塑料挤出吹塑的机理问题

挤出吹塑过程由型坯成型，型坯吹胀与制品冷却三个阶段构成。采用不同的方法对该三阶段的机理问题进行了研究。采用神经网络方法预测了受模口温度和挤出流率影响的型坯成型阶段的膨胀，利用建立起来的神经网络模型预示的膨胀与实验结果很吻合，且可在一定范围内，预示不同工艺条件下型坯的直径膨胀和壁厚膨胀。为型坯的直径和壁厚的在线控制提供了理论依据。基于薄膜近似和noe-Hookean本构关系。建立了描述型坯自由吹胀的数学模型，并通过实验方法获得了型坯吹胀的瞬态图象，比较发现，理论预示的型坯轮廊分布与实验观察结果较吻合，该模型还可预示型坯的自由吹胀对材料性能，型坯尺寸和工艺条件等的依赖性，基于ANSYS有限元软件，对吹塑制品的三维冷却进行了模拟，预示了制品厚度方向任一位置的瞬态温度分布，并可预示成型工艺参数，制品壁厚，塑料与模具材料的热性能以及吹塑模具冷却的强度与时间等对吹塑制品冷却的影响，这可为进一步分析吹塑制品的显微结构和性能提供温度数据。     

多熔体多次注塑成型沿流动方向上微观结构演变探究

不同于传统注射成型,多熔体多次注塑成型(M³IM)过程中存在特殊的二次流动场和温度场,导致其试样的形态结构与演变规律更加复杂.本文采用实验与模拟相结合的方法,详细探究了熔体沿流动方向上二次流动过程中剪切场和温度场的分布,及其对试样形态结构的影响.结果发现,一次注射聚偏氟乙烯(PVDF)熔体是由一次流动层和二次流动层两部分所构成,且在一次流动层末端形成熔体突破区.此外,剪切场和温度场在熔体突破区前段、中段和后段存在显著差异,导致试样微观结构沿流动方向呈多级分布,即在突破区前段PVDF形成取向结构,而在突破区段PVDF受到强的二次剪切作用,形成了大量β晶和取向结构.与此不同,在突破区后段,PVDF则主要受到二次剪切生热作用的影响,形成了具有较高熔点(～190℃)的特殊“亮带”结构.     

层状共连续PA6/SEBS体系的结晶取向及其低膨胀化机理研究

研究了注射成型尼龙6/苯乙烯-乙烯/丁烯-苯乙烯嵌段共聚物(PA6/SEBS)体系中微结构形态,SEBS含量,PA6结晶取向对线膨胀系数(CLTE)的影响.研究表明,当SEBS含量超过20wt%,PA6/SEBS注射成型体系形成层状共连续结构时,可以明显地降低流动方向的热膨胀系数.TEM和WAXD分析表明,该层状共连续结构中不仅SEBS微层取向,而且大多数PA6片晶垂直于SEBS微层生长,其中晶胞b轴(PA6分子链)倾向于沿流动方向取向.程序升温WAXD研究表明,PA6/SEBS(60/40)体系中各晶轴的线膨胀系数差别很大,其中晶胞b轴为-5.8×10-5K-1.具有负膨胀系数的晶胞b轴沿着流动方向取向可能是除层状共连续结构效应以外导致材料低膨胀化的第二种驱动力.     

半结晶聚合物注射成型中结晶动力学的数值模拟

对半结晶聚合物注射成型过程及其结晶过程进行偶合模拟,分析了二者的相互影响.具体是在注射成型数值模拟中考虑结晶动力学效应,分别在本构方程、能量方程及材料物性参数方程中引入反映结晶效应的参数;同时在结晶动力学计算中考虑流动诱导效应,从能量的角度提出并使用修正的动力学模型,用材料流动过程的耗散能表征流动对结晶的影响.通过对等规聚丙烯(iPP)和聚对苯二甲酸乙二醇酯(PET)两种半结晶聚合物注射过程模拟结果的分析比较,证实成型过程具有加速结晶的作用.同时,材料的结晶也对注射成型加工过程,尤其是保压与冷却过程的温度场分布有较大的影响.     

气辅注塑CAE模拟技术的理论基础及分析实例

阐述了CAE模拟技术在气体辅助注射成型模具设计过程中的重要意义；介绍了气体辅助注射成型充填流动分析及保压分析中塑料熔体所遵循的数学模型和粘度参数模型，并介绍了在粘性流体力学基础上对数学模型进行了合理的简化和假设的方法；运用CAE软件C—MOLD对汽车保险杠模具结构设计及成型工艺条件进行了气辅注射成型模拟分析，优化了气体充填成型工艺和充填效果，改善了制品表面质量和力学性能，提高了首试成功率。     

气流床煤气化炉内流动、混合与反应过程的研究进展

气流床气化过程涉及高温高压下湍流多相流动与复杂化学反应过程的相互作用,涵盖喷嘴雾化与弥散、复杂多相射流流动、炉内湍流混合、复杂气化反应、火焰结构及温度分布等诸多方面,是世界各国研究的热点.对近年来世界各国在气流床气化过程研究上取得的进展进行了综述,包括喷嘴雾化与颗粒弥散机理与雾化过程的影响因素、撞击流驻点偏移规律和撞击面振荡规律、撞击火焰结构与炉内三维温度场、典型煤种气化反应特性与石油焦气化特性以及气流床气化过程模拟.对气流床气化过程未来的研究重点进行了展望.     

热、力及其复合外场原位辅助熔融沉积成型技术研究进展

熔融沉积成型(fused filament fabrication, FFF)是典型的聚合物增材制造技术之一,因其原料利用率高,成型原理简单且成本低而受到广泛关注。然而,FFF技术采用逐层堆积的加工方式,导致其成型件的层间界面结合强度较弱、宏观力学性能呈各向异性,因此较少用于工业领域关键零部件的制造。为此,发展了外场原位辅助的FFF技术,借助热场、力场及其复合外场,原位促进FFF成型过程中的层间结合行为,进而提高FFF成型件的宏观力学性能。本文从FFF成型的层间结合现象出发,归纳无定形聚合物和结晶性聚合物的层间结合机理,概述热场和力场对层间结合的影响机制,综述各类热、力及其复合外场辅助FFF技术的研究进展,并讨论各类原位辅助技术对FFF成型件力学性能的改善与不足,最后展望该技术在材料、工艺与装置等方面的发展前景和趋势,为促进FFF技术的工程应用提供理论支撑和技术参考。     

用模压成型方法制备HDDR粘结NdFeB磁体的成型性研究

在形状复杂或大尺寸的模压成型粘结磁体制备过程中，由于粉末颗粒间以及磁粉与模壁间的摩擦，造成沿压制方向的压制压力递减，使得磁体密度的不均匀分布的现象，成为不可避免，为了改善磁体密度分布不均匀的现象，本研究选取用HDDR NdFeB磁粉模压成型制备的薄壁环作为研究对象，系统地研究了润滑剂的添加量以及润滑剂和增强剂的添加方式对磁体密度、密度分布的均匀性以及磁体抗压强度的影响，通过复合添加润滑剂和增强剂的方法，可以保证在磁体抗压强度不降低的前提下，提高磁体的密度，改善密度分布的均匀性，从而改善粘结磁体的成型性。     

EVA流动改进剂的分子量及分子量分布对大庆原油流变性的影响

研究了两类醋酸乙烯酯（ＶＡ）含量不同的乙烯－醋酸乙烯酯共聚物（ＥＶＡ）流动改进剂的分子量（Ｍｎ：１０３００～２５８０Ｎ和分子量分布（ｄ：１．４５～３．９）对大庆高蜡原油低温流动行为的影响。实验结果表明，在８０克原油中含有２００ＰＰｍ分子量或分子量分布不同的各种ＥＶＡ流动改进剂都不同程度改善了大庆原油的低温流变性。当改进剂分子量分布相近时，改进剂的改进效果存在某一最佳分子量；当改进剂分子量相近并处于最佳分子量范围内时，则窄分布改进剂的效果比宽分布的改进剂为佳。反之，以宽分布改进剂为宜。     

聚合物流动诱导结晶研究进展

在外力作用下,半结晶聚合物的结晶形态、结晶动力学等与静态条件下相比,均发生了较大的变化,并继而影响到成型制品的性能.自上世纪六十年代人们从溶液中发现外力诱导结晶现象以来,相继开展了大量相关的理论和实验研究,提出了一些模型,随着测试手段的改进,流动诱导结晶研究取得了较大的进展,但仍存在许多争议.本文回顾了围绕聚合物流动诱导结晶所开展的工作,重点综述了流动诱导结晶形态变化、分子量及其分布、剪切速率、温度等因素对聚合物结晶动力学的影响,并指出了今后的研究方向.     

The Hofmeister anion effect and the growth of polyelectrolyte multilayers

The influence of a variety of counteranions on the properties of polyelectrolyte multilayers deposited by layer-by-layer technique is studied by using ellipsometry and AFM. We found out that in thin dry multilayers (20-90 nm) ofpoly(4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium) (PDADMA), the thickness follows reasonably well the position of the counteranion in the Hofmeister series. The polyelectrolyte-counteranion interaction is studied by means of viscosity measurements of semidilute solutions of PDADMA in the presence of different anions. The dynamic viscosities follow the Hofmeister series of anions and correlate with the thickness of multilayers. Two parameters describing the interaction of ions with water, the Jones-Dole viscosity B coefficient and the hydration entropy, are used to explain the anion effect on the developing multilayer thickness. Reasonably smooth and monotonic functional dependence is observed between the layer thickness and these two parameters.     

Adsorption studies of polyethers Part II: adsorption onto hydrophilic surfaces

The adsorption of BAB-type triblock copolymers (B=poly(ethylene oxide); A=poly(propylene oxide)) from aqueous solution onto hydrophilic silica particles is described with particular reference to the role of the copolymer composition. The adsorbed amount and the layer thickness were determined by the standard depletion method and photon correlation spectroscopy, respectively. Snowtex-YL silica was used as the adsorbent. The results show an increase in the adsorbed amount with increasing molar masses of both PEO and PPO blocks. The adsorbed layer thickness is found to depend strongly on PEO block mass. Both these parameters (adsorbed amount and hydrodynamic layer thickness) show a maximum as a function of the mole fraction of the PPO block present in the copolymer. The conformation of the adsorbed layer is determined by the surface–copolymer interaction; principally by the interaction of the hydrophilic PEO block with the silica surface. A good qualitative agreement of the experimental results with theoretical predictions and self-consistent mean field calculations has been found.     

Depth distribution of multiple order X-ray scatter

Scatter can significantly affect quality of projectional X-ray radiographs and tomographic reconstructions. With this in mind, we examined some of the physical properties of multiple orders of scatter of X-ray photons traversing through a layer of scattering media such as water. Using Monte Carlo techniques, we investigated depth distributions of interactions between incident X-ray photons and water before the resulting scattered photons reach the detector plane. Effects of factors such as radiation field size, air gap, thickness of the layer of scattering medium and X-ray energy, on the scatter were included in the scope of this study. The following scatter characteristics were observed: (1) for a layer of scattering material corresponding to the typical subject thickness in medical imaging, frequency distribution of locations of the last scattering interaction increases approximately exponentially with depth, and the higher the order of scatter or the energy of the incident photon, the narrower is the distribution; (2) for the second order scatter, the distribution of locations of the first interaction is more uniform than that of the last interaction and is dependent on the energy of the primary photons. Theoretical proofs for some of these properties are given. These properties are important to better understanding of effects of scatter on the radiographic and tomographic imaging process and to developing effective methods for scatter correction.     

Mathematical modeling of biosensor action in the region between diffusion and kinetic modes

We describe the action of electrochemical enzyme-based biosensor by applying mathematical modeling. We consider two types of biosensors: a biosensor containing a single heterogeneous enzyme layer and biosensor containing an additional protecting polymer-based layer. The initial parameters of the biosensor were selected on the basis of typical immobilized glucose oxidase-based electrochemical biosensor. A phenomenon of the accumulation of the electrochemically active product inside the biocatalytic layer was evaluated. It was shown that accumulation of the product can increase sensitivity of the biosensor no more than 2.6 times. Due to the asymmetric distribution of the electrochemically active product inside the enzyme-containing membrane and asymmetric diffusion of the substrate, it was shown that the thickness of the membrane possesses an optimal value. For the selected set of initial parameters, the optimal thickness of the enzyme-containing layer was 2.9–4.5  $\upmu $ m. Real profiles of the impact of the thickness of the membranes were evaluated. A method for the evaluation of acceptable fluctuations of the membrane diffusion parameters on biosensor response was created, and the profiles of the dependence were calculated. These dependencies can be used for development of the software for biosensor monitoring.     

Ion penetration into an ‘unfriendly medium’ and the double layer capacitance of the interface between two immiscible electrolytes

We develop a theory of the double layer at electrolyte | electrolyte interfaces with account for the finite thickness of the interfacial region. This includes the distribution of ions between the two phases and smooth variation of dielectric properties across the interface. The theory offers simple laws for the dependence of the double layer capacitance on the nature of ions, ionic concentrations and potential, which are in line with experimental observations. The theory shows which parameters reflect the nature of ions and the structure of the interface, and how these parameters can be extracted from the capacitance data.     

A statistical study of the kinetics of phase separation for a liquid crystalline mixture

The kinetics of cholesteric phase growth during the phase separation of an isotropic liquid crystalline mixture was studied by polarizing optical microscopy within the framework of the thermodynamics of irreversible processes. The rules governing time-dependent changes in the parameters of the statistical droplet size distribution of the cholesteric phase were determined. The influence of the thickness of the liquid crystalline mixture layer on the size of the droplets formed was studied.     

Synthesis and diffusion permeability of MF-4SK/polyaniline composite membranes with controlled thickness of the modified layer

A new method is proposed for the synthesis of anisotropic membranes based on F-4SF films, which ensures their modification with polyaniline in a layer with a fixed thickness. The concentration dependences of conductivity and diffusion permeability of the composite membranes are studied. These parameters decrease with increasing thickness of the polyaniline-modified layer. The quantitative correlation is revealed between the regularities of variations in both transport characteristics and the thickness of the modified layer. The absence of the asymmetry of the diffusion permeability of the examined composite membranes is explained in terms of the model of a charged bilayer membrane.     

Formation of multilayered structures in the layer by layer deposition of colloid particles

Theoretical calculations of particle film formation in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to twenty) was simulated for two kinds of particles of equal size. The interaction of two particles of different kind resulted in irreversible and localized adsorption upon contact, whereas particles of the same kind were assumed to interact via the hard potential (no adsorption possible). Using this algorithm particle coverage (2D density) and volume fraction (3D density) were calculated as well as the film thickness as a function of the number of layers. Additionally, the structure of the film was quantitatively characterized in terms of the 2D and 3D pair correlation functions. The simulations revealed that particle concentration distribution in the film was more uniform for low precursor layer density than for higher density, where well-defined layers of closely packed particles appeared. It was also predicted theoretically that the averaged value of particle volume fraction in the uniform film region was rho(LbL)=0.42, which is very close to the maximum packing density equal to 0.382 predicted from the 3D RSA model. On the other hand, the roughness of the film was the lowest at the highest precursor layer density. It was shown that for low precursor layer density the film thickness increased with the number of layers in a nonlinear way. However, for high precursor layer density, the film thickness increased linearly with the number of layers and the average layer thickness was close to the hexagonal layer thickness equal to 1.73a p. It was concluded that our theoretical results can be effectively exploited for interpretation of the LbL processes involving colloid particles and polyelectrolytes.     

二价金属离子对含铜水滑石结构稳定性的影响

通过构建不同的二价金属离子(M²⁺=Mg²⁺, Ca²⁺, Zn²⁺, Cd²⁺, Ni²⁺, Co²⁺)部分取代铜离子形成CuM₂Al 水滑石(CuM₂Al-LDHs)的周期性模型, 基于密度泛函理论(DFT), 用CASTEP程序模块对周期性模型进行几何全优化和性质计算, 通过分析各体系的结构参数、电子排布、Mulliken 电荷布居、氢键、结合能, 总结出含铜水滑石体系结构的稳定性规律. 计算结果表明: 在CuM₂Al-LDHs 体系中, 主客体间作用力对层板厚度的影响占主要因素; M离子对中心三价铝离子的影响较小, 对二价铜离子的影响较大, 其中价电子均匀排布的M离子对铜的畸变影响小于价电子不均匀排布的M离子. 另外在价电子均匀排布的CuM₂Al-LDHs 体系中, 主客体间的静电作用力和氢键强度逐渐增强. 总体上, 随着M离子周期数的增加, 体系的畸变角增大, 结合能绝对值逐渐减小, 体系的稳定性下降. 价电子不均匀排布的CuCo₂Al-LDHs 体系的稳定性最差. 这有助于从理论上更好地认识含铜水滑石的合成规律.     

Residence time distribution for electrokinetic flow through a microchannel comprising a bundle of cylinders

The electrokinetic flow of an electrolyte solution through a microchannel that comprises a bundle of cylinders is investigated for the case of constant surface potential. The system under consideration is simulated by a unit cell model, and analytical expressions for the flow field and the corresponding residence time distribution under various conditions are derived. These results are readily applicable to the assessment of the performance of a microreactor such as that which comprises a bundle of optical fibers. Numerical simulations are conducted to investigate the influences of the key parameters, including the thickness of the double layer, the strength of the applied electric field, the magnitude of the applied pressure gradient, and the characteristic sizes of a microchannel, on the residence time distribution. We show that the following could result in a shorter residence time: thin double layer, strong applied electric field, large applied pressure gradient, and small number of cylinders. Based on the thickness of the double layer, criteria are proposed for whether the flow field can be treated as a laminar flow or as a plug flow, two basic limiting cases in reactor design.