聚合物表面与材料的耐候性

聚合物材料的表面与环境直接接触,从而成为高分子材料大气老化与抗老化的焦点。本文较系统地论述了大气环境对聚合物表面的作用;在研究聚合物表面老化现象和机理中现代测试技术的应用状况;以及强化聚合物表面对提高聚合物材料耐候性的重要意义。     

聚乙烯—丙烯酸辐射接枝物形态结构及性能的研究

采用红外光谱，扫描电镜Ｘ光衍射和差热技术研究了聚乙烯－丙烯酸辐射接枝物的形态结构，并测定其性能，结果表明，接枝反应是由聚乙烯表面向内部进行并达到整体接枝，两种聚合物间存在相结合，随着接枝率的提高，材料的凝胶含量，亲水性，电性能和机械性能相应提高。     

材料信息

材料信息能降低发动机磨损的含氟聚合物涂层美国韦特福特（Ｗｈｉｔｆｏｒｄ）公司研制了一种含氟聚合物涂层可以降低汽车发动机中活塞与汽缸壁、轴颈与轴衬等摩擦表面的磨损。这种称为“Ｘｙｌａｎ”的涂层由一种含氟聚合物基体和聚四氟乙烯润滑料组成。可在－２５０到２...     

聚合物材料表面原子氧防护技术的研究进展

聚合物材料具有质量轻、强度高等优点, 常被用作航天器表面的复合结构基材。原子氧是低地球轨道空间中成分含量最高的粒子之一, 对暴露在航天器表面的聚合物材料易形成大通量、高能量轰击, 造成其表面氧化侵蚀和质量损失, 使聚合物材料的性能发生不同程度的衰退, 也是导致航天器件可靠性降低、工作寿命缩短的主要环境因素。本文对当前国内外通用的几种聚合物材料表面原子氧防护技术进行了整理归纳, 其中表面化学改性方法结合了体材改性和常用防护涂层的优点, 得到的有机/无机复合改性防护层具有较好的综合防护性能。文中分析了近年来由计算模拟法开展原子氧与表面防护材料相关作用机理的研究, 指出采用计算模拟结合试验的研究方法, 有可能从本质上揭示复合改性层与原子氧的作用机理, 从而促进原子氧防护材料与防护技术的研究发展。     

高能离子辐射法制备表面超硬聚合物

高能离子辐射法制备表面超硬聚合物众所周知，有机聚合物材料自身软且易磨损，硬度及抗磨性等方面无法与不锈钢等合金相比。然而，美国田纳西州的橡树岭国家实验室（ＯＲＮＬ）近年来研究的制备工艺，能使聚合物表面硬度比钢强许多倍，同时抗磨与抗腐蚀性比钢更强。该工艺...     

离子注入对聚合物材料表面改性的研究与应用进展

离子注入对聚合物材料表面改性有着独特的优越性,文中介绍离子注入技术在聚合物材料表面的力学性能、电学性能、光学性能、生物相容性能等方面改性的最新研究与应用进展。     

聚合物低温等离子体表面双疏改性的研究现状

疏水疏油的聚合物材料广泛地应用于国防、工农业生产和日常生活,含氟低温等离子体对聚合物表面双疏改性的研究得到关注。文中总结了以降低聚合物表面能和改变表面粗糙度两方面来提高表面双疏性能的基本原理及相应的实验研究状况,阐明了含氟低温等离子体处理技术能在降低表面能的基础上改变聚合物表面粗糙度,是提高聚合物材料表面双疏性能的有效途径。最后,结合等离子体科学与技术的国内外发展情况,提出表面双疏理论需要进一步发展和完善的方面,展望我国在服装面料等离子体表面双疏改性的自主产业化及其它应用领域的发展前景。     

可直接还原银纳米粒子的儿茶酚基聚合物膜的制备及抗菌性能研究

将预先合成的聚合物PVA-DOPA与PVA共混制备聚合物膜PVA/PVA-DOPA;由于含儿茶酚基的3,4-二羟基苯丙氨酸(DOPA)具有氧化还原活性,可直接利用PVA/PVA-DOPA聚合物还原银纳米粒子并使其负载在PVA/PVA-DOPA膜表面。紫外可见光谱表明,PVA-DOPA与Ag+作用时,发生氧化还原反应,酚羟基被氧化成醌,在415nm处出现特征吸收峰。通过扫描电子显微镜和透射电子显微镜,可观察到聚合物膜表面Ag纳米粒子的形态;并通过热失重分析计算出PVA/PVA-DOPA/Ag0膜中Ag的负载量。抗菌性研究测试表明制得的聚合物膜具有良好的抗菌性。因而,PVA/PVA-DOPA聚合物膜可用作抗菌性包装材料、涂层材料和生物医用材料等多种功能材料。     

离子注入聚合物表面改性的研究

离子注入聚合物材料表面改性有着独特的优越性。综述了离子注入技术对聚合物表面的机械性能、电学性能、光学性能和磁学性能等方面改性的最新研究与应用进展。     

垂直轮廓剖面迹线法测定聚合物材料断面粗糙度的研究

运用垂直轮廓剖面迹线法测定了聚合物材料的断面轮廓线粗糙度参数ＲＬ及聚合物材料冲击强度和断口表面粗糙度参数Ｒｓ的关系。实验结果指出：聚合物的面轮廓线粗糙度与试样形状、断裂性质及断口形貌等因素有关。缺口试样断口形貌均衡分布时，试样两表面的测量值相等；断试样表面和心部测量结果相同；韧断试样表面测量结果大于心部测量结果。无缺口试样冲击脆断时，试样表面测量结果与断裂源位置有关，心部测量结果一般大于两表测量平     

The X-HPD—conceptual study of a large spherical hybrid photodetector

We present the results of a conceptual study demonstrating the feasibility of a large spherical hybrid photodetector with central anode. A prototype tube with 208 mm diameter and an anode in form of a metallic cube has been fabricated. In the final version of the so-called X-HPD concept the anode will be a scintillator cube with plated faces and a small photodetector to readout the bottom. The bialkali photocathode covers three quarters of the sphere surface. Combined use of this cathode in transmissive and reflective mode leads to effective quantum efficiency values exceeding those obtained in conventional hemispherical PMT designs. Further features of the concept are a photoelectron collection efficiency approaching 100% and a photon amplification in the scintillator crystal leading to a distinct single photoelectron signal.

Using a custom built electron accelerator based on a CsI transmissive photocathode, LSO and YAP block crystals in geometries adapted to the anode of an X-HPD have been tested with single photoelectrons in the 10–30 keV energy range. The scintillation light was readout with a conventional PMT or a Si-PM. More than 30 photoelectrons per incident electron could be detected with the PMT.     

Experimental pure fluid and binary mixture performance in a heat pump equipped with a distillation column

An experimental heat pump system that included a distillation column, accumulator/sump, and heater was experimentally investigated using two different working fluids, R32 and a mixture of R32/134a. Performance variations with changes in sump heater power, condenser and evaporator heat transfer fluid flow, and compressor speed were examined. Heating capacity generally increased with increases in the factors tested. Heating capacity increases were generally smaller with the R32/134a tests than with the R32 tests, except with variations in sump heater power. An increase in sump heater power caused a pronounced increase in the circulating R32 concentration during the mixture tests, and the heating capacity increased markedly. The increase in heating capacity with sump heater power during the R32/134a tests was on par with the increase with compressor power during these same tests. The increase in capacity with sump heater power during the R32/134a tests also was substantial even when compared with the capacity increase with compressor speed during the R32 tests.     

The effect of martensite volume fraction and particle size on the tensile properties of a surface-carburized AISI 8620 steel with a dual-phase core microstructure

This study is focused on the production of a dual-phase steel structure in the core of a surface-carburized AISI 8620 cementation steel and the effect of martensite volume fraction (MVF) and martensite particle size (MPS) on tensile properties. Experimental results showed that, compared with specimens with a fully martensitic microstructure in the core, those with a dual-phase microstructure in the core exhibited slightly lower tensile and yield strength but superior ductility without sacrificing surface hardness. In specimens with a dual-phase microstructure in the core, the tensile strength increased and ductility decreased with increasing MVF. Both the tensile strength and the ductility increased with decreasing MPS at constant MVF. The best combination of tensile strength and ductility was obtained with a fine MPS at a constant MVF of 25%.     

Statistical Analysis of Macromolecular Chains in the Space Filled by Nanoparticles

The paper presents a combination of worm-like chain numerical models and one with a finite set of nano-particles. The primary objective of the models was to analyze the distribution of space in a system filled by particles. Information on the distribution of space was compared to properties of chains inside the set of particles. The set of nanoparticles was constructed with a tool generating a finite set of particles that is randomly distributed in a given space. The particles have a prescribed volume fraction and uniform size. First, the proportions of chains and particles were compared. The length of chain was expressed in terms of end-to-end length. It was then compared to the size of gaps between two particles. The volume of chain was compared to the volume of space delimited by the particles. Next, a set of 10,000 random chains was generated and these were introduced into the particle set. The contact of a chain with the surface of a particle resulted in the special structural elements of the chain: a chain connecting two different particles, a loop which begins and ends at the same particle, a part of a chain which is completely adhered to the particle surface, a chain attached to a particle with one free end, as well as completely free chains. The chains were classified under three classes: chains which were not in contact with particles, chains which were in contact with one particle, and chains which were in contact with two or more particles. A statistical representation of each class is presented. The contact between chain and particle can influence macroscopic properties such as those that are elastic.     

Numerical Simulations of Convection Induced by Korteweg Stresses in a Miscible Polymer–Monomer System: Effects of Variable Transport Coefficients, Polymerization Rate and Volume Changes

We modeled a miscible polymer-monomer system with a sharp transition zone separating the two fluids to determine if convection analogous to Marangoni convection in immiscible fluids could occur because of thermal and concentration gradients. We considered three cases: with a temperature gradient along the transition zone, with a variable transition zone width, and one with a gradient in the conversion of polymerization. Using the Navier–Stokes equations with an additional term, the Korteweg stress term arising from non-local interactions in the fluid, we demonstrated with realistic parameters that measurable fluid flow would result in the absence of buoyancy-driven convection for all three cases. We show that even if the Korteweg stress is not a function of temperature, the increase in the diffusion coefficient with temperature can result in convection because a gradient in the transition zone width develops. We also examine the effects of a polymer viscosity that is not only a function of concentration but also temperature. We demonstrate that a constant flux of heat, as would be realistic for a heating element in contact with the side of the reactor, would produce a greater flow than a linear thermal gradient parallel to the transition zone. We demonstrate that qualitatively different flow patterns can be realized by using unusual initial conditions that could be realized with different masks for the photopolymerization. We also demonstrate that the volume change during polymerization and caused by side heating could not cause significant fluid flow that would confound the observation of Korteweg-stress induced flows. To avoid buoyancy-driven convection, the experiment would have to be performed in microgravity.     

Hyperphosphatemia among end‐stage renal disease patients in developing countries: A forgotten issue?

The prevalence of hyperphosphatemia and increased calcium-phosphorus product has never been evaluated in a large multicenter study in a developing country. Our aim is to study the prevalence of hyperphosphatemia in 38 HD centers in Egypt (as an example of a developing country) and to correlate it with different co-morbid conditions and the patient's demographic data. This is a cross-sectional study conducted on 1005 chronic kidney disease stage 5 patients (CKD-stage 5) on HD for a period of more than 1 year in 38 dialysis centers in Egypt. All patients were receiving calcium-based salts as a phosphate binder. Hyperphosphatemia and increased calcium-phosphorus product were evaluated and correlated with different parameters including age, sex, knowledge by diet parameters, HD session duration, the frequency of HD per week, the type of dialysis membrane, the surface area of the dialyzer, dialyzer phosphorus clearance (phosphorus KoA), and the type of dialysate. Other co-morbid medical conditions and evidence of IHD were also investigated. Hyperphosphatemia was present in 69.1% of cases and a high calcium-phosphorus product was present in 30.2%. A higher calcium-phosphorus product was found among males. 83.2% of those with a poor knowledge by diet parameters had hyperphosphatemia compared with 67.6% in patients with a satisfactory knowledge by diet parameters. 72.3% of patients using a membrane with low-to-medium clearance had hyperphosphatemia, compared with 67.2% using a membrane with a high clearance. Seventy-two percent of patients with IHD were hyperphosphatemic compared with 67.6% of the non-ischemic patients. Hyperphosphatemia is a major problem in dialysis patients in developing countries, reflecting differences from developed countries regarding dietary habits, ethnic factors, dialysis quality, types of dialysis membranes, as well as economic factors hampering the use of the more expensive phosphate binders. Extended dialysis hours may be a good alternative solution in developing countries.     

基于SPH方法的低韦伯数下三维液滴碰撞聚合与反弹数值模拟研究

光滑粒子流体动力学方法（SPH方法）作为纯拉格朗日粒子方法,可以有效避免网格法在模拟大变形过程中带来的网格扭曲等缺陷,适合模拟含大变形的液滴碰撞聚合与反弹过程。该文基于Ott和Schnetter提出的修正SPH方法,利用有限差分与SPH一阶导数相结合的方法处理粘性项中的二阶导数问题,进行Couette流算例验证,数值解...     

一种可稳定计算负跃层浅海环境下声场的波数积分方法

提出了一种可以稳定计算负跃层浅海环境中声场的波数积分方法,通过对艾里(Airy)函数的归一化,得到了声源位于水体不同层中的系数矩阵,该系数矩阵是无条件稳定的。结合仿真实例,将该方法的计算结果与Airy函数未作归一化得到的计算结果进行比较,结果显示,当Airy函数未作归一化时,在某些情况下不能保证深度格林函数的足够收敛性,而该方法可以很好地解决该问题。同时将该方法的计算结果与简正波模型KRAKENC的计算结果进行对比,结果表明,文中提出的数值计算模型可以作为负跃层浅海环境中声场计算的有效补充。     

聚碳硅烷的挤出胀大与Y型SiC纤维的异形度

研究了聚碳硅烷(PCS)熔体在Y型喷丝孔中的挤出胀大机理、膨胀模型以及膨胀比对Y型碳化硅纤维异形度的影响.结果表明:采用圆形喷丝孔时PCS的膨胀比为1.02～1.15,Y型喷丝孔时膨胀比为1.02～1.43,在与圆形喷丝孔成形条件相当的情况下,Y型喷丝孔的膨胀比比圆形孔的高出约15%,Y型口模周边的剪切应力分布不均、剪切应力内外差异和区域差异是造成其膨胀比增大的根本原因.PCS熔体温度降低或软化点提高,其出口挤出胀大效应增大.由于模口膨胀的影响,Y型PCS纤维的异形度比喷丝孔异形度下降10%～20%.     

Variations in dynamic vehicle load on road pavement

This study proposes a spectral approach to the evaluation of variations in dynamic vehicle load on road pavement associated with a vehicle moving at constant speed along a road with a rough surface. The influence of vehicle speed and road roughness on variations in dynamic vehicle load was investigated. The results show that the standard deviation of dynamic vehicle load increases twofold, with a fourfold increase in the road roughness coefficient, and increases approximately linearly with the increase in vehicle speed.