耗散粒子动力学模拟Nafion膜和PVA/Nafion共混膜的介观结构

采用耗散粒子动力学模拟方法研究了水化Nafion膜和水化聚乙烯醇(PVA)/Nafion共混膜的微结构.模拟结果表明水化Nafion膜和水化PVA/Nafion共混膜均能形成相分离的微结构.在水化Nafion膜中,水与磺酸根混合形成管状的水团簇.随着膜内水含量增多,管状水团簇的尺寸逐渐变大并在膜内形成连续的水通道.在水化PVA/Nafion共混膜中,PVA、水、磺酸根混合形成亲水性区域.共混膜中PVA的质量分数和水含量共同影响膜的微结构.当膜中PVA质量分数较低时,PVA主要分布在Nafion的磺酸根基团周围;PVA质量分数升高后,PVA会在膜内单独成一相.当膜中的水含量相对较低时,水分子会溶解于PVA中,此时膜内不存在单独的水团簇;膜中的水含量增多后,膜内会形成接近于球形的水团簇.本文工作可为直接甲醇燃料电池用的PVA改性Nafion膜的开发提供参考.     

PP-g-(GMA-co-St)对PA6/PC共混物的反应增容作用

用红外、扫描电镜、熔体流动速率和力学性能等测试方法,研究了甲基丙烯酸缩水甘油酯(GMA)和苯乙烯(St)多单体熔融接枝聚丙烯[PP-g-(GMA-co-St)]对PA6/PC共混物的反应增容作用.研究结果表明,在熔融共混过程中,PP-g-(GMA-co-St)中的环氧基与PA6的端氨基及PC的端羟基原位生成的接枝共聚物有效地降低了共混物相间的界面张力,明显提高了共混物相界面的粘着力.少量的PP-g-(GMA-co-St)就能使PA6和PC的相容性得到显著改善.当PP-g-(GMA-co-St)的质量分数为10%时,共混物分散相的相区尺寸细化到0.2μm,其力学性能也有较大提高.PA6/PC/PP-g-(GMA-co-St)共混物的力学性能均衡,达到了弹性体增韧体系难以达到的效果.即使PP-g-(GMA-co-St)组分含量为20%时,共混物仍能保持较好的力学性能,特别是在共混物的韧性得以提高的同时,其强度和伸长率也提高.     

磨盘碾磨制备PA6/PP/SBS共混物的结构与性能

采用磨盘形力化学反应器,在室温下制备了PA6/PP超细混合粉体,与SBS共混制得PA6/PP/SBS共混物,测定了材料的力学性能并用TEM研究了材料在不同加工温度下相结构的变化.结果表明,通过固相力化学粉碎制备的PA6/PP混合微粉,改善了PA6与PP和SBS的相容性,促进了PA6及PP的分散和与SBS的相界面结合.在微粉填充量为4%～8%(质量分数)时,材料的拉伸强度大幅度提高,扯断伸长率保持不变.加工温度变化引起材料相结构的变化对材料性能产生显著影响.在PP熔融温度下加工,PP粒子产生粘连形成链状结构,可提高材料的力学性能.     

材料研究中的介观模拟方法

介绍了材料研究中的蒙特卡罗、元胞自动机和耗散粒子动力学三种介观模拟方法的原理和应用。重点阐述了耗散粒子动力学方法在材料研究领域中的应用,包括嵌段共聚物在水溶液中的聚集行为、聚合物和表面活性剂的相互作用、复杂流体流动的耗散粒子动力学研究、嵌段共聚物的微相分离等,除此之外,笔者还初步探索了耗散粒子动力学在熔体静电纺丝领域的...     

丁二酰亚胺类分散剂体系的介观模拟研究

以润滑油添加剂丁二酰亚胺类分散剂的分散性能为研究目标，运用耗散粒子动力学介观模拟方法考察了分散剂结构、用量、与润滑油的相互作用等因素对分散性能的影响，并用分子模拟方法估算了模拟需要的介观参数.通过恰当地定义分散性能，选择合适的模型化合物，得到了与实验研究定性一致的模拟结果.为润滑油分散剂的分子设计提供有益的理论指导.     

PA6/HIPS/PP-g-(GMA-co-St)反应共混体系的研究

通过扫描电镜、热分析、熔体流动速率、熔融扭矩和力学性能等测试方法研究了甲基丙烯酸缩水甘油酯(GMA)和苯乙烯(St)多单体熔融接枝聚丙烯[PP-g-(GMA-co-St)]对PA6/HIPS共混物的熔融流变性能、结晶行为、相形态和力学性能的影响.结果表明,在熔融共混过程中,PP-g-(GMA-co-St)中的环氧基与PA6的端氨基原位生成的接枝共聚物有效地降低了共混物的界面张力,提高了共混物的界面粘着力,使共聚物的流动速率降低,熔融扭矩提高;PA6分子链的规整性降低,结晶完善性变差.在PP-g-(GMA-co-St)的质量分数为10%时,共混物分散相的尺寸明显减少,力学性能得到较大提高;其中冲击强度超过纯PA6,达到HIPS水平.通过反应共混,制备了力学性能均衡的PA6/HIPS/PP-g-(GMA-co-St)共混物合金.     

端羟基聚丁二烯/增塑剂共混物相容性的分子动力学模拟和介观模拟

应用分子动力学(MD)和介观动力学(MesoDyn)模拟方法对固体推进剂中端羟基聚丁二烯(HTPB)与增塑剂癸二酸二辛酯(DOS)、硝化甘油(NG)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、HTPB/增塑剂共混物的密度、内聚能密度、溶度参数和共混物分子间的Flory-Huggins作用参数及结合能等进行了模拟计算, 通过比较溶度参数差值(Δδ)的大小、模拟前后体系密度变化情况均可以预测HTPB与增塑剂的相容性, 结合能的分析揭示了HTPB/增塑剂共混物组分间的相互作用及本质. 将Flory-Huggins作用参数转化为MesoDyn模拟的输入参数, 采用MesoDyn模拟方法对HTPB/增塑剂共混体系的介观形貌与动力学演变过程进行了研究, 通过模拟得到的等密度图、自由能密度和有序度参数等可以判断共混体系的相容性. MD和MesoDyn模拟结果均表明: HTPB/DOS属于相容体系, 而HTPB/NG属于不相容体系, 其结论与实验结果一致.     

淀粉微球形成过程的介观模拟及实验

以环己烷为油相、淀粉乳液为水相、Span60和Tween60为乳化剂,对淀粉微球的形成过程进行了耗散粒子动力学(DPD)模拟及实验研究.模拟结果表明,淀粉微球的形成过程存在四个阶段,即淀粉与乳化剂分子无规则分散阶段、小聚集体形成阶段、球状聚集体形成阶段和稳定平衡阶段,并且发现油水比是影响聚集体是否能形成球状的关键因素.油水比小于7的条件下,油水两相分离较难,水相呈现片状、十字型状、柱状及椭球状等形状;当油水比增加到8,水相能形成微球且微球粒径随油水比增加而减小.同时实验结果表明,油水比为8时,微球粘连,几乎看不清球状形貌,油水比为10～20时,微球的粒径随油水比的增大而减小.实验结果很好地吻合了模拟结果.     

周期性变电场下熔体静电纺丝射流的介观模拟

利用介观模拟的耗散粒子动力学法, 对纺丝射流稳定直线段区域进行变电场模拟, 并以三维的射流路径呈现出来. 研究了不同控制频率下的变电场对聚合物分子链的运动情况、 射流直径及下落行为的影响. 结果表明, 与稳定电场相比, 周期性改变电场能够有效提高分子链的拉伸, 使射流直径减小, 较低的控制频率能够加速射流的下落, 从而获得较细的纤维.     

PA6／PET共混体系的X射线衍射分析

用宽角Ｘ射线衍射分析,考察尼龙６／ＰＥＴ共混体系的结晶态,表明在共混物中尼龙６和ＰＥＴ是各自结晶的,即晶相分离的。研究了结晶条件,组份比等对晶态结构的影响,发现共混体系相对结晶度低于纯组份的算术加和,说明共混体系的结晶相分离过程中,由于存在相互作用导致的干扰,使结晶度下降。     

聚苯硫醚合成宏观动力学探讨

聚苯硫醚(PPS)的合成是特殊的缩聚反应[1],在合成过程中存在快慢不同的两个反应,快反应是低分子缩合,慢反应是AB型自缩聚,因此可称为(A2B2)→AB型缩聚反应。本文探讨生产聚苯硫醚时温度等反应条件对反应程度和产物熔点的影响。1　实验合成实验的装置和产品的分析测试同前文[1]。所使用的两种溶剂(六甲基磷酰三胺和N 甲基吡咯烷酮)只能使阳离子溶剂化:Na2S+2xNMP2Na(NMP)+x+S2-(1)这一溶剂化作用的稳定常数较大,溶剂将钠离子包围起来,使硫离子充分裸露,具有更高的亲核性[2],这种高活性,促使它首先与对二氯苯进行反应,生成对氯硫…     

Polymer blends of polyamide-6 (PA6) and poly(phenylene ether) (PPE) compatibilized by a multifunctional epoxy coupler

A tetrafunctional epoxy monomer, N,N,N′-N′-tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM), has demonstrated to be a highly efficient reactive compatibilizer in compatibilizing the immiscible and incompatible polymer blends of polyamide-6 (PA6) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE). This epoxy coupler can react with both PA6 and PPE to form various PA6-co-TGDDM-co-PPE mixed copolymers. These interfacially formed PA6-co-TGDDM-co-PPE copolymers tend to anchor along the interface to reduce the interfacial tension and result in finer phase domains and enhanced interfacial adhesion. A simple one-step melt blending has demonstrated to be more efficient in producing a better compatibilized PA6/PPE blend than a two-step sequential blending. The mechanical property improvement of the compatibilized blend over the uncompatibilized counterpart is very drastic, by considering the addition of a very small amount, a few fractions of 1%, of this epoxy coupling agent. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1805–1819, 1998     

Electrical properties of ion-implanted poly(p-phenylene sulfide)

Ion implantation of impurities into thin films of poly(p-phenylene sulfide) (PPS) is found to increase the conductivity of the material by up to 12 orders of magnitude. The increase is stable under exposure to ambient conditions, in contrast to the instability of the conductivity increases in PPS produced by chemical doping with AsF₅. PPS films 0.1–0.2 μm thick are spin cast from solution onto interdigitated electrodes patterned on an oxidized silicon substrate. The room-temperature interelectrode resistance is measured as a function of implantation fluence. An estimate of film conductivity is obtained from this resistance with a simple model for the electrode and film geometry. A first experiment yielded similar conductivity increases for implantation of either arsenic or krypton. At a fluence of 1 × 10¹⁶cm^?;2, which corresponds to an average impurity concentration of 2.5 × 10²¹cm^?3, the conductivity reaches an apparently saturated value of 1.5 × 10^?5 (Ω cm)^?1. Infrared spectra of the films before and after implantation suggest that crosslinking may be present in the implanted films, and Auger studies show stoichiometric changes throughout the implanted layer. These results suggest that the observed conductivity changes are the result of molecular rearrangements produced by the implantation rather than the result of specific chemical doping. Specific chemical doping may, however, explain the results of a second experiment in which implantation of bromine resulted in substantially larger conductivities found to increase at an approximate linear rate from a value of 1.0 × 10^?4 (Ω cm)^?1 at a fluence of 1 × 10¹⁶ cm^?2 to a value of 4.0 × 10^?4 (Ω cm)^?1 at a fluence of 3.16 × 10¹⁶ cm^?2.     

Influence of microstructure and deformation behavior on toughening of reactively compatibilized polyamide 6 and poly(ethylene-co-butyl acrylate) blends

Influence of microstructure on impact toughness and fracture behavior of PA6 and EBA blends reactively compatibilized by EBA-g-MAH was quantitatively studied. The reactively compatibilized blends showed better distribution of elastomeric EBA particles in the PA6 matrix and the presence of EBA-g-MAH resulted in considerable reduction of interfacial tension between the component polymers. The interfacial adhesion between the PA6 and EBA phase in the compatibilized blends was enhanced by the interfacial reaction between the amide end-groups of PA6 and maleic anhydride group of EBA-g-MAH compared to uncompatibilized blends. The matrix ligament thickness and particle diameter values were lower than the predicted critical values and were responsible for the ductile behavior of the compatibilized blends. Stress whitening around the notch occurred in all the compatibilized blends which was the major energy dissipation zone in the blends. Matrix shear yielding or plastic flow without crazing was the dominant deformation mechanism in the tough compatibilized blends. There was no sign of shear yielding during impact fracture of the uncompatibilized blends where the elastomeric particles were completely dislodged from the matrix.     

Drawing of poly(p-phenylene sulfide) by solid-state coextrusion

The effects of drawing temperature on the physical and mechanical properties of poly(p-phenylene sulfide) have been studied. A melt-quenched film was drawn by solid-state coextrusion both below (75°C) and above (95 and 110°C) the glass transition temperature T_g (85°C) of PPS. The maximum extrusion draw ratio (EDR_max) increased from 3.4 to 5.6 with increasing extrusion temperature T_e from 75 to 110°C. It was found that extrusion drawing just above the T_g of PPS (95°C) produced more stress-induced crystals. A high efficiency of draw in the amorphous region was achieved by extrusion at T_e-75°C. The tensile modulus at EDR_max decreased from 5.1 to 3.5 GPa with increasing T_e from 75 to 110°C. The low efficiency of draw for the samples extruded at 110°C is explained in terms of disentanglement and chain slippage during drawing due to a less effective network.     

Ultraviolet photoelectron spectroscopy of poly(p-phenylene sulfide) (PPS)

Ultraviolet photoelectron spectra were measured for films of poly(p-phenylene sulfide) (PPS) prepared by vacuum evaporation. The threshold ionization potential was determined to be 6.0 ± 0.1 eV. The peaks in the photoelectron spectra are assigned by comparison with theoretical calculations, and the π bandwidths of PPS and related compounds are discussed.     

Effect of POSS on morphology and properties of poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 blends

Poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 (PPO/PA6) (50/50 w) blends filled with epoxycyclohexyl polyhedral oligomeric silsesquioxane (POSS) were prepared via melt-mixing. The reactions between POSS and PPO/PA6 blends were studied by Fourier transform infrared spectroscopy, end group and gel content tests. The morphology of PPO/PA6/POSS composites was observed by field emission scanning electron microscope and transmission electron microscope. As a chain extender and a crosslinking agent for PA6, POSS largely affected the morphology of the composites, which was mainly dependent on the melt-viscosity ratio and interfacial tension between the components. With increasing POSS content from 2 to 4 phr, the morphology of the composites transformed from droplet/matrix to co-continuous morphology. The PPO/PA6/POSS composites with co-continuous morphology had the better mechanical properties than those with droplet/matrix morphology. Dynamic mechanical thermal analysis showed that the addition of POSS increased the T_g of PA6.     

Effects of solvent treatment on crystallization kinetics of poly(p-phenylene sulfide)

Isothermal melt crystallization kinetics were investigated by differential scanning calorimetry (DSC) for virgin and α-chloronaphthalene solvent-treated poly(phenylene sulfide) (PPS) systems. The overall crystallization rates were found to be much faster for the solvent-treated PPS than for the virgin neat PPS. Additionally, the Avrami crystallization plot for the solvent-treated PPS samples appeared as two straight portions with an apparent discontinuity, but as a continuous straight line for the virgin PPS system. After the treatment of solvent dissolution and subsequent drying, the residual trace α-chloronaphthalene, upon being quenched to the crystallization temperatures, initiated some localized solvent-induced nuclei-like crystals in PPS. It was the nuclei that enhanced secondary crystallization in treated PPS during the second stage, and the higher extents of secondary crystallization in the solvent-treated PPS caused the apparent discontinuous break in the Avrami plots. The causes for the difference were explained and the mechanism of the sequential primary/secondary crystallization kinetics for the solvent-treated PPS was satisfactorily described with a proposed series-parallel crystallization model. ©1995 John Wiley & Sons, Inc.     

Dissipative particle dynamics study on the interfaces in incompatible A/B homopolymer blends and with their block copolymers

Dissipative particle dynamics, a simulation technique appropriate at mesoscopic scales, has been applied to investigate the interfaces in immiscible binary A/B homopolymer blends and in the ternary systems with their block copolymers. For the binary blends, the interfacial tension increases and the interface thickness decreases with increasing Flory-Huggins interaction parameter chi while the homopolymer chain length is fixed. However, when the chi parameter and one of the homopolymer chain length is fixed, increasing another homopolymer chain length will induce only a small increase on interfacial tension and slight decrease on interface thickness. For the ternary blends, adding the A-b-B block copolymer will reduce the interfacial tension. When the mole number of the block copolymer is fixed, longer block chains have higher efficiency on reducing the interfacial tension than the shorter ones. But for the block copolymers with fixed volume fraction, shorter chains will be more efficient than the longer ones on reducing the interfacial tension. Increasing the block copolymer concentration reduces interfacial tension. This effect is more prominent for shorter block copolymer chains.