聚合物共混相容性分子动力学模拟进展

本文简要介绍了分子模拟方法和分子动力学方法.着重从分子动力学模拟角度介绍如何模拟聚合物共混相容性的方法,引入了溶解度参数和Huggins-Flory相互作用参数的概念以及分子动力学模拟的具体方法.文章综述了分子动力学模拟在研究聚合物共混相容性的国内外的现状及应用;并对分子动力学模拟的发展趋势作了展望.     

PVD薄膜生长的Monte Carlo模拟

蒙特卡罗(Monte Carlo,MC)和分子动力学是模拟薄膜生长的两种基本方法.本文结合各种PVD技术的工艺特点,介绍了薄膜生长的Monte Carlo模拟.详尽地总结了载能粒子沉积薄膜生长的Kinetic Monte Carlo模型和算法.最后指出建立精细的模型、算法并适当应用分子动力学是提高模拟可靠性的方法.     

聚乳酸玻璃化转变行为的分子模拟

采用等温等压(NPT)正则系综,用分子动力学方法研究了聚乳酸的玻璃化转变行为,获得了玻璃化转变温度.在230～440K范围内,通过模拟体系的密度、比体积及相关径向分布函数等参数,最终确定了聚乳酸的玻璃化温度,模拟计算的结果与实验值吻合.     

分子动力学模拟及其在材料科学中的应用

综述了分子动力学模拟技术的发展,介绍了分子动力学的分类、基本原理、原子间势函数的发展及势参数的确定、相关有限差分算法、初始条件和边界条件的选取、平衡系综及其控制、感兴趣量的提取以及分子动力学模拟在材料科学中的一些应用.     

氧气在PDMS中扩散的分子动力学模拟

分子动力学方法模拟了300K时氧气分子在聚合物PDMS中扩散的情况,讨论模拟时间和聚合度对模拟结果的影响,发现模拟时间太少对模拟结果不利,应以大于1000ps为宜,聚合度一定范围内也可以影响氧气在PDMS内的扩散,还讨论自由体积对扩散的影响,与自由体积理论取得统一。     

材料摩擦磨损分子动力学模拟的研究进展

随着新技术的发展以及材料服役环境的日益复杂化,传统的试验研究已经不能满足人们对摩擦磨损的认识需求,因此必须借助数值模拟方法来研究材料的摩擦磨损行为.特别是随着近年来原子尺度理论模型的不断完善和计算机运算能力的不断提高,分子动力学模拟已经成为研究材料摩擦磨损行为和机制的重要方法.本文详细综述了材料摩擦磨损分子动力学模拟的国内外研究现状.首先阐述了分子动力学模拟中势能函数的建立;其次介绍了材料摩擦磨损分子动力学模拟常用的接触模型;然后概述了采用分子动力学模拟方法研究接触面积、载荷、温度、速度和晶体取向等因素对材料摩擦磨损的影响;最后指出了目前材料摩擦磨损分子动力学模拟中存在的一些问题,并对未来发展方向进行了展望.     

杜仲胶/天然橡胶共混物的分子动力学模拟和耗散粒子动力学模拟

应用分子动力学(MD)和耗散粒子动力学(DPD)模拟方法对杜仲胶(TPI)、天然橡胶(NR)的相容性进行了研究。采用MD模拟方法,在COMPASS力场下,对纯物质在不同聚合度下的溶度参数、一系列共混比的TPI/NR共混物内聚能密度、Flory-Huggins作用参数进行了模拟计算,确定了纯物质单链的聚合度,经判断各比例共混物的相容性均较好;采用DPD模拟方法对TPI/NR共混体系的相结构进行了研究,从等密度图可以进一步判断共混体系的相容性;分析比较两种纯物质的径向分布函数,揭示了其相互作用的本质;经过分析比较静态力学性能,发现共混比为1/3的TPI/NR共混物性能最佳,其结论与实验结果一致。     

MgO材料高压熔化特性的分子动力学模拟

用Shell模型分子动力学(MD)方法对MgO材料的高压熔化特性进行了研究,势函数取Buckingham形式.将计算得到的熔化曲线与实验以及其它理论结果在0～140GPa的压力范围内做了比较,通过修正得到的MgO熔化温度和实验测量能够很好地符合.MgO熔化模拟的结果对固体材料一阶相变分子动力学模拟的过热理论做了进一步的验证.另外,我们对反映体系微观结构的MgO径向分布函数(RDF)进行了分析.     

分子动力学模拟在塑料材料中迁移研究现状

目的概述分子动力学模拟方法应用于小分子物质在食品塑料包装材料中迁移研究的应用进展。方法综合近20年国内外分子动力学模拟方法在小分子扩散行为的研究进展。结果采用分子动力学模拟方法不仅可以定性地描述小分子在食品塑料包装材料中的扩散行为,而且能模拟聚合物材料的一些结构与性能,分析影响小分子迁移行为的因素,确定小分子的扩散系数。结论分子动力学模拟方法在食品塑料包装材料迁移研究应用中仍存在许多尚未完善与尚未研究的部分,包括通过分子动力学模拟计算所得扩散系数与实验值、半经验公式计算值有差异,在复合膜中模拟应用较少等方面。     

饱和液态制冷剂氨的热物理性质的分子动力学模拟

运用分子动力学方法模拟了制冷剂氨的饱和液态热物理性质。采用典型的site-site势能模型模拟了制冷剂氨的饱和液态密度和比焓,将模拟结果与美国国家标准研究所(NIST)数据库的值进行了对比,最大相对偏差分别在1.5%(密度)以内和3.2%(比焓)以内。对比结果表明:采用合理的势能模型和参数,运用该模拟方法预测单一组分工质的热物理性质是可行的。     

A systematic study of DRIE process for high aspect ratio microstructuring

Various MEMS devices like Accelerometers, Resonators, RF- Filters, Micropumps, Microvalves, Microdispensers and Microthrusters are produced by removing the bulk of the substrate materials. Fabrications of such Microsystems requires the ability to engineer precise three-dimensional structures in the silicon substrate. Fabrication of MEMS faces multiple technological challenges before it can become a commercially viable technology. One key fabrication process required is the deep silicon etching for forming high aspect ratio structures. There is an increasing interest in the use of dry plasma etching for this application because of its anisotropic etching behavior, high etch speed, good uniformity and profile control, high aspect ratio capabilities without having any undesired secondary effects i.e. RIE lags, Loading, microloading, loosing of anisotropic nature of etching as aspect ratio increases, micro-grass and even etch stalling. Developing a DRIE micro-machining process requires a thorough understanding of all plasma parameters, which can affect a silicon etching process and their use to suppress the secondary effects. In this paper our intention is to investigate the influence of etching gas flow, etching gas pressure, passivation gas pressure, ICP coil power, Platen power and etch and passivation time sequence on etch rate and side wall profile. Parameter ramping is a powerful technique used to achieve the requirements of high aspect ratio microstructures (HARMS) for MEMS applications by having high etch rate with good profile/CD control. The results presented here can be used to rationally vary processing parameters in order to meet the microstructural requirements for a particular application.     

Fabrication of discrete polystyrene nanoparticle arrays with controllable their structural parameters

We have demonstrated the fabrication of two-dimensionally periodic non-close packed arrays of spherical polystyrene nanoparticles with controllable their structural parameters including diameter and interpartcile distance. The principle of this procedure relies on stepwise integration of spin-coat-assisted colloidal self-assembly of the single layer of close-packed polystyrene nanoparticle on a substrate, and subsequent etching of the particle under atmospheric pressure helium plasma. The plasma process converted the close-packed nanoparticle array into non-close-packed arrangement remaining with unchanged their original spherical shape and periodicity. Owing to the etching process underwent isotropically, the structural parameters could be controlled with nanometric accuracy by the treatment time. The etching rate strongly depended on the working pressure conditions, and the etching rate under 250 Torr was ca. 3 times faster than that of the 760 Torr. The effects of the working pressure indicated the neutral helium radicals and photons diffused from the plasma might be primarily responsible for the etching.     

Anwendungscharakteristika verschiedener Ätzverfahren bei Metallen – Vergleichende Untersuchung metallographischer Ätzverfahren –

Applicability of Different Etching Methods for Metals – Comparing Investigation of Metallographic Etching Procedures The feasibility of different etching techniques in laboratory practice is mainly appointed by the reproducibility of the metallographic micro-structure, which is dependent on the etching method, the etching time and a practical handling of the etching procedure. Comparing investigations concerning the applicability of chemical, electrolytic and ionic etching methods for metals and alloys in electrotechnical industry – with the aim to estimate efficiency and reproducibility of the micro-structure resulting from the different techniques – have been done. Micro-structure estimation will be done by different methods of light-microscopy. In any case physical ion-etching turns out to be the less problematic etching method – in comparison with chemical and electrolytic techniques. Ion etching shows a good reproducibility and allows the simultaneous etching of different materials. The summarizing valuation of the different etching methods includes a list of optimum etching parameters for copper, brass copper-tin and copper-beryllium alloys.     

电化学刻蚀参数对高阻厚壁宏孔硅阵列表面形貌的影响

采用光电化学刻蚀方法,在电阻率为4～5 kΩ·cm的n-型[100]单晶硅片上制备了厚壁有序宏孔硅阵列。通过对比有限元法模拟诱导坑周围的电场分布,研究了刻蚀参数(电解液、光照、电压)对阵列表面形貌的影响。在刻蚀成孔的过程中,诱导坑对孔的限制受电场分布和实验条件的共同影响,出现刻蚀偏离的现象。模拟结果显示,诱导坑上的电场强度沿着单晶硅的[100]和[110]晶向的分布。这种分布的结果是,随着光照强度的提高和刻蚀溶液表面自由能的降低刻蚀由原光刻图形的(110)面向(100)面偏离。提高刻蚀电压可抑制刻蚀偏离,有利于诱导坑快速刻蚀成孔,从而形成规整的厚壁宏孔硅阵列。     

Effect of electroless etching parameters on the growth and reflection properties of silicon nanowires

Vertically aligned silicon nanowire (Si NW) arrays have been fabricated over large areas using an electroless etching (EE) method, which involves etching of silicon wafers in a silver nitrate and hydrofluoric acid based solution. A detailed parametric study determining the relationship between nanowire morphology and time, temperature, solution concentration and starting wafer characteristics (doping type, resistivity, crystallographic orientation) is presented. The as-fabricated Si NW arrays were analyzed by field emission scanning electron microscope (FE-SEM) and a linear dependency of nanowire length to both temperature and time was obtained and the change in the growth rate of Si NWs at increased etching durations was shown. Furthermore, the effects of EE parameters on the optical reflectivity of the Si NWs were investigated in this study. Reflectivity measurements show that the 42.8% reflectivity of the starting silicon wafer drops to 1.3%, recorded for 10 μm long Si NW arrays. The remarkable decrease in optical reflectivity indicates that Si NWs have a great potential to be utilized in radial or coaxial p-n heterojunction solar cells that could provide orthogonal photon absorption and enhanced carrier collection.     

Micro-fabrication techniques applied to aluminosilicate glass surfaces: Micro-indentation and wet etching process

Micro-indentation and HF etching were explored as micro-fabrication techniques applied to glass surfaces. The effects of the aluminosilicate glass composition and of the etching conditions on the etching rate were investigated. It was found that the etching rate increased with increasing the ratio of Al₂O₃ to SiO₂ in the aluminosilicate glass. Etching parameters, such as pH, concentration and temperature of HF acid, had effects on etching rate. However, the effects of these parameters were much smaller at indented area than at non-indented area. The results indicated that the etching rate difference between the two areas, which is one of the key factors in the micro-fabrication technique, could be controlled with these parameters. And the phenomena can be well explained in terms of etching and leaching mechanism of aluminosilicate glass.     

超疏水表面制备方法的比较

超疏水性是一种特殊的润湿性,它是指水滴与表面的静态接触角大于150°或者滑动角小于10°,其最初来源于"荷叶效应".本文对近几年关于超疏水理论和自然界中超疏水现象研究进行介绍,并对超疏水表面的制备方法及其应用进行综述.分别总结了基于模板法、涂覆法、刻蚀法的超疏水表面制备方案的优缺点及其改进措施,重点阐述超疏水表面在金属...     

Simulation of corrosion process for concrete filled steel tubular columns with the cellular automata method

In this paper, from the mesoscopic point of view, under the assumption of metal corrosion damage evolution being a diffusive process, the cellular automata (CA) method was proposed to simulate numerically the uniform corrosion damage evolution of the outer steel tube of concrete filled steel tubular columns subjected to corrosive environment, and the effects of corrosive agent concentration, dissolution probability and elapsed etching time on the corrosion damage evolution were also investigated. It was shown that corrosion damage increases nonlinearly with increasing elapsed etching time, and the longer the etching time, the more serious the corrosion damage; different concentration of corrosive agents had different impacts on the corrosion damage degree of the outer steel tube, but the difference between the impacts was very small; the heavier the concentration, the more serious the influence. The greater the dissolution probability, the more serious the corrosion damage of the outer steel tube, but with the increase of dissolution probability, the difference between its impacts on the corrosion damage became smaller and smaller. To validate the present method, corrosion damage measurements for concrete filled square steel tubular columns (CFSSTCs) sealed at both their ends immersed fully in a simulating acid rain solution were conducted, and Faraday's law was used to predict their theoretical values. Meanwhile, the proposed CA mode was applied for the simulation of corrosion damage evolution of the CFSSTCs. It was shown by the comparisons of results from the three methods aforementioned that they were in good agreement, implying that the proposed method used for the simulation of corrosion damage evolution of concrete filled steel tubular columns is feasible and effective. It will open a new approach to study and evaluate further the corrosion damage, loading capacity and lifetime prediction of concrete filled steel tubular structures.     

Sulphuric acid etching of polyethylene surfaces

The sulphuric acid etching of polyethylene results in the formation of sulphonic groups, varying the surface properties. The study of the groups formed during the etching has been carried out by means of frustrated multiple internal reflection infrared spectroscopy (FMIR). Densities, thermal properties, superficial resistances and resistivities have been correlated with the content of sulphonic groups and treatment time. Moreover, the critical surface tension and platelet adhesion have been examined and related with the change in those properties. Direct sulphonation of polyethylene is a suitable method to change its surface properties, improving the application of this polymer as a biomaterial.     

基于电化学腐蚀法的钨探针制备装置研究

基于电化学腐蚀法制备钨探针的原理,设计了一套钨探针制备装置,并对钨探针制备参数进行了研究。装置的实验部分用于调整探针与电解槽的相对位置和运动参数,控制部分用于监测、控制并记录电化学反应的状态。与传统腐蚀探针相比,该装置通过控制电路控制探针腐蚀过程中运动参数,获得了形状可控的大长径比探针;同时通过精确控制腐蚀反应时间,可制备针尖曲率半径范围为5~20 nm的探针。