Compositional Dependence of Static Shear Viscosity of Immiscible PP/PS Blends

Phase structures of immiscible polypropylene (PP)/polystyrene (PS) blends with different volume proportions, PP90/PS10, PP80/PS20, PP70/PS30, PP60/PS40, PP50/PS50, PP40/PS60, PP30/PS70, PP20/PS80, PP10/PS90, were observed by means of scanning electronic microscopy (SEM). The zero shear viscosities of the blends were determined according to a modified Carreau model by fitting the curves of static shear rate sweeps of blends tested at 190°C in a Stress Tech Fluids Rheometer. The results showed that the compositional dependence of zero shear viscosity of PP/PS deviated greatly from linear or log‐linear additivity. When PS was dispersed in a PP continuous phase, the blends showed negative deviation, while for blends with PP dispersed in a PS matrix, positive deviation was generated. When different theoretical equations of Nielsen, Utracki, Taylor, Frankel‐Acrivos (FA), Choi‐Schowalter (CS), and Han‐King (HK) were used to fit the experimental data of zero shear viscosities of blends, none of them was suitable for PP/PS blends. These experimental phenomena may result from the complex phase structures of the blends and their response to shear conditions, which are discussed in detail and compared with the experimental analysis.     

Preparation and Surface Properties of Fluorinated Acrylates Copolymers

Copolymerization of acrylates and styrene (St) with perfluorooctylacyloxyethyl methacrylate (FA) monomer, prepared from the reaction of perfluorooctanoic acid and hydroxymethyl methacrylate, was carried out by solution polymerization. The fluorinated acrylate and St copolymers (PFA) were examined by GPC, FT-IR, and ¹H NMR. The surface tension of the PFA solution in N-methyl pyrrolidone was tested by the drop volume method. The results showed that the surface tension of the PFA solution decreased in exponential decay with increase of the PFA concentration, and the surface tension of the solution also decreased with increased addition of the FA monomer in the copolymer at the same concentration. Meanwhile, the adsorption of the PFA macromolecules in the air–solution interface increased and enrichment of the fluorinated segments on the solution surface occurred. The studies of the surface free energy, polarity, fluorine content, and morphology of the PFA films illustrated that the surface free energy and polarity of the PFA films were decreased with the augment of the FA monomer in the copolymers, and that the fluorine content and the surface roughness were increased. The surface free energy of the PFA film was as small as 16.6 mN·m^?1. The surface properties of the PFA copolymers obtained by one shot feed during polymerization were superior to those obtained by continuing feed procedure. More fluorine segregation occurred and induced the formation of a fluorine-enriched surface if the PFA copolymer was postheated. The posttreatment was thus beneficial to the improvement of the surface properties of the PFA film.     

Investigation of formation mechanism of Ti3SiC2 by high pressure and high-temperature synthesis

ABSTRACT

In this paper, synthesis of titanium silicon carbide (Ti₃SiC₂) under high pressure and high-temperature condition has been investigated by using the reactant systems Ti/Si/C, Ti/SiC/TiC, Ti/SiC/C and Ti/TiC/Si. Results reveal that Ti/TiC/Si is unsuited to the synthesis of Ti₃SiC₂ under a high pressure of 2.0?GPa, while an elemental mixture of Ti/Si/C is applicable. By the addition of Al, Ti₃SiC₂ with 95.8?wt% purity was obtained from elemental mixture with a large excess of silicon. The optimum experimental parameters were determined as Ti/Si/Al/C having the molar ratio of 3:1.5:0.5:1.9, holding at 2.0?GPa and 1300?°C for 60?min.     

Assessment of dynamic closure for premixed combustion large eddy simulation

Turbulent piloted Bunsen flames of stoichiometric methane–air mixtures are computed using the large eddy simulation (LES) paradigm involving an algebraic closure for the filtered reaction rate. This closure involves the filtered scalar dissipation rate of a reaction progress variable. The model for this dissipation rate involves a parameter β_c representing the flame front curvature effects induced by turbulence, chemical reactions, molecular dissipation, and their interactions at the sub-grid level, suggesting that this parameter may vary with filter width or be a scale-dependent. Thus, it would be ideal to evaluate this parameter dynamically by LES. A procedure for this evaluation is discussed and assessed using direct numerical simulation (DNS) data and LES calculations. The probability density functions of β_c obtained from the DNS and LES calculations are very similar when the turbulent Reynolds number is sufficiently large and when the filter width normalised by the laminar flame thermal thickness is larger than unity. Results obtained using a constant (static) value for this parameter are also used for comparative evaluation. Detailed discussion presented in this paper suggests that the dynamic procedure works well and physical insights and reasonings are provided to explain the observed behaviour.     

Analytical predictions of shapes of laminar diffusion flames in microgravity and earth gravity

Flame shape is an important observed characteristic of flames that can be used to scale flame properties such as heat release rates and radiation. Flame shape is affected by fuel type, oxygen levels in the oxidiser, inverse burning and gravity. The objective of this study is to understand the effect of high oxygen concentrations, inverse burning, and gravity on the predictions of flame shapes. Flame shapes are obtained from recent analytical models and compared with experimental data for a number of inverse and normal ethane flame configurations with varying oxygen concentrations in the oxidiser and under earth gravity and microgravity conditions. The Roper flame shape model was extended to predict the complete flame shapes of laminar gas jet normal and inverse diffusion flames on round burners. The Spalding model was extended to inverse diffusion flames. The results show that the extended Roper model results in reasonable predictions for all microgravity and earth gravity flames except for enhanced oxygen normal diffusion flames under earth gravity conditions. The results also show trends towards cooler flames in microgravity that are in line with past experimental observations. Some key characteristics of the predicted flame shapes and parameters needed to describe the flame shape using the extended Roper model are discussed.     

Microplasma Technology and Its Applications in Analytical Chemistry

Abstract

This review article describes some existing microplasma sources and their applications in analytical chemistry. These microplasmas mainly include direct current glow discharge (DC), microhollow-cathode discharge (MHCD) or microstructure electrode (MSE), dielectric barrier discharge (DBD), capacitively coupled microplasmas (CCμPs), miniature inductively coupled plasmas (mICPs), and microwave-induced plasmas (MIPs). The historical development and recent advances in these microplasma techniques are presented. Fundamental properties of the microplasmas, the unique features of the reduced size and volume, as well as the advantageous device structures for chemical analysis are discussed in detail, with the emphasis toward detection of gaseous samples. The analytical figures of merit obtained using these microplasmas as molecular/elemental-selective detectors for emission spectrometry and as ionization sources for mass spectrometry are also given in this review article.     

带有动力学条件的高维一相Stefan问题

本文我们证明了带有动力学条件的高维一相Ｓｔｅｆａｎ总题局部古典解的存在唯一性。     

Existence of a Weak Solution for the Phase Change Problem with Joule's Heating

A phase change problem with Joule's heat ing describes tbe processes of electric heating in a conducting material. It is modeled as a coupled system of nonlinear partial differential equations with quadratic growth in the gradient. We establish the existence of a weak solution for the problem in two dimensions.     

二阶Melnikov函数及其应用

在Ｍｅｌｎｉｋｏｖ函数的种种应用中，目前常见到的仅是一阶形式。本文具体推导了二阶Ｍｅｌｎｉｋｏｖ函数的分析表达，提出了临界情况下考察双曲鞍点的稳定流形与不稳定流形相对位置的二阶判据，并成功地用于环面ｖａｎｄｅｒＰｏｌ方程的研究中。