Mechanical structures in polymer melts. I. Measurements of melt strength and elasticity

The standard methods of measuring the elastic properties of polymer melts are briefly reviewed and a method of measuring another combination of viscoelastic properties, the melt strength, is described. Data are presented on the melt strength of various types of polyethylene resins and on ionomer resins. The effects on various viscoelastic properties of branching or of the addition of fine fibrils of Teflon perfluorocarbon resin are reported.     

Thermal diffusivity measurement of polyethylene melt by a new temperature wave method

Thermal diffusivity of high density polyethylene (PE) has been measured by a new a. c. Joule-heating method. The diffusivity was determined at various temperatures between room temperature and above melting point in heating and cooling processes. This method is based on the phase shift of temperature waves across film sample, so that it offers several advantages, e.g., easy measuring in polymer melts.     

Schmelzindexbestimmung mit einem automatischen Prüfgerät

A semi-automatic procedure is described for measuring the melt-flow index of thermoplastic material. The piston rate, expressed as a sequence of pulses, is taken as a measure for the extrusion rate. The melt-flow index is indicated digitally and registered. In addition to routine melt-flow index determinations, the device allows investigations of the flow behaviour of plastic melts as a function of time as well as of viscoelastic phenomena. Examples are given to illustrate advantages and uses of the device.     

Stress Relaxation in Polymer-Modified Bitumens

The efficiency of BNK-40/180 bitumen modification with a blended thermoelastoplast and its components is studied by measuring the kinetics of the stress relaxation in melts. Asphaltene agglomerates are disclosed to be the main kinetic units of the stress relaxation in bitumens and bitumen–polymer compositions. The efficiency of bitumen modification with polymers is mainly affected by the solubility of the latter in the malthene fraction and their adsorption on asphaltenes. The experiments performed made it possible to estimate the behavior of modified bitumens at low shear rates corresponding to the extreme conditions of their use.     

LiFeO_2包覆MCFC氧化镍阴极的制备及性能研究

以硝酸锂和硝酸铁为原料 ,柠檬酸作燃料 ,采用燃烧合成法制备了铁酸锂包覆的多孔氧化镍阴极 .X_射线衍射技术 (XRD)、X_射线能量散射谱 (EDAX)和电子显微镜 (TEM和SEM )分析表明 ,在氧化镍颗粒表面的包覆层是由直径小于 10 0nm的铁酸锂微粒所构成 ,并与氧化镍颗粒紧密烧结在一起 ,有效地减少了氧化镍与熔融碳酸盐的接触面积 ,从而降低了氧化镍的溶解度 .同时 ,本文还研究了该阴极在熔融碳酸盐燃料电池中的电性能 ,并与未包覆的NiO阴极进行比较     

Falling sphere viscometry in gravitational and magnetic fields

The classical falling sphere method based onStokes' law is well known. Using gravitational forces, however, restricts the range of measurements considerably. This advantage can be overcome by applying iron spheres in a magnetic field, which allows to measure polymer melts with viscosities up to ₀=10⁹ Pa s (with very strong magnets available even more). A special measuring cell designed for application in the magnetic field is tested with several silicon oils in the gravitational field too. In both cases wall and end corrections toStokes' law have to be considered and are of main concern. Another important point is a reliable temperature measurement. Results especially for the high viscosity region of polymer melts are given.Herrn Prof. Dr.K. Komarek zum 60. Geburtstag gewidmet.     

Optical properties and redox state of silicate glass melts

Advanced experimental techniques to measure the spectral absorption and oxidation state of silicate glass melts are described. Exemplary results of the characterisation of industrial glass melts by these two methods are presented. The technological impact of the high-temperature optical properties and oxidation state of glass melts on radiative heat transfer and on the final glass colour is discussed.     

The abnormal changes of electrical resistivity in liquid Pb–In alloys

Electrical resistivity of liquid lead and indium (Pb–In) alloys with different compositions has been measured using the four-probe method in a large temperature range. Marked turning points on each resistivity–temperature (ρ–T) curve of the liquid Pb–In alloys can be observed far above the liquidus. The unusual variation of the resistivity of Pb–In melts suggests a structural transition of these melts, for resistivity is a sensitive parameter to the structure. Moreover, the DSC experiment of Pb–In melts supports the existence of a liquid–liquid (L–L) structure transition in Pb–In melts. Such a L–L structural transition can be described in terms of the gradual disappearance of atomic bonds corresponding to the crystal structure and/or to a reduction of the size of pre-formed atomic clusters. This implies an increase of disorder in the high temperature melts. The transition temperatures depend on the composition of Pb–In melts and the onset transition temperatures of the intermediate phase (α) Pb–63%In and Pb–70.6%In melts are higher than that of other compositions.     

Chemie der Seltenen Erden in geschmolzenen Alkalihalogeniden. X. Schmelzen von Alkalichloriden mit Neodymchlorid und Gadoliniumchlorid

Molvolume measurements of homogenous melts of the systems NdCl₃–CsCl and GdCl₃–NaCl, –KCl, –CsCl result in isotherms, which characteristics may be explained by the assumption of complex species in the melt. This interpretation will be discussed in connection with the phase diagrams. The accuracy of the described measuring device is demonstrated. Furthermore, the density of molten GdCl₃ and controlling measurements of the systems KCl–KBr as well as NaCl–RbCl are described.     

云母表面上低分子量聚氧乙烯熔体的“假不浸润”行为

在固体基底表面上,液体可以表现出不同的浸润性.若完全浸润,液体会铺展成膜;若部分浸润或不浸润,液体则会聚集成团.和上述经典的浸润行为不同,“假不浸润”(pseudo-dewetting)是一种比较特殊的现象,引起了人们的广泛关注.1955年Hare和Zisman[1]发现,将许多极性、两亲性和不稳定     

Formation of short-range order in Al–Ge–Fe melts: influence of composition

ABSTRACT

The short-range order in Al–Ge–Fe melts has been studied by X-ray diffraction and reverse Monte Carlo simulations in wide concentration range. Influence of the replacement of one component by another while the content of third component is constant on the formation of a local structure of ternary melts has been discussed. It has been shown that at Ge content less than 30 аt. % Ge atoms are uniformly distributed in the volume of the Al–Ge–Fe melts and atomic clusters with structure similar to the liquid germanium are formed at content more than 30 аt. % Ge. The addition of the third component (Ge or Al) to the binary Al–Fe or Fe–Ge melts, correspondingly, results in competition between Al and Ge atoms in formation of the local structure around Fe atoms. The obtained concentration dependences of the nearest neighbour distances point out that the ternary interactions take place in the Al–Fe–Ge melts.     

Measurements of dynamic interactions in thin films of polymer melts: The transition from simple to complex behavior

Two techniques are described for measuring the shear viscosities of thin liquid films confined between two surfaces. Both techniques employ the surface forces apparatus, which has already been used extensively to measure the static interactions between surfaces in liquids. With either of the new dynamic techniques, shear viscosities of the confined liquids can be measured as a function of film thickness with a precision of about 0.1 nm (1 Å). The techniques complement each other: one is used to best advantage at high shear rates, the other at low shear rates. Results are presented for measurements made on low-molecular-weight polymer melts of polybutadienes. At low shear rates, these results provide detailed information on the relation between polymer molecular weight, the conformation of polymer molecules at the surfaces, the intermolecular forces between the surfaces, and the location of the shear plane (plane of no-slip). At high shear rates, the results suggest the gradual evolution of non-Newtonian behavior in submicron liquid films.     

聚合物熔体界面扩散理论与研究方法

本文结合与聚合物加工过程密切相关的界面扩散问题,从动力学和热力学两方面综述了与聚合物界面互扩散相关的基础理论.结合在聚合物界面扩散方面的研究进展,系统介绍了聚合物熔体界面扩散的常用研究方法.对其中的流变学方法的原理及进展作了重点论述,该方法不仅可以有效表征聚合物熔体界面扩散的动力学过程,进一步从分子动力学角度发展并完善聚合物扩散理论,而且对于聚合物加工成型过程的界面结构设计和性能优化起到关键的指导作用.本文最后提出了聚合物熔体界面扩散研究中存在的问题并对其前景进行了展望.     

Recent Results in the Field of Liquid Crystals

Thermotropic mesomorphous phases such as occur in the melts of many organic substances are considered. Though mesomorphous melts were first observed by Reinitzer in 1888, fundamental structural problems regarding such melts have not, as yet, been completely solved. Part I of this article deals mainly with such structural problems and with the theories of crystalline organic liquids. Part II describes the use of nematic solvents for magnetic resonance studies on oriented molecules. Examples are given to illustrate the possibilities offered by this procedure, and some of the results obtained so far are reviewed.     

High-voltage electroconduction in molten chlorides of alkaline-earth metals

Effects of high-voltage pulses on electroconduction of molten chlorides of alkaline-earth metals and their mixtures with potassium chloride are studied experimentally. It is established that the electroconductivity of the melts subjected to the pulses increases proportionally to the voltage amplitude and the number of activating pulses in a pulse series. Oscillatory relaxation of nonequilibrium melts is discovered.     

In situ freezing point determination of cryolite baths utilising resistometer measurements

Now close to 30 years ago, Stephen Fletcher developed an instrument that measures uncompensated resistance simultaneously with electrochemical measurements and referred to that instrument as a “resistometer”. In this current work, the resistometer is modified to simultaneously measure the resistance (between the cathode and anode) and the capacitance (which is a combination of the interfacial capacitance of the cathode in series with the interfacial capacitance of the anode) in a Hall–Héroult simulator cell during cooling of a molten cryolite bath. A range of experiments with differing amounts of excess AlF₃ are carried out to investigate the effect on the freezing points of the bath. As the bath cools through different freezing events (of the multiple components of the bath), the resistance increases and the capacitance decreases giving valuable information about the freezing behaviour of different compositions of cryolite melts, which has implications for low temperature melts and the investigation of the frozen ledge behaviour in Hall–Héroult cells.     

The Rheology of Linear and Long-chain Branched Polymer Melts

By generalising the Doi-Edwards tube model to the Molecular Stress Function theory, the non-linear rheology of polymer melts can be described quantitatively. The strain-hardening of linear polymer melts in extensional flows can be accounted for by a strain energy function, which reflects the increase of strain energy due to tube squeeze. In comparison to linear polymer melts, long-chain branched polymer melts show enhanced strain-hardening. This is due to the fact that while the backbone of the branched macromolecule is stretched by deformation, side chains are compressed. It is demonstrated that the experimentally observed slope of the elongational viscosity after inception of strain-hardening depends on the ratio β of total molar mass to backbone molar mass as predicted by the model. The steady-state (plateau) value of the elongational viscosity depends on the maximum relative stretch, , which can be supported by chain segments and which represents the maximum elastic energy storable in the polymeric system.     

Electrical conductivity and IR spectra of molten benzoic acid

Impedance method was used to measure the electrical conductivity of benzoic acid melts, and the concentration of free protons in these melts was estimated. IR spectroscopic data are presented and the existence of benzoic acid in melts in the form of molecules is suggested.     

Concentration fluctuations and the heat capacity of overcooled melts in the Fe-B system

Concentration fluctuations, excess configurational entropies, and excess configurational heat capacities of melts in the Fe-B system are calculated at different temperatures. It is shown that concentration fluctuations play an important role in the amorphization of melts and should be considered in an analysis of the propensity of melts for amorphization.