尼龙1010等温结晶球晶形态与生成条件研究

 本文利用偏光显微镜研究了等温结晶时尼龙1010球晶的形态与生成条件,发现在原始样品熔点附近或高于原始熔点以上温度结晶,主要生成暗、亮与带正环的负光性放射状球晶;熔点以下至195℃主要生成正放射状球晶;在较宽的温度范围内可生成混合光性放射状球晶,与少量的六瓣、两瓣、不对称四瓣形三种异常光性球晶;181℃以下主要生成正环状球晶.     

尼龙1010等温结晶球晶形态与生成条件研究

本文利用偏光显微镜研究了等温结晶时尼龙1010球晶的形态与生成条件,发现在原始样品熔点附近或高于原始熔点以上温度结晶,主要生成暗、亮与带正环的负光性放射状球晶;熔点以下至195℃主要生成正放射状球晶;在较宽的温度范围内可生成混合光性放射状球晶,与少量的六瓣、两瓣、不对称四瓣形三种异常光性球晶;181℃以下主要生成正环状球晶.     

尼龙1010球晶的转化

本文利用偏光显微镜研究了尼龙1010球晶的转化。发现在降温过程中放射状球晶多转变成相同光性的环状球晶。升温时正环状转化为正放射状球晶;正、混合放射球晶部分转化为负放射状球晶;黄蓝两瓣球晶在一定温度范围内可与负放射球晶相互转变。多种球晶共存时,混合放射球晶可转变成两瓣、不对称四瓣和六瓣形放射球晶;正、混合坏状分别转变成不对称四瓣和六瓣形环状球晶;最后都以环状球晶熔化。     

尼龙1010环状球晶的研究

利用偏光显微镜研究了尼龙1010环状球晶的生成条件、形态特征和光学性质,发现在等温结晶过程中只可生成环状球晶;在降温过程中可由相同光性的放射状球晶转变成正、负、混合光性环状球晶;在升温过程中正光性和混合光性环状球晶分别转变成不对称四瓣形和六瓣形环状球晶,负放射球晶可转变成另一种负环状球晶。     

间规聚苯乙烯晶体结构的研究——等温结晶球晶形态及生成条件研究

用偏光显微镜研究了 2 0 0℃～Tm 等温熔体结晶间规聚苯乙烯 (s PS)的球晶形态及其生成条件 ,发现s PS共可生成八类球晶 .在较低温度 (Tc<2 40℃ )下 ,生成大量晶片排列疏散的羽毛状球晶 ;而Tc>2 40℃时 ,生成大量晶片堆砌紧密的八瓣球晶及少量四瓣球晶 ;此外 ,2 30℃附近还有带螺旋消光环的正球晶和串晶生成     

改性羟基磷灰石/聚乳酸纳米复合材料的结晶行为

利用溶剂复合的方法制备了具有良好生物相容性的表面接枝聚(γ-苄基-L-谷氨酸)的改性羟基磷灰石/聚乳酸纳米复合材料, 并研究了其熔融与结晶行为. 结果表明, 聚乳酸的玻璃化转变温度为60.3 ℃, 而复合材料的玻璃化转变温度达到65.8 ℃, 不同样品在140 ℃等温结晶后, 改性羟基磷灰石/聚乳酸复合材料的球晶直径仅为聚乳酸(PLLA)球晶直径的16.7%~66.7%. 复合材料的熔点提高到184.4 ℃.     

聚对苯二甲酸乙二酯的结晶与取向

为了了解PET球晶的拉伸性能与球晶结构的关系以及无定形PET的取向和结晶,我们采取了两条不同的路线来制备样品:(1)先用溶液浇铸成膜的办法制备具有正球晶、负球晶或非常球晶的薄膜,然后进行单轴拉伸。电子显微图象及电子衍射证明,球晶的拉伸性能与C轴和球晶半径方向的夹角有关,夹角愈大拉伸愈困难;(2)先制备无定形的薄膜,然后在玻璃化温度附近进行单轴拉伸以获得C轴取向,再在215℃退火,使之结晶。电子衍射图证明,这样制备的样品具有高度的C轴取向。DSC结果表明,结晶的完善程度远比球晶的为高。     

反气相色谱法研究结晶聚合物的结晶行为

 :采用反气相色谱法(IGC)测定了结晶聚合物聚乙二醇(PEG)的熔点和结晶度,探讨了探针分子的性质、固定相中聚合物的涂布量对测定结果的影响,同时与热分析(DSC)方法测得的结果作了比较。结果表明,IGC法测定结晶性聚合物熔点和结晶度是一种非常实用可靠的技术,其优点在于并不依赖100%纯结晶聚合物的性质,PEG的熔点测得值为67℃,结晶度为89.7%,测定结果与DSC法的测得值(Tm=67.9℃,Xc=90.6%)相近,所测定的结果与探针分子的性质无关,但受PEG在担体上的涂布量的影响显著。     

聚全氟乙丙烯的分子聚集态结构及其对开裂性能的影响

本体结晶的全氟乙丙烯(FEP) 共聚物一般具有球晶形态结构。球晶的发展与完整程度决定于共聚物的分子结构与结晶条件,所研究的球晶尺寸在几微米至一百多微米之间。界面间的联接分子数,在试样的分子量增大和结晶温度降低时增加。它显著地影响其开裂性能。材料中联接链越多,其使用性能越好。FEP在接近其熔点温度退火,能够改善在200℃的使用性能。     

热历史对聚醚醚酮及其碳纤维复合材料——Ⅱ.熔融行为的影响

本文利用差示扫描量热仪(DSC)研究了聚醚醚酮(PEEK)和以PEEK为基体的碳纤维复合材料(APC-2)的热历史对它们熔融行为的影响。在200—315℃结晶并退火热处理后,试样的DSC曲线上出现了两个吸热峰。低温吸热峰(峰温T′_m)较小,并与结晶和退火温度(T_c)有关;高温吸热峰(峰温T_m)较大,几乎不受T_n的影响。T′_m的出现与在不同T_c下生成的不完整晶体的熔融和重结晶过程有关,而T_m的出现则与完整晶体的熔融过程有关。实验结果表明,T′_m与T_c之间呈线性关系。按文献报道的方法,将T′_m与T_c的直线外推至与T′_m=T_c直线相交,其交点温度即为平衡熔点.结果表明,PEEK和APC-2试样的“平衡熔点”受不同热历史条件下生成晶体的完整程度的影响。当结晶并退火时间越长,求出的“平衡熔点”值越低,并与理论值接近。实验结果还表明,碳纤维表面具有促进PEEK树脂基体晶体完整化的作用,因而导致APC-2试样中PEEK树脂基体的熔点高于纯PEEK树脂。     

Extrapolation of short-chain oligomers melting temperatures at infinite molecular weight

The determination of the thermodynamic equilibrium melting point of a polymer (T) by the extrapolation of the melting temperature of its oligomers has been extensively studied in the case of n-alkanes. Nevertheless, a recent publication¹ underlines the difficulty to realize this extrapolation. A new method is presented here, leading to an acceptable extrapolation of PE. The equation proposed may give a better value of T_m because the premelting phenomena is being considered in its development. Moreover, this method can be easily extended to a larger number of polymers, such as PEO, PEEK, PPS, etc.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2563–2571, 1998     

Congruent melting of binary compounds with non-negligible vapour pressure

The sulfaguanidine—water (SG-H₂O) system is a binary system with non-negligible vapour pressure which presents a monohydrate. The phase diagram of this system is drawn from DTA experimental results, using the temperature-specific volume-molar fraction (T-v-x) model which was described in part I of this work. The melting of the monohydrate (SG, H₂O) is found to be congruent. Isochoric sections are drawn; they make it possible to determine the limits of the two eutectic invariant planes. The composition and specific volume of the vapour phase at the eutectic equilibrium of theSG-SG, H₂O subsystem are given. The triple line solid-liquid-vapour of the one-component phase diagram of the monohydrate is drawn. The experimental results are consistent with the congruent melting of the monohydrate. These results also show that the solid, liquid and vapour phase at the triple line have not the same composition.     

熔点和凝固点的准确测量

介绍了英国政府化学家研究所(IGC)和兵总第204所样品的熔点和凝固点的准确测量方法,熔点和凝固点的测量结果,并进行了讨论。     

A view and a review of the melting of alkali metal halide crystals

Summary Although melting is a most familiar physical phenomenon, the nature of the structural changes that occur when crystals melt are not known in detail. The present article considers the structural implications of the changes in physical properties that occur at the melting points, T_m, of the alkali halides. This group of solids was selected for comparative examination because the simple crystal lattices are similar and reliable data are available for this physical change. For most of these salts, the theoretical lattice energies for alternative, regular ionic packing in 4:4, 6:6 and 8:8 coordination arrangements are comparable. Density differences between each solid and liquid at T_mare small. To explain the pattern of quantitative results, it is suggested that the melt is composed of numerous small domains, within each of which the ions form regular (crystal-type) structures (regliq). The liquid is portrayed as an assemblage of such domains representing more than a single coordination structure and between which dynamic equilibria maintain continual and rapid transfers of ions. T_mis identified as the temperature at which more than a single (regular) structure can coexist. The interdomain (imperfect and constantly rearranging) material (irregliq) cannot withstand shear, giving the melt its fluid, flow properties. From the physical evidence, it is demonstrated that the structural changes on melting are small: these can accommodate only minor modifications of the dispositions of all, or most, ions or larger changes for only a small fraction. This proposed representation, the set/liq melt model, may have wider applicability.     

Multiple melting behavior in isothermally crystallized poly(trimethylene terephthalate)

Melting behavior of poly(trimethylene terephthalate) (PTT) after isothermal crystallization from the melt state was studied using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques. The subsequent melting thermograms for PTT isothermally crystallized within the temperature range of 182-215 °C exhibited triple (for crystallization temperatures lower than ≈192 °C), double (for crystallization temperatures greater than ≈192 °C but lower than ≈210 °C), or single (for crystallization temperatures greater than ≈210 °C) endothermic melting phenomenon. These peaks were denoted peaks I, II, and III for low-, middle-, and high-temperature melting endotherms, respectively. For the triple melting phenomenon, it was postulated that the occurrence of peak I was a result of the melting of the primary crystallites, peak II was a result of the melting of recrystallized crystallites, and peak III was a result of the melting of the recrystallized crystallites of different stabilities. In addition, determination of the equilibrium melting temperature T_m⁰ for this PTT resin according to the linear and non-linear Hoffmann-Weeks extrapolation provided values of 243.6 and 277.6 °C, respectively.     

Effect of Molecular Mass on the Melting Temperature,Enthalpy and Entropy of Hydroxy-Terminated PEO

This paper studies the effect of molecular mass on the melting temperature, enthalpy and entropy of hydroxy-terminated poly(ethylene oxide) (PEO). It aims to correlate the thermal behaviour of PEO polymers and their variation of molecular mass (MW). Samples ranging from 1500 to 200,000 isothermally treated at 373 K during 10 min, were investigated using DSC and Hot Stage Microscopy (HSM). On the basis of DSC and HSM results, melting temperatures were determined, and melting enthalpies and entropies were calculated. Considering the melting temperatures, it was found that the maximum or critical value of MW was found around 4000, and then these remain almost constant. This behaviour was interpreted assuming that lower MW fractions (MW<4000) crystallize in the form of extended chains and higher MW fractions (MW>4000), as folded chains. The melting enthalpies showed a scattering effect at least up to MW 35,000. It was difficult to obtain any relationship between melting enthalpies in J g^–1 and MW. These variations seem to be of statistical nature. Corrected enthalpy data on a molar basis (kJ mol^–1) exhibited a linear relationship with MW. Considering the solid—liquid equilibrium, the melting entropies (in kJ mol^–1) were calculated. These values were more negative as compared with molar enthalpy increases. It was explained because the changes in melting temperatures are much smaller than those observed in the enthalpy values. Linear relationship between enthalpies andentropies as a function of MW was deduced.This revised version was published online in November 2005 with corrections to the Cover Date.     

激光诱导铝纳米膜熔化机理的分子动力学模拟

采用耦合一维双温模型的分子动力学方法研究了纳米级的铝膜在飞秒激光辐照下的熔化机制.这种方法不仅能够在原子水平上展现金属膜的各种微观行为,还能有效地描述金属膜的激光能量吸收、传递和金属电子热传导等过程.模拟结果表明,与其它金属相比,铝膜在飞秒激光辐照下的电子温度、晶格温度以及内部压力等呈现出不同的变化.铝膜在较高强度激光辐照下会很快发生全局一致的熔化,这与镍膜上下非均匀的熔化不同.并且由于铝的电子-声子耦合强度较高导致铝膜较镍膜和金膜熔化得更快.模拟结果显示,铝膜的熔化时间与实验测量的超快激光诱导的铝膜熔化时间一致.进而从理论上支持激光诱导的铝膜熔化是一个热力学熔化过程.     

Phase Equilibrium in the SeO2–Bi2O3 System

The subject of the present study is the system SeO₂-Bi₂O₃ that comprises two oxides with low melting points. All batches are thermal treatment in quartz ampoules, which are evacuated and sealed at a pressure P=0.1 Pa. On the basis of DTA (differential thermal analysis) and X-ray data, the most probable liquidus line of the system has been plotted. The eutectic composition lies about 90 mol% SeO₂,with on eutectic temperature at 230°C. Above 20 mol% Bi₂O₃ the liquidus temperature extremely increases. The formation of three compounds is proved:Bi₂Se₃O₉ and Bi₂Se₄O₁₁ are melting incongruently at 540 and 350°C respectively and Bi₂SeO₅ congruently at 915°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Memory effects in isothermal crystallization II. Isotactic polypropylene

The effects of temperature and duration of melting on the rate of isothermal crystallization of isotactic polypropylene were investigated by differential scanning calorimetry (DSC). Crystallization rates were found to decrease with increasing melt temperature and melting time. The results were discussed in the framework of the theoretical model of transient isothermal crystallization developed by the present authors [1]. The results suggest gradual destruction of predetermined nuclei with activation energyE _a=89±7 kJ/mole as a main mechanism of the observed effects.This work and Part I of this research [1] have been supported in part by Research Grant Number PB 1291/52/93/04 from State Committee for Scientific Research (KBN), Poland, and by 40% MURST founds, Italy.     

Thermochemistry of the Binary System Nitrocellulose-s-Diethyldiphenylurea

A method of gelation enthalpy determination of nitrocellulose (NC)+s-diethyldiphenylurea (Centralite 1, C1) binary system was elaborated using the change of Centralite 1 melting enthalpy in the mixture. The heats of C1 melting together with gelation and dissolution of NC fibres were determined by DSC calorimetric methods. A sharp maximum of the gelation enthalpy for C1 mole fraction x _C1 ^max =0.555 suggests that the complex is very stable and one partly nitrated anhydroglucose ring is interacting with about 1.25 C1 molecules. The gelatinization enthalpy maximum equals =−4.59 kJ mol⁻¹. This revised version was published online in August 2006 with corrections to the Cover Date.