分子量对聚丙烯等温结晶的影响

<正> 在高聚物结晶动力学的研究中,分子量对结晶速率的影响是一个有实际意义和理论兴趣的研究课题,由于聚烯烃可以得到分子量变化范围相当宽(MW从10~3到10~6)的试样,因而它是研究结晶速率分子量依赖性较合适的对象,其中研究最多的是聚乙烯和聚丙烯。从前入的研究报道看来,影响聚丙烯结晶速率的因素比聚乙烯要复杂。除了聚丙烯可生成多种晶型结构,会影响其结晶速率以外,用不同聚合方法制备的试样,由于其链结     

Features and origin of the dynamic and the nonlinear piezoelectricity in poly(vinylidene fluoride)

Some of the piezoelectric coefficients of poly(vinylidene fluoride) are distinctly stress dependent. We report on their dependence on the frequency of an oscillatory stress excitation, on the amount of the remanent polarization in the sample materials, and on the magnitude of an offset stress. In order to explain the observed dynamic and nonlinear piezoelectric properties, a model is developed that attributes them to changes in the local polarization in an interphase between the crystalline and amorphous phases in this semicrystalline polymer.     

Dynamic complexity of optimal paths and discount factors for strongly concave problems

We study the relationship between the dynamical complexity of optimal paths and the discount factor in general infinite-horizon discrete-time concave problems. Given a dynamic systemx _t+1=h(x _t ), defined on the state space, we find two discount factors 0 < ^{* **} < 1 having the following properties. For any fixed discount factor 0 < < ^*, the dynamic system is the solution to some concave problem. For any discount factor ^** < < 1, the dynamic system is not the solution to any strongly concave problem. We prove that the upper bound ^** is a decreasing function of the topological entropy of the dynamic system. Different upper bounds are also discussed.This research was partially supported by MURST, National Group on Nonlinear dynamics in Economics and Social Sciences. The author would like to thank two anonymous referees for helpful comments and suggestions.     

Conductance of potassium halides near the temperature of maximum density of water

The conductances of dilute aqueous solutions of KCl, KBr, and KI have been measured over the temperature range 2 to 8°C and have been analyzed by the Fuoss-Hsia equation. The ionic Walden products at infinite dilution have been discussed in terms of local viscosity. The temperature dependence of these products suggest that near the temperature of maximum density of water, the structure-breaking ability of these ions changes in a regular way.     

Volumetric study on the inclusion complex formation of α- and β-cyclodextrin with 1-alkanols at different temperatures

The partial molar volumes (V_a) of 1-alkanols (carbon number, m=5, 6, 7) in - and -cyclodextrin (CD) solutions at 5.00 mmol kg^–1 have been determined as a function of alkanol concentration (C_a) between 293.2 and 308.2 K by using a dilatometer. It has been observed that with an increase in C_a, V_a increased in -CD solution but decreased in -CD solution, asymptotically to a value of V_a in CD-free water. The dependence of V_a on C_a provided the binding constant (K) of 1:1 complex, the volume change in complex formation, and the partial molar volume of complex itself. The complex formation mechanism has been discussed on the basis of these values and their carbon number dependences in the respect of geometric behavior, hydrophobic interaction, and van der Waals interaction. It is concluded that the CD cavity in water is not rigid but flexible for fitting in nicely with guest molecule.     

Binding Reaction of Hemin with Chloroquine, Quinine and Quinidine in Water-propylene Glycol Mixture

the interaction of hemin with chloroquine,quinine and quinidine was investigated in 50% water-propylene glycol mixture at pH=9,8.1,7.4 and 6.8using a spectrophotometric method.The data could be well fitted into a model consistent with the formation of a 1:1 complex between the reacting partners.In addition,the results indicated that hemin complexed more strongly with quinidine than with chloroquine and quinine,and the binding constants were pH-dependent.Moreover,it was proved that the water-propylene glycol mixture is well suitable to the study of the systems containing hemin and quinolinebased drugs.     

Additivity Factors in the Binding of the Diethyltin(IV) Cation by Ligands Containing Amino and Carboxylic Groups at Different Ionic Strengths

Complex formation constants were determined potentiometrically (by a ISE-H⁺, glass electrode) in the systems, M²⁺ – L^z – H⁺ [M²⁺ = (C₂H₅)₂Sn²⁺, L^z = malonate, glycinate and ethylenediamine] at t = 25 ^∘C and 0.1 mol-L⁻¹≤ I/ ≤ 1 mol-L⁻¹ in NaCl_aq (0.1 mol-L⁻¹ ≤ I ≤ 0.75 mol-L⁻¹ for the ethylenediamine system). Thermodynamic values of formation constants, at infinite dilution, are [± 95% confidence interval, ^Tβ_pqr refer to the equilibrium, pM²⁺ + qL^z + rH⁺ = M_pL_qH_r^(2+z+r)]: for malonate, log₁₀ ^Tβ₁₁₀ = (5.47 ± 0.10); for glycinate, log₁₀ ^Tβ₁₁₀ = (9.54 ± 0.08), log₁₀ ^Tβ₁₁₁ = (12.97 ± 0.10); and for ethylenediamine, log₁₀ ^Tβ₁₁₀ = (10.47 ± 0.10), log₁₀ ^Tβ₁₂₀ = (16.17 ± 0.12) and log₁₀ ^Tβ₁₁₁ = (15.46 ± 0.10). The dependence on ionic strength of the formation constants was modeled by a simple Debye–Hückel type equation and by the SIT approach. By analyzing the stability of the species in the three different systems we found a simple additivity rule that can be expressed by the relationship: log₁₀ K = 6.46 n_N + 3.96 n_O − 0.60 (n_N²+ n_O²), with a mean deviation, ε(log₁₀ K) = 0.15 (K = equilibrium constant for the interaction of the organometal cation with the unprotonated or protonated ligand, n_N = number of amino groups and n_O = number of carboxylic groups of the ligand(s) involved in the formation reaction of complex species).     

Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997.     

Pressure and volume dependence of thelo-to phonons in InAs

The pressure dependence of thelo-to phonons in InAs has been investigated by Raman scattering using the diamond anvil cell. Indium arsenide transforms, presumably to the rock-salt structure at 70±1 kbar. The mode Grüneisen parameters for thelo-to phonons are γ _lo =0.99±0.03, γ _to =1.2±0.03 respectively. The effective charge,e* _T , for InAs decreases slightly with pressure and this trend is in accordance with the behaviour of other III–V zinc blende structured semiconductors: The structural phase transition is discussed in the light of theoretical calculations for phase stability of III–V compounds, as well as recent high pressure x-ray diffraction studies.     

The solubilization of alcohols in micellar solutions

The specific conductivities of dodecyldimethylbenzylammonium bromide (C12BBr) have been determined in aqueous butanol and aqueous benzyl alcohol solutions in the temperature range of 5-40°C. From these data the temperature dependent critical micelle concentration (cmc) was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The thermal properties such as standard Gibbs free energy, enthalpy and entropy of solubilization of alcohols in the micelles were estimated for the phase separation model. The change in heat capacity upon solubilization of alcohol in the micelle has been estimated form the above properties. This revised version was published online in July 2006 with corrections to the Cover Date.