高压下制备的累托石/酚醛树脂复合材料微结构和热性能研究

 采用物理方法在高压下制备了酚醛树脂（PF）/累托石（REC）纳米复合材料,用X射线衍射（XRD）、透射电子显微镜（TEM）及热分析（DSC/TGA）等方法,研究了复合材料的物相、显微结构以及热学性能。结果表明,不通过层间高分子聚合反应,不预先对累托石进行有机化处理,在高压下,由聚合物分子插入粘土层间,可以形成剥离型树脂/粘土纳米复合材料,并且其热学性能发生了较大的改变。     

纳米粘土增强环氧树脂复合材料抗原子氧性能的研究

本文采用激光爆破法高能原子氧束源研究了纳米粘土增强环氧树脂复合材料的抗原子氧性能. 研究了四种样品：纯环氧树脂,纳米粘土含量为1 wt%,2 wt%和4 wt%的纳米粘土增强环氧树脂复合材料,结果表明腐蚀深度随着纳米粘土含量的增加而降低,当掺杂纳米粘土含量为4 wt%时,腐蚀深度为纯环氧树脂腐蚀深度的28%∽37%;X射线光电子能谱(XPS)分析表明原子氧轰击后,材料表面C-C/C-H键比例减少,C-O键、酮类比例增加,表面氧化程度增加,掺杂纳米粘土的材料表面生成了新的碳酸盐,掺杂4 wt%纳米粘土的复合材料表面氧化程度增加最小;扫描电子显微镜(SEM)结果显示含有纳米粘土的复合材料表面被原子氧轰击后在纳米粘土团簇处形成了“块状”物质,掺杂4 wt%纳米粘土的复合材料,“块状”物质尺寸和分布密度最大;综合腐蚀深度,XPS,以及SEM结果表明,虽然所有表面都一定程度地被原子氧腐蚀和氧化,但掺杂纳米粘土的复合材料表面由于生成了“块状”物质,阻挡了原子氧进一步腐蚀其下的材料,提高了抗原子氧性能.     

纳米粘土增强环氧树脂复合材料抗原子氧性能的研究（英文）

本文采用激光爆破法高能原于氧束源研究了纳米粘土增强坏氧树脂复合材料的抗原子氧性能.研究了四种样品:纯环氧树脂,纳米粘土含量为1 wt%,2 wt%和4 wt%的纳米粘土增强环氧树脂复合材料,结果表明腐蚀深度随着纳米粘土含量的增加而降低,当掺杂纳米粘土含量为4 wt%时,腐蚀深度为纯环氧树脂腐蚀深度的28%～37%;X射线光电子能谱(XPS)分析表明原子氧轰击后,材料表面C-C/C-H键比例减少,C-O键、酮类比例增加,表面氧化程度增加,掺杂纳米粘土的材料表面生成了新的碳酸盐,掺杂4 wt%纳米粘土的复合材料表面氧化程度增加最小;扫描电子显微镜(SEM)结果显示含有纳米粘土的复合材料表面被原子氧轰击后在纳米粘土团簇处形成了"块状"物质,掺杂4 wt%纳米粘土的复合材料,"块状"物质尺寸和分布密度最大;综合腐蚀深度,XPS,以及SEM结果表明,虽然所有表面都一定程度地被原子氧腐蚀和氧化,但掺杂纳米粘土的复合材料表面由于生成了"块状"物质,阻挡了原子氧进一步腐蚀其下的材料,提高了抗原子氧性能.     

固体NMR 研究PMMA 纳米复合材料结构与受限链运动

聚合物/无机纳米复合材料的微观结构和动力学决定了其宏观性能,阐明无机纳米材料对复合材料结构和动力学的影响,对认识材料结构-性能关系及设计新材料都具有重要意义．该文通过乳液聚合方法合成了聚甲基丙烯酸甲酯/锂藻土(PMMA/Laponite)纳米复合材料,采用1H MAS 和¹³C CPMAS、弛豫时间及¹³C 化学位移各向异性谱(SUPER)等多种固体NMR 技术,详细研究了无机纳米材料的界面改性及其对纳米复合材料的微观结构和动力学的影响．¹H MAS 和¹³C CPMAS 实验表明,有机改性剂与锂藻土形成强的有机-无机界面相互作用,¹³C 纵向弛豫时间实验表明,PMMA 及其锂藻土纳米复合物均含有刚性和柔性两个组分,而纳米复合物中的聚合物链运动相对较低,特别是其中PMMA 的酯基分子运动明显受限．进一步的¹³C SUPER 实验表明,PMMA 酯基的化学位移各向异性在加入锂藻土后发生变化,预示酯基与锂藻土表面的羟基可能存在氢键作用而导致聚合物的链段运动进一步受限,上述纳米尺度受限效应提高了复合材料的玻璃化转变温度．     

聚合物电导率对0-3型压电复合材料极化性能的影响

建立了0-3型压电复合材料的等效电学模型.分析了聚合物电导率对复合材料极化性能的影响，研究了聚苯胺改性0-3型锆钛酸铅/聚偏氟乙烯复合材料极化性能与聚合物电导率之间的关系.理论分析和实验结果均表明，提高聚合物电导率可以提高复合材料的极化性能. 关键词： 压电复合材料 电导率 极化 聚偏氟乙烯     

导电复合材料的研制

为了适应Z-pinch物理实验对新材料的要求，2003年来对导电复合材料进行了初步研制。由于导电聚合物结构的特殊性，导致了导电聚合物机械加工性能很差，聚吡咯是一种具有较好的热、化学氧化和光照稳定性导电聚合物，因此利用有机材料作为基体，吸附吡咯同时进行氧化聚合，可得到性能较好导电复合材料。在导电聚合物的研制过程中，主要涉及基体材料的选择、氧化剂的选择以及反应时间对复合材料的表面电阻的影响。     

导电聚合物微米/纳米结构的制备和性质

文章综述了导电聚合物微米／纳米结构(微米管、纳米管、纳米线和微米球等)近几年来所取得的研究进展．重点介绍了三种制备方法(模板合成、无模板法、电纺丝技术)和导电聚合物微米／纳米管的电学、力学、热学、磁学等性能．     

一种表面具有纳米孔穴的聚合物绝缘子

绝缘体表面结构和微观形貌对提高器件真空闪络特性有重要影响。首次提出了表面具有均匀分布纳米级空穴聚合物绝缘子的化学制备方法。通过本体聚合制备纳米级二氧化硅颗粒均匀分布的交联聚苯乙烯复合材料,机械加工成聚合物绝缘子后,采用氢氟酸化学腐蚀的方法将绝缘子表面氧化物颗粒去除。采用透射电子显微镜、表面电阻率和短脉冲高压测试平台分别对处理前后绝缘子的表面形貌和绝缘等性能进行了表征,结果表明:处理后的交联聚苯乙烯复合材料绝缘子的表面形成了20~50 nm直径的空穴,空穴的大小和数量分布分别由二氧化硅颗粒的粒径和加入量控制。这种具有特殊表面结构的新型绝缘子的沿面闪络电压较纯交联聚苯乙烯绝缘子提高了15%~20%,并保持了较好的力学及加工性能。研究方法和实验结果对聚合物绝缘子的表面结构设计及高性能绝缘子的研制提供了一种新的途径。     

导电PI/纳米炭黑复合材料的制备和测试

以均苯四甲酸二酐、4,4'-二氨基二苯醚、炭黑为主要原材料制成填充型导电PI/纳米炭黑复合材料.经电子显微镜及伏安法等对其性能进行表征,结果发现:掺入纳米炭黑能使PI的导电能力增强,且这种能力随炭黑掺入量增加而提高,但是炭黑含量继续增加却会引起聚合物体系中团聚现象的加剧,导致导电能力下降,当掺入量为6%时复合材料导电性能达最好,电阻为4.02×106 Ω.     

导电聚合物自组装纳米器件

导电聚合物自20世纪70年代以来得到了广泛的研究．然而，关于聚合物纳米器件的研究则鲜有报导．从纳米尺度上研究导电聚合物，不仅有利于从更小的尺度上解析聚合物的光电性能、电荷传输机理，也可以将导电聚合物和纳米电子学有机地结合起来，发展聚合物纳米电子学的研究．文章介绍了最近由胡文平等采用自组装的方法构筑的聚合物纳米器件和在纳米器件中观察到的一些有趣的现象．     

Influence of aspect ratio on barrier properties of polymer-clay nanocomposites

The barrier properties of polymer-clay nanocomposites, with far less inorganic contents of layered-silicate fillers, are remarkably superior to those of neat polymers or their conventional counterparts. A simple renormalization group model is proposed to assess the influence of geometric factors (such as aspect ratio, orientation, and extent of exfoliation) of layered-silicate fillers on the barrier properties of polymer-clay nanocomposites. The results show that the aspect ratio of exfoliated silicate platelets has a critical role in controlling the microstructure of polymer-clay nanocomposites and their barrier properties. The estimated percolation thresholds of clay content for minimum permeability are in good agreement with experimental data.     

Prediction of complex dielectric constants of polymer-clay nanocomposites

In this Letter, simple theoretical models are presented to predict the influence of aspect ratio, orientation, distribution, and interphase of layered silicates on the dielectric properties of polymer-clay nanocomposites. The predictions are in good agreement with experimental data. The results show that the morphology of the clay fillers and the thickness and dielectric properties of the interphases play an important role in determining the dielectric properties of polymer-clay nanocomposites.     

Preparation and Mechanical and Tribological Properties of High-Density Polyethylene/Hydroxyapatite Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with hydroxyapatite nanorods (nHA) were fabricated by means of extrusion and injection molding. The thermal, mechanical, and dry sliding wear properties of HDPE-based nanocomposites filled with nHA loadings up to 20 wt% were investigated. The results of mechanical property characterization showed that nHA additions improved the hardness, elastic modulus, and yield strength of HDPE at the expense of its tensile ductility and impact strength. Thermogravimetric analysis and heat deflection temperature measurements revealed that nHA fillers are very effective to enhance the thermal stability of HDPE. The wear behavior of HDPE/nHA nanocomposites was studied using a pin-on-disk tribometer. nHA fillers of a large aspect ratio improved the wear resistance of HDPE substantially because of their load-bearing effect and the formation of a continuous transfer film on the steel counterface.     

The effects of ultrasound on organoclay dispersion in the PP matrix

PP/MMT nanocomposites were prepared by solution intercalation using sonication and quiescent conditions, and the effects on the morphological, thermal and mechanical properties were evaluated by WAXD, TEM, DMA, TGA and DSC analyses. The present study aims to clarify the effects of ultrasound use on the organoclay surface with different amounts of organic modifiers and on the exfoliation processes. The sonication process decreased around of 200 nm the aspect ratio of C15A organoclay. Besides, the effectiveness of the ultrasound process was only achieved with the C15A system because there is a small energetic barrier between their layers (clay with larger d 001). The sonication process increased the exfoliation and distribution of the C15A platelets in the PP matrix, increasing by 5% its reinforcement capacity. However, for I44P system, the use of ultrasound did not show any significant effect on the morphology and consequently on the final properties of the PP matrix. The T(c) temperature and the thermal stability of the PP nanocomposites were increased, independent of the clay type or of the ultrasound use.     

High-Performance Poly(vinyl alcohol) Nanocomposites Filled with Individual Montmorillonite Nanolayers

Filling poly(vinyl alcohol) (PVA) with clay, typically montmorillonite (MMT), has been proven to be an attractive option to meet the high-performance requirements of PVA-based materials. In previous reports MMT or organophilic MMT (OMMT) were directly used as fillers. As a result, both exfoliated and intercalated MMT structures coexisted in the resultant nanocomposites. However, there is still a large gap between these nanocomposites and ideally designed ones where individual clay nanolayers (CNLs) are expected to be uniformly dispersed in the PVA. With this in mind, an ameliorative solution casting process is proposed here to prepare PVA nanocomposites. For this purpose the CNLs were prepared ahead of time by exfoliation of MMT in water and then used as fillers. Assessment of the dispersion state of the CNLs in PVA revealed that they (≤5.0 wt%) were randomly and uniformly dispersed (down to the level of individual silicate layers) in and formed strong interfacial interactions with the PVA. This resulted in significantly enhanced physical properties of the resultant nanocomposites relative to neat PVA. In particular, a 104.7% increment in the yield stress was achieved with 5.0 wt% CNLs, much larger than the 15–70% increments of previous PVA nanocomposites using MMT or OMMT as fillers. Additionally, excellent optical clarity of the PVA was obtained for the nanocomposites.     

Application of Nanoparticles in Polymers for Electronics and Electrical Engineering

Different organophilic layered silicates and a modified hydrotalcite were used as functional nanofillers for thermoplastic and thermosetting polymers. Polyamide 6 (PA6) and poly(butylene terephthalate) silicate nanocomposites were prepared by melt compounding using a twin‐screw extruder. The morphology of the materials was investigated by transmission electron microscopy and small‐angle X‐ray scattering, and was found to be characterized by homogeneous dispersion of high aspect ratio silicate layers in the polymer matrix. The PA6 nanocomposite displayed excellent thermo‐mechanical properties at low filler loadings and improved barrier properties. Epoxy nanocomposites have also been prepared and characterized with regard to their morphology and their water vapor permeability.     

Elastic interactions and stability of clay-filled lamellar phases

High aspect ratio clay particles dispersed in a lamellar matrix composed of a block copolymer or a lyotropic smectic are expected to orient with the lamellae. Under such conditions, the smectic medium transmits elastic forces among particles in addition to the usual forces produced by dispersion and electrostatic interactions. We compute these elastic forces and explore their influence on the thermodynamics of lamellar-clay dispersions. It turns out that the large aspect ratio of the clay implies a long range of interaction at the two particle level. Consequently, virial expansions break down at very low loadings of particles. We examine the thermodynamic behavior of assemblies of flexible and rigid clay plates in both dilute and semidilute concentration regimes. Our results should have implications for the design of nanocomposites formulated with block copolymers and lyotropic liquid crystals. Received 11 August 2000     

Simple "kink" model of melt intercalation in polymer-clay nanocomposites

We propose a simple semiphenomenological model to describe the dynamics of polymer melt intercalation in the gallery between the adjacent clay sheets in polymer-clay nanocomposites. Within this model, the intercalation process is driven by the motion of localized excitations ("kinks") which open up the tip between the clay sheets. These kinks belong to a novel type of solitonlike excitations that appear due to the interplay between the double-well potential of the clay-clay long-range interaction, bending elasticity of the sheets, and external shear force. We find that the kink solutions can exist only if applied shear is sufficiently strong, in a qualitative agreement with experimental data.     

Effect of Rubber Content of ABS on the Mechanical Properties of ABS/Clay Nanocomposites

One approach to improve the impact strength of acrylonitrile–butadiene–styrene (ABS)/clay nanocomposites is to increase rubber content. To investigate the effect of the rubber content of ABS on the mechanical properties of the ABS/clay nanocomposites, other parameters were fixed and ABS/clay nanocomposites containing various rubber contents were prepared in this study. Also the effect of the UV stabilizer on the mechanical properties of ABS/clay nanocomposite was studied. For addition of 3 wt% clay, ABS nanocomposite with 35 wt% content of rubber displayed the highest reinforcement ratio for tensile properties and impact strength.     

Effect of High Aspect Ratio Fillers on the Performance of Styrene-Butadiene Rubber

Among the many material performance properties of vulcanized elastomers for tire tread application, rolling resistance and wet traction are particularly important since both greatly impact fuel efficiency and traction of a vehicle. Rolling resistance and wet traction are generally negatively correlated, i.e., with the increase in rolling resistance of a tire, its wet traction decreases. Silica nanofillers are often used for achieving the desired balance of wet traction and rolling resistance. However, the high cost of silica limits its wide spread application. In this research we studied the effects of using fillers with different aspect ratios (calculated by dividing the long dimension of a filler by its short dimension) on the performance of vulcanized styrene butadiene rubber (SBR), a common rubber for tire tread application. Three high aspect ratio fillers were used: aragonite calcium carbonate, wollastonite and carbon nanofiber. For comparison purpose, spherical silica filler was also included. We found that the high aspect ratio fillers were efficient in improving the wet traction and rolling resistance as well as enhancing the mechanical energy dissipation of SBR. Among the three high aspect ratio fillers studied, wollastonite provided the best wet traction and rolling resistance balance due to its high aspect ratio and compatibility with the base rubber. The effects of fillers induced crosslinking on the dynamic performance were also discussed.