Quantum dynamics of relaxation of a pair of coupled Morse oscillators: Effects of mass and electrical asymmetries

A multiconfiguration time‐dependent Hartree method based recipe is used to study the role of mass and electrical asymmetry in controlling the quantum dynamics of relaxation of a locally excited O? H bond in a water molecule, modeled by a pair of interacting Morse oscillators. The fast periodic energy transfer between the two equivalent O? H bonds in H? O? H is replaced by a rather slow process when one of the H atom is replaced by a deuterium atom. Application of static electric field along the O? D bond in HOD molecule is seen to either enhance or damp the relaxation rate, depending on the strength of the applied field. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Effect of Supermolecular Structure Changes on the Glass Transition of Polymer

The idea of two miscellaneous amorphous fractions in one polymeric system is under consideration. A new factor influencing the glass transition and a relaxation observed in polymers exhibiting different supermolecular structures is discussed. In order to clarify the specific arrangement of backbone chains two types of polymers were taken under investigation: semicrystalline poly(4-methyl-1-pentene) and a liquid-crystalline poly(norbornene) derivative. In both cases,it was possible to find two well separated glass transitions. Differential scanning calorimetry and dynamic mechanical thermal analysis were used to study the effect of thermal history on the assignment of the glass transition event associated with two miscellaneous amorphous phases. The problem of molecular arrangement in the amorphous phases is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Energy and capacity time correlation functions for investigation of vibrational energy relaxation

Vibrational energy relaxation of a diatomic solute in a liquid solvent is investigated by means of the generalized Langevin equation. The vibrational energy, velocity and capacity time correlation functions (TCFs) are considered. It is shown that the detailed structure of the energy TCF contains an initial fast (subpicosecond) decay segment that is followed by weak oscillations on the background of an exponential relaxation curve. The direct method for evaluating the relaxation rate constant from equilibrium molecular dynamics simulations of a flexible solute is proposed and implemented. The closed form expressions for the memory function and for the relaxation rate constant in terms of quantities accessible from the simulations are derived. The simulation results for rigid and flexible solutes are compared and analyzed.     

Ion association and ultrasonic relaxation in hydrogen-bonding solvents: 1:1 Electrolytes in 2-propanol at 25°C

Ultrasonic absorption measurements have been carried out in aqueous solutions of Bu₄NCl, Bu₄NBr, Bu₄NI, Me₄NCl, and LiCl in 2-propanol over the frequency range 15–250 MHz. A single relaxation frequency was observed for each system. All the data were found to be consistent with a 2-step association mechanism in which the rate-determining step was the diffusion of the ions to form a solventseparated ion pair, followed by rapid desolvation to form the contact ion pair. Measured association rate constants were very nearly those predicted for a diffusion-controlled process.     

Identification of proton type in concentrated sweet solutions by pulsed NMR analysis

The spin-spin proton relaxation times T₂ of concentrated sucrose, maltose,D-glucose andL-proline solutions were determined using a Bruker Minispec NMR Spectrometer. Log spin echo amplitude decay curves were also determined and their non-linear nature allowed the proportions of different proton types to be calculated. These were in agreement with the theoretical proportions of ring (non-exchangeable protons), solute hydroxyl protons and water protons in the simple sugar molecules. A deuteration experiment confirmed that only non-exchangeable ring protons remained.     

Phosphorylated amino acids: model compounds for solid-state 31P NMR spectroscopic studies of proteins

Solid-state 31P NMR spectroscopy was applied to measure the isotropic chemical shifts, chemical shift anisotropies and asymmetry parameters of three phosphorylated amino acids, O-phospho-L-serine, O-phospho-L-threonine and O-phospho-L-tyrosine. The cross-polarization buildup rates and longitudinal relaxation times of 31P and 1H were-determined and compared with the values measured for a triphosphate (GppCH2p) bound to a crystalline protein (Ras). It is shown that the phosphorylated amino acids are well-suited model compounds, e.g. for the optimization of experiments on crystalline proteins. Two-dimensional exchange experiments on O-phospho-L-tyrosine indicate the existence of an exchange between the two different conformations of the molecule.     

Polymerization,structure and thermal properties of ODPA-DMB polyimide films

A new high molecular weight polyimide based on 4,4-oxidiphthalic anhydride (ODPA) dianhydride and 2,2-dimethyl-4,4-diaminobiphenyl (DMB) diamine has been synthesizedvia a one-step polymerization method. This polyimide is soluble in phenolic solvents. Films from 7 to 30 m thick were cast from the polymer solution and show in-plane orientation on a molecular scale detected by Fourier transform infrared spectroscopy experiments. This anisotropic structure leads to anisotropic optical properties arising from two different refractive indices along the inplane and out-of-plane directions. ODPA DMB possesses high thermal and thermo-oxidative stability. The glass transition temperature has been determined to be 298 °C. Dynamic mechanical analyses show two relaxation processes appearing above room temperature: the - and the -relaxation processes. The -relaxation corresponds to the glass transition while the -relaxation is a secondary relaxation process associated with the non-cooperative subsegmental motion.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayYHK acknowledges the support from the Yonam Foundation, Korea. This work was also supported by the Center of Molecular and Microstructure of Composites (CMMC) of NSF/EPIC/Industry, SZDC gratefully acknowledges the support from his PYI Award (DMR-9157738) from the National Science Foundation.     

交联网络和浓溶液中高分子链运动的NMR研究 Ⅱ质子自旋-自旋弛豫与凝胶和浓溶液体系中高分子链段运动

用自旋－自旋弛豫时间考察了线型聚苯乙烯溶液与溶胀交联聚丙烯酰胺－丙烯酸凝胶的质子弛豫行为。发现在溶胀交联体系中，不论交联度高低，聚丙烯酰胺－丙烯酸质子的弛豫时间弛豫都呈现出双指数衰减特征；而在线型溶液体系中，聚苯乙烯质子的弛豫时间弛豫符合单指数衰减特征。说明在线性聚苯乙烯溶液中，高分子的链段运动是一种均匀行为，而在溶胀交联聚丙烯酰胺－丙烯酸体系中，不论交联度高低，高分子链段运动始终存在快慢不同的两部分。     

高温热处理对偏氟乙烯-四氟乙烯共聚物高次结构的影响

聚偏氟乙烯(PVDF)及其一些共聚物,例如偏氟乙烯-四氟乙烯共聚物(PVDF/TFE)经过处理后呈现较强的压电性。许多研究表明它们是铁电聚合物,而且压电活性与样品的高次结构有关。松弛谱是研究结晶高聚物的高次结构的有力工具,近来,Koizumi等人报道了PVDF/TFE的热处理与松弛现象的关系。本文作者也报道了     

Structure of microemulsions of AOT and water in dodecane

The dielectric properties of the system water/AOT/dodecane are studied as a function of volume fraction of the dispersed phase and molar ration (water/surfactant). Data shows that the spherical model is valid only at lown values or low values. At high concentrations of dispersed phase, one has to consider micellar aggregation or deformation.