Power law and scaling for molecular weight dependence of crystal growth rate in polymeric materials

The molecular weight (M) dependence of the linear crystal growth rate (G) and the influence of the super-cooling on the relationship between M and G were studied. The molecular weight dependence of G has been expressed generally as G∝M^α at a given super-cooling. The temperature dependence of G shows a bell shape with the maximum growth rate (G_max). The value of α was −0.5 at the temperature (T_cmax) of G_max. However, the small super-cooling and the small molecular weight gave a large negative value of α. In other words, the value of α was dependent not only on the degree of super-cooling (ΔT) but also on the molecular weight. The effect on α by these two factors (ΔT and M) goes off to zero at T_cmax and α yields to −0.5. G_max can be defined as a characteristic intrinsic value to the crystal growth behavior. The molecular weight dependence of G_max was scaled and expressed as a −0.5 power to molecular weight for all crystalline polymers.     

Electrospray of ionic precursor solutions to synthesize iron oxide nanoparticles: Modified scaling law

Existing scaling laws for electrosprays are based on particle precursors that do not affect the conductivity of the solution. A generalized scaling law for size of resultant particles obtained from electrospraying ionic precursor solutions is developed. Two different scaling expressions are derived for weak and strong electrolyte solutions based on Arrhenius expression and Kohlrausch's empirical law, respectively. The modified scaling laws are verified by comparing measured size distributions of the resultant electrosprayed aerosols generated by electrospraying aqueous and ethanol solution of ferric nitrate. The second aspect of the work is to demonstrate that narrow size distribution, nanosized iron oxide particles can be produced by thermally decomposing the resultant electrosprayed iron nitrate precursor particles. Tests were conducted in a furnace aerosol reactor (FUAR) over a range of temperatures 293-1173 K. Iron oxide particles in the range of 6-40 nm with geometric standard deviation between 1.1 and 1.3 were obtained as end product.     

Rheological properties of methylcellulose aqueous gels under dynamic compression: Frequency sweep and validity of scaling law

The aqueous methylcellulose (MC) gels are characterized with a dynamic mechanical analyzer (DMA) under dynamic vertical compression. During the frequency sweeps of MC gels at different temperatures, the storage modulus is observed to be higher than loss modulus at lower frequencies. Both of the storage and loss modulus increases with frequency, but the rate of increase is higher for loss modulus. This leads to the first crossover between E′ and E″ during the frequency scan. For the frequency scan at a high temperature (80°C), a higher rate of increase is observed in storage modulus beyond the first crossover frequency. This leads to the second crossover between storage and loss modulus. Optical microscopy results indicate the presence of core–shell microstructure in aqueous MC gels. The first crossover is possibly due to the shell–sol transition, whereas the second crossover is due to the sol–shell–core transition. The validity of scaling laws at and around the first‐crossover point (shell–sol transition) is checked. The scaling law is valid at the first‐crossover point, but it is invalid around it. Alternate scaling equations based on reduced parameters are also used to check the universality. Irrespective of temperature, scaling laws are valid for reduced parameters. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Power law models as descriptors of the kinetics of complex systems: Temperature effects

The effects of temperature on power law models for the kinetics of parallel first order systems are studied. The variation of the empirical power law parameters with temperature provides information on the relationship between the rate constant and activation energy distributions; in particular. if the power law exponent increases with temperature, there is a positive correlation between the rate constants and the activation energies; if the power law exponent decreases with temperature, there is a negative correlation between the rate constants and the activation energies; Arrhenius plots will always be concave unless the activation energies for all the reactions are equal. Application of the techniques described here to data from the catalytic cracking of gas oil over LaY zeolite reveals a compensation effect among the reacting hydrocarbon species.     

超弹性本构模型在轮胎有限元分析中的应用

对3种主要的超弹性本构模型进行对比,并基于非线性力学理论对轮胎用橡胶材料单轴拉伸力学行为进行测试;假设橡胶为完全不可压缩材料,给出Neo-Hookean,Mooney-Rivlin和Yeoh 3种超弹性本构模型常数的确定方法;在Ansys软件中采用不同的本构模型对轮胎充气状态的力学性能进行分析.结果表明,在轮胎小变形条件下,线弹性模型的模拟结果与实测值比较吻合.     

Molecular models of polymer networks and constitutive equations of rubber elasticity

Equilibrium elastic behaviour of crosslinked polymers (networks) is analysed both from the macroscopic (phenomenological) and microscopic (molecular) points of view. Molecular mechanisms possibly responsible for non-linear rubber elasticity are discussed. They include: conformational entropy of network chains at small and large extensions, hindered rotation of such chains and intra-chain point interactions, dipole-dipole interactions between asymmetric chain segments, and topological constraints leading to chain entanglement.     

基于Logistic和ARMA模型的过程报警预测

提出了一种基于Logistic回归模型和ARMA模型相结合的过程报警事件预测方法,从历史数据中提取过程报警事件序列,并分解成报警状态及报警状态的持续时间,对应建立Logistic回归模型和ARMA模型分别对其进行预测,最终实现对过程报警事件的预测。通过数值实例分析和工业过程数据进行了验证,表明该方法能够准确地预测过程报警事件。     

Ion migration law in flotation pulp and its influence on the separation of smithsonite and quartz

This study investigated the migration law of ion release and adsorption in the flotation pulp of oxide zinc ore, and found that numerous different ions existed in the pulp. The total concentrations and major sources of various ions (Pb²⁺, Zn²⁺, Fe³⁺, Ca²⁺, Mg²⁺, SO₄^2-, etc.), released from the minerals after grinding, were determined. The zeta potential tests indicated that a mixed-ion solution strongly influences the surface charge of the minerals. The flotation tests show that the migration law of ions is detrimental to the separation and concentration of minerals.     

螺杆泵定子橡胶力学试验及本构模型研究

对螺杆泵定子橡胶材料分别进行不同温度下常规与油浸介质下的单轴拉伸与平面剪切试验。基于试验数据,运用ABAQUS软件,对常规与油浸定子橡胶不同温度下的单轴拉伸与平面剪切组合的应力-应变状态分别采用M-R,Yeoh,Ogden,A-B和VDW五种本构模型进行拟合对比分析,确定出拟合效果较好的螺杆泵定子橡胶材料本构模型为Ogden模型且50℃下模型参数较优。     

The influence of temperature and strain rate on the constitutive and damage responses of polychlorotrifluoroethylene (PCTFE, Kel-F 81)

Polychlorotrifluoroethylene (PCTFE), also known as Kel-F 81, is a semi-crystalline fluoropolymer. Although it has been employed in a wide range of cryogenic components, valve seats, seals, and microelectronics packaging, its mechanical behavior has received limited coverage in the literature. In this work, we present the tensile and compressive constitutive response of PCTFE for a range of temperatures (−85 to 150 °C) and strain rates (1 × 10⁻⁴-2.9 × 10³ s⁻¹). Both large-strain experiments based on flow stress and small-strain dynamic mechanical analysis (DMA) using the elastic modulus exhibit a strong increase in the glass transition temperature, T_g, with increasing strain rate. The quasistatic fracture behavior of PCTFE is presented using J-integral fracture experiments. Finally, a discussion of the implication of the constitutive and damage responses of PCTFE on impact failure modes observed in Taylor impact experiments is presented.     

Predictive models for the viscosities of multicomponent liquid n‐Alkane and regular solutions

The pseudo‐binary model developed by Wu and Asfour (1992) has been used to modify some existing viscosity predictive models to that they can predict the viscosities of multicomponent liquid n‐alkane and regular mixtures. The McAllister three‐body interaction model and the Grunberg‐Nissan viscosity equation were both employed, after modification, to successfully predict the viscosity of multicomponent liquid n‐alkane and regular solutions. The modified Generalized Corresponding States Principel (MGCSP) reported by Wu and Asfour (1992), for only predicting the viscosities of n‐alkane mixtures, has been extended to predit the viscosities of multicomponent regular solutions. The predictive capabilities of several predictive models were analyzed. The obtained results showed that the pseudo‐binary McAllister model predicts the viscosity data better than the other existing predictive models.     

Pitting corrosion studies on Al and Al-Zn alloys in SCN solutions

Pitting of Al and Al-6%Zn and Al-12%Zn alloys in KSCN solutions was studied by means of potentiodynamic anodic polarization, cyclic voltammetry, potentiostatic and impedance techniques. Measurements were conducted under different experimental conditions, complemented by ex situ scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA). The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of Al₂O₃ on the anode surface (in case of Al) and the formation of ZnO on the Al₂O₃ matrix, in case of the two Al-Zn alloys (as evidenced from EDXA). The passive region is followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of SCN⁻ anions. SEM images confirmed the existence of pits on the electrode surface. Alloyed Zn was found to enhance pitting attack. The pitting potential (E_pit) decreases with an increase in SCN⁻ concentration and temperature, but increases with increasing potential scan rate. The current/time transients show that the incubation time for passivity breakdown decreases with increasing applied positive potential, SCN⁻ concentration, and temperature. Impedance measurements showed that Nyquist plots are characterized by a depressed charge-transfer semicircle, the diameter of which is a function of SCN⁻ concentration, applied potential, solution temperature and sample composition.     

Implications of standard states and ideal solution in terms of Raoult's law

Traditionally, Raoult's law has always been considered to describe the vapor-liquid equilibrium of ideal solutions. This treatment not only is awkward but also is not in complete agreement with the definition of an ideal solution in the sense of the Lewis-Randall rule. In this study, the characteristics of a model system of Raoult's law are analyzed. The analysis is based on the application of the Lewis-Randall rule in which the actual states of the pure components are used as the standard states. It is shown that, in the region where vapor-liquid equilibrium exists, neither the vapor nor the liquid is an ideal solution in the strict sense of the Lewis-Randall rule.     

Effect of Different Drying Methods on Rheological and Textural Properties of Balangu Seed Gum

The purpose of the present study was to investigate the effect of different drying methods on the rheological and textural properties and color changes in Balangu seed gum. Three drying methods, including air drying (40–80°C), freeze drying, and vacuum drying, were used. The apparent viscosity decreased from 0.161 to 0.056 Pa s with increasing temperature from 40 to 80°C (shear rate = 60 s^?1) and freeze-dried gum exhibited the highest viscosity among all dried gums (0.203 Pa s). Different time-independent rheological models (power law, Bingham, Herschel-Bulkley, Casson, and Vocadlo) were used to fit the experimental data and the results revealed that the Herschel-Bulkley model was the most suitable to describe the flow behavior of Balangu seed gum over the whole experimental range (r > 0.98). The hardness values of air dried Balangu seed gum gels varied from 33.1 to 40.4 g and were significantly lower compared to the freeze-dried and vacuum-dried gums (46.9 and 46.6, respectively). The consistency of samples decreased from 386.27 to 245.33 g · s when the drying air temperature increased from 40 to 80°C. The results indicated that the freeze-dried gum exhibited the highest hardness and consistency. The color of air-dried gum was darker (lower L* value) compared to the freeze- and vacuum-dried samples.     

Light-scattering studies on solutions of high and low molecular weight polystyrene mixtures used as models of microgel-containing solutions

Diluted solutions of linear polystyrene (PS) in toluene and dioxane were studied by the light-scattering method. The solutes were mixtures of high-M?_w and low M?_w PS. The dissolved PS mixtures were regarded as polymer solutions containing microgels, the high-M?_w PS being looked upon as the microgel counterpart. The calculation method as proposed by Strazielle¹ and Burchard² was used to evaluate the microgel percentage and particle size, whereby the method could be verified against mixtures with well-known weight composition and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document}. The \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values evaluated for the mixtures from the experimental data were compared with those estimated from the molecular weights of the components, their weight concentrations, and their \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values. The method^1,2 was found to be useful for evaluating the microgel content in a sample, but not for \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values as calculated by Guinier's procedure nor those calculated by Zimm's procedure; the former were low and the latter were even incongruous. A comparative analysis of the theoretical function P^?1(θ)-versus-sin² (θ/2) and experimental (Kc/R(θ))_c=0-versus-sin² (θ/2) curves allowed to discuss the effect of the course of these curves at samll angles from 0° to 30° on M?_w and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} as determined for the high and low molecular weight polystyrene mixtures in toluene as solvent.     

基于原位红外光谱技术的键合剂贮存老化规律及寿命研究

采用原位红外光谱技术开展键合剂在不同温度下的贮存老化规律及动力学研究,结果表明羟基为键合剂老化的薄弱环节.采用羟基官能团的变化规律进行动力学分析,得到活化能为117kJ/mol;以吸光度变化0.1％和1％作为贮存寿命的判据,键合剂在30 ℃下的贮存寿命分别为9.37 a和93.7 a.     

Comparison of color vision models based on spectral color representation

Recent break‐throughs in retinal imaging have raised new questions for color vision research, and the existing color vision models should be re‐evaluated. Many color vision models are based on an assumption that there are no differences in the detection phase, neither in the spatial configuration nor in the spectral sensitivities of cells. In this article, we have run experiments with four different color vision models. This evaluation gives us more knowledge about the essential properties of the models. We show how the tested color vision models are able to replicate the behaviour of human color vision by evaluating their performance in Farnsworth‐Munsell 100‐Hue color vision test. Also, the wavelength discrimination power of each model is presented and the properties of color spaces spanned by models are examined using samples from Munsell Book of Color. Our experiments show that there are large differences in the properties of different models. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 341–350, 2009     

聚酰胺酸纺丝溶液的流变性能研究

由均苯四酸二酐(PMDA)和4,4'-二氨基二苯醚(ODA)在N,N-二甲基乙酰胺(DMAc)中共聚合制得聚酰亚胺前驱体——聚酰胺酸的纺丝溶液,采用哈克流变仪研究了溶液的流变性能。结果表明:聚酰胺酸溶液属于切力变稀的非牛顿流体;溶液的表观黏度随溶液温度的升高而降低,随溶液浓度的升高或聚合物特性黏度的增大而增大。溶液温度的升高、浓度的降低或聚合物特性黏度的减小均使得聚酰胺酸溶液呈现切力变稀行为的临界剪切速率变大,使得溶液的非牛顿指数增大,同时使得溶液的结构黏度指数减小。溶液的黏流活化能随剪切速率的增加或随溶液浓度的增高而下降。