-amphiphile supramolecular system as identified from the change in positron lifetime parameters. We have used poly(4-vinyl pyridine) hydrogen bonded with 3-pentadecyl phenol, which upon heating showed a stepwise reduction in o -Ps intensity at the ODT from lamellar self-assembled state to the disordered state. The ODT temperature was confirmed by differential scanning calorimetry and small angle X-ray scattering. The free volume "holes" in this polymer-amphiphile system are proposed to be near the chain ends of the polymer backbones. We suggest that positron lifetime spectroscopy can serve as a technique to identify ODTs in self-assembled lamellar structured supramolecular systems. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Ordering Behavior of Layered Silicate Nanocomposites with a Cylindrical Triblock Copolymer

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2006
Chung Ho Lee
Abstract Summary: The ordering behavior of the nanocomposites of organically modified montmorillonite (OMMT) with a cylindrical triblock copolymer of polystyrene- block -poly(ethylene- co -butylene)- block -polystyrene (SEBS) has been investigated by temperature-resolved small-angle X-ray scattering (SAXS) and rheometry. X-Ray diffraction (XRD) confirms that the polymer chains are successfully intercalated with the interlayer gallery of the silicates. The data obtained from the SAXS and rheological measurements show that the addition of OMMT leads to a change in the microphase separation behavior of SEBS in the nanocomposites. The molecular interaction between OMMT and the polystyrene (PS) chains of SEBS decreases the structural perfection of the self-assembling, phase-separated domain structure of the nanocomposites. Rheological data exhibit that the order-order (TOOT) and order-disorder transitions (TODT) of the SEBS/OMMT nanocomposites decrease with the addition of OMMT. The highest elongation at break is obtained at approximately 2% OMMT and its further addition to the mixture leads to decreases in tensile strength and elongation. The change in the storage modulus (G,) of a) SEBS, b) S98M2, c) S95M5, and d) S90M10, as a function of temperature in the range of 150,,,T (C),,,260. [source]