Melting of polymers by non-isothermal, temperature-modulated calorimetry: analysis of various irreversible latent heat contributions to the reversing heat capacity

This paper provides an analysis of contributions to the apparent, reversing heat capacity when measured by temperature-modulated differential scanning analysis (TMDSC) with an underlying heating rate in the temperature range where irreversible transitions with latent heats occur. To deconvolute the data of a TMDSC scan into a total and reversing part, it is common practice to use the sliding averages and the first harmonics of the Fourier series of temperature and heat-flow rate. Under certain conditions, this procedure produces erroneous reversing contributions which are detailed by experiment and simulation. Unless the response to the temperature modulation is linear, the total heat-flow rate is stationary, and the transition is truly reversible and occurs only once during the temperature scan, one cannot expect a true deconvolution of total and reversible effects. In the presence of multiple, irreversible transitions within a modulation period, however, each process involving latent heat can increase the modulation amplitude, as demonstrated by computer-simulation of polymer melting. As a result, the multiple transitions may give erroneously high latent heats when integrating the apparent reversing heat capacity with respect to temperature.     

PBT／PET共混体系的熔融行为

用差示扫描量热法（ＤＳＣ）考察了ＰＢＴ／ＰＥＴ共混体系的结晶熔融行为，在共混体系中两组份的结晶熔上均随着含量的减小而下降，熔点下降既有形结构变化因素，又有因两组份相容而引起的热力学因素。熔融热焓△Ｈｍ的变化与两组份结晶熔点的变化有相似的规律。这些结果说明在共混体系中ＰＥＴ、ＰＢＴ两组份在结晶一熔融过程中存在相互协同作用，同时也说明ＰＢＴ、ＰＥＴ两组份是晶相分离的，而非晶区是相混容的。     

UNUSUAL CRYSTALLIZATION AND MELTING PROCESSES OF AN OPTICALLY ACTIVE POLYOLEFIN： ISOTACTIC POLY（（S）-4-METHYL-HEXENE-1）

Polyolefins that bear a chiral side chain (typically an isobutyl group) experience a so-called macromolecular amplification of chirality: the chiral side-chain induces a slight preference for either tg or tg- main chain conformation. This slight conformational bias is amplified cooperatively along the chain, and results in preferred chirality of the main chain helical conformations. As a result, these polymers display a liquid-crystal (LC) phase both in solution and, in the melt as a transient phase on the way to crystallization. The existence of two processes (melt-LC and LC-crystal transitions) results in unconventional behaviors that were first analyzed by Pino and collaborators back in 1975. These polymers also offer a means to test the structural consequences of recently introduced crystallization schemes. These schemes postulate the formation of a transient liquid-crystal phase as a general scheme for polymer crystallization.     

Thermophysical properties of SrHfO3 and SrRuO3

Polycrystalline samples of strontium series perovskite type oxides, SrHfO₃ and SrRuO₃ were prepared and the thermophysical properties were measured. The average linear thermal expansion coefficients are 1.13×10⁻⁵ K⁻¹ for SrHfO₃ and 1.03×10⁻⁵ K⁻¹ for SrRuO₃ in the temperature range between 423 and 1073 K. The melting temperatures T_m of SrHfO₃ and SrRuO₃ are 3200 and 2575 K, respectively. The longitudinal and shear sound velocities were measured by an ultrasonic pulse-echo method at room temperature in air, which enables to evaluate the elastic moduli and Debye temperature. The heat capacity was measured by using a differential scanning calorimeter, DSC in high-purity argon atmosphere. The thermal diffusivity was measured by a laser flash method in vacuum. The thermal conductivities of SrHfO₃ and SrRuO₃ at room temperature are 5.20 and 5.97 W m⁻¹ K⁻¹, respectively.     

CaF2熔化温度的分子动力学模拟

The molecular dynamics method has been applied to simulate the melting temperatures of CaF 2 at elevated temperature and high pressure and to calculate the P～V equation of state of CaF 2 up to 100 GPa at 300 K. The interatomic potential was taken to be the sum of pairwise additive Coulomb, van der Waals attractions, and repulsive interactions. In addition, the shell model was used in molecular dynamics simulation. The pressure dependence of the melting temperature of CaF 2 was predicted up to 4 GPa. However, in order to account for the superheating melting of the molecular dynamic simulation, the simulated melting temperatures of CaF 2 were corrected by the modern theory of melting. Consequently, the melting temperatures of CaF 2 were accurately obtained at elevated temperature and high pressure. Therefore, it is shown that shell model molecular dynamics simulation at constant pressure indeed provides a useful tool for studying the melting temperatures of other materials under high pressures.     

到复Grassmann流形的多重调和映照的构造

本文给出了一些到复Ｇｒａｓｓｍａｎｎ流形的多重调和映照的构造定理,从而推广了莫小欢,Ｂｕｒｓｔａｌｌ　Ｆ． Ｅ．,Ｗｏｏｄ Ｊ． Ｃ．和 Ｕｄａｇａｗａ Ｓ．的结果．     

Cellularity of a New Class of Diagram Algebras

A diagram algebra in which the diagrams include n rows of n points is constructed. Moreover, we prove that the algebra is cellular and quasi-hereditary.     

Computation of melting with natural convection inside a rectangular enclosure heated by discrete protruding heat sources

This paper presents the results of a numerical investigation of the heat transfer by natural convection during the melting of a phase change material (PCM, n-eicosane with melting point of 36 °C) contained in a rectangular enclosure. This latest is heated by three discrete protruding heat sources (simulating electronic components) placed on one of its vertical walls. The power generated by heat sources is dissipated in PCM. The advantage of using this cooling scheme is that the PCMs are able to absorb high amount of heat generated by the heat sources, without acting the fan during the charging process (melting of the PCM). The thermal behavior and thermal performance of the proposed PCM based-heat sink are numerically investigated by developing a mathematical model based on the mass, momentum and energy conservation equations. The obtained numerical results show the impact of various key parameters on the cooling capacity of the PCM-based heat sink. Correlations encompassing a wide range of parameters were developed in terms of the dimensionless secured operating time (time required by one of the electronic components before reaching its critical temperature, T_cr ∼ 75 °C) and the corresponding liquid fraction, using the asymptotic computational fluid dynamics (ACFD) technique.     

Collapsed and Adsorbed States of a Directed Polymer Chain in Two Dimensions

A phase diagram for a surface-interacting long flexible partially-directed polymer chain in a two-dimensional poor solvent, where the possibility of collapse in the bulk exists, is determined using exact enumeration methods. We used a model of self-attracting self-avoiding walks and evaluated 30 steps in series. An intermediate phase between the desorbed collapsed and adsorbed expanded phases, having the conformation of a surface-attached globule, is found. The four phases, viz ., (i) desorbed expanded (DE), (ii) desorbed collapsed (DC), (iii) adsorbed expanded (AE), (iv) surface-attached globule (SAG), are found to meet at a multicritical point. These features are in agreement with those of an isotropic (or non-directed) polymer chain.     

Non-extensive thermostatistics approach to metal melting entropy

A generalized Mott relation of metal melting entropy is derived by means of non-extensive solid and liquid quantum entropy that we calculate from grand partition functions of the localized ordered quantum solid and of the disordered quantum Boltzmann liquid. For each of the 18 elements considered, the entropic parameter _qm$q_m$, depending on particle correlations, is deduced such that a better agreement is obtained between calculated non-extensive metal melting entropy and available experimental data. The non-extensive entropic parameter makes the difference between normal and anomalous metals. Therefore, those elements not reported here should also belong to one of the two classes. Possible applications to condensed matter, Earth, and other solar planets seismology are mentioned.