PP/POE共混物的热行为与晶态结构

采用双螺杆挤出机熔融共混制备了不同组成的聚丙烯(PP)/乙烯-辛烯弹性体(POE)共混物,利用差示扫描量热仪、偏光显微镜和广角X射线衍射系统研究了共混物的热行为与晶态结构。结果表明PP与POE之间具有一定的相容性,POE的异相成核作用提高了共混物中PP的结晶温度和结晶速率,有效地诱导β晶型PP的形成,增大了共混物中α晶型和β晶型PP的晶面表观厚度。另一方面,由于POE与PP之间存在较强的相互作用,POE大分子链使PP分子链的扩散和堆积受阻,从而导致PP/POE共混物总结晶度的降低。     

液晶聚合物β成核剂/等规聚丙烯的等温结晶动力学和熔融行为

将主链型液晶聚酯(PBDPS)大分子β成核剂与等规聚丙烯(i PP)熔融共混,得到不同添加量的i PP/PBDPS样品。利用差示扫描量热分析、X射线衍射、偏光显微镜等研究了i PP和PBDPS共混物的等温结晶动力学、结晶熔融行为、晶型结构和结晶形态。结果表明,i PP和i PP/PBDPS共混物的等温结晶动力学适用于Avrami方程,Avrami指数(n)从2. 62～2. 81变为2. 60～3. 25,晶体的生长方式为二维生长与三维生长并存。PBDPS起到异相成核作用,i PP结晶速率常数(K)随着PBDPS的添加而增大,半结晶时间(t1/2)随之缩短。使用Arrhenius方程计算了等温结晶活化能,并通过HoffmanWeeks外推法得到了i PP/PBDPS中α、β晶的平衡熔点。液晶高分子PBDPS能有效诱导i PP形成β晶型,β晶含量随着PBDPS添加量与结晶温度的提升而增大,当PBDPS质量分数为4%,结晶温度为130℃时,β晶含量高达92. 5%。     

从β-聚丙烯到β-聚丙烯共混物

相对于聚丙烯(PP)共混物,β-PP共混物研究很少。文中对本实验室近几年开展的β-成核PP与聚苯乙烯(PS)、丙烯腈-苯乙烯共聚物(AS)、丙烯腈-丁二烯-苯乙烯共聚物(ABS)、尼龙(PA)、对苯二甲酸乙二醇酯(PET)共混物的制备、结构与性能进行了总结。重点讨论了不同第二组分及其用量、结晶度与极性,增容和制备方法等对PP共混物的β-成核作用的影响。观察到PS、AS和ABS对β-成核作用影响很小,可获得高β-晶含量的PP共混物。β-成核PP与PA、PET共混物的β-成核作用取决于制备方法,降低PET结晶度的方法和加入相容剂有利于共混物β-晶的形成。第二组分极性并不是影响共混物β-成核作用的主要因素。     

二核铝酸酯对碳酸钙的改性作用及应用研究

用经二核铝酸酯处理过的L-CaCO_2与聚丙烯(PP)共混,共混物的力学性能和扫描电镜观察均说明这些铝酸酯有显著的隅联作用。以2DH-306作偶联剂,当共混物的L-CaCO_2/PP<25/75时,共混物的冲击强度比PP平均高出10kJ/m~2,比未改性的L-CaCO_2的共混物高出近30kJ/m~2。所用的L-CaCO_3对PP的β-晶有成核作用,二核铝酸酯对此作用有增强的协同效应。共混物PP结晶中的β-晶含量对共混物的断裂伸长率有重大影响。     

DCP用量对PP／EPDM共混物性能和形态的影响

用动态硫化法制备的PP／EPDM共混型热塑性弹性体的性能明显优于直接共混型PP／EPDM热塑性弹性体,这是由于模量低的EPDM柔性长链经化学交联后,强化对PP的增韧效果,而交联后又被扯断细化的EPDM的颗粒,改变了因EPDM相互缠结所导致的熔融粘度大,加工性能差的缺陷。制备PP／EPDM热塑性弹性体的关键是动态硫化,由于PP／EPDM共混物的动态硫化是一个融物理共混、化学引发交联和剪切细化分散为一体的复杂过程,材料的性能除决定于组成、组分性能和化学交联体系外,还强烈依赖于所采用的共混工艺方式及其条件。本章采用过氧化二异丙苯（DCP）作为硫化剂,研究了过氧化物用量对动态硫化PP（K8303）／EPDM共混物性能和形态的影响。     

利用超临界CO2调控聚合物二元共混物的相形貌及力学性能

共混物的相态结构在很大程度上决定了共混物的物理性质。本工作以超临界CO_2为溶剂,通过改变工艺来调控聚丙烯(PP)/三元乙丙橡胶(EPDM)共混物的相形貌,进而利用动态力学分析(DMA)仪研究其力学行为。结果表明,利用CO_2在PP和EPDM基体中较大的溶解度和溶胀度差异,在CO_2环境下退火处理PP/EPDM,可以显著增加EPDM相体积分数,进而促使EPDM相形貌从海-岛状结构向双连续结构转变。力学性能测试结果表明,在相同EPDM含量下,真空热退火后材料性能并没有发生显著变化,而经过CO_2退火后材料的储能模量和损耗模量均有提高,这意味着材料的刚性和韧性都得到提升。     

PP/EPDM/纳米TiO_2复合材料的性能研究

采用熔融共混法制备了聚丙烯(PP)/纳米二氧化钛(纳米TiO_2)/三元乙丙橡胶(EPDM)复合材料,分别研究了纳米TiO_2和EPDM的含量以及不同共混工艺对复合材料力学性能的影响,并对4种工艺制备的复合材料的形态结构进行分析。结果表明:固定纳米TiO_2含量为3%(wt,质量分数,下同),当EPDM的含量为10%时,PP/EPDM/纳米TiO_2三元复合材料的综合力学性能最好;固定EPDM含量为10%,当纳米TiO_2的含量为4%时,PP/EPDM/纳米TiO_2三元复合材料缺口冲击强度最高;二步法工艺均好于一步法工艺,4种工艺中制备得到"核壳"结构的复合材料韧性最好;纳米TiO_2粒子经两次共混分散性更好,有利于提高韧性。     

动态硫化EPDM/PP热塑性弹性体应力松弛的研究

从相态结构角度讨论动态硫化EPDM／PP共混物的应力松弛行为,并与纯PP以及静态硫化EPDM的应力松弛相比较,研究了制备工艺对动态硫化EPDM／PP共混物应力松弛的影响,结果表明,动态硫化EPDM／PP应力松弛主要由PP连续相决定的,EPDM分散相对共混物应力松弛有一定的影响。随橡塑化和软化剂用量的增加,EPDM／PP应力松弛明显降低,增大硫化剂用量,EPDM／PP应力松弛相对较小。     

聚丙烯/-1,2-聚丁二烯共混物的形态结构及性能

本文研究了乙烯基含量不同与分子量不同的1,,2-聚丁二烯(1,2-PB)与基聚丙烯(PP)共混物的形态结构和性能。结果表明,1,2-PB 与 PP 具有一定的相容性,相容程度与乙烯含基量有关。1,2-PB 的加入,使 PP 相邻球晶产生片层相互交叉的界面结构,又使 PP 有β型结晶生产。1.2-PB 的最隹增韧效果可与乙丙橡胶相比拟。     

α和β-成核作用硅灰石对聚丙烯结晶行为的共同作用

α/β复合成核剂改性聚丙烯(PP)已有研究,但α和β-成核作用无机粒子填充PP的结晶行为有待探索。文中通过制备α和β-成核作用硅灰石填充PP复合材料,考察了硅灰石所具有α和β-成核作用和成核效率对PP结晶行为、熔融特性和β-晶含量的影响及规律。结果表明,当2种硅灰石成核效率相差较大时,具有较高成核效率的硅灰石在PP成核结晶过程中发挥主导作用;而当2种硅灰石成核效率相近时,α和β-成核作用硅灰石之间存在竞争成核作用,最终形成β-晶含量由两者的质量比决定。     

Optically transparent ZnO-based n-i-p ultraviolet photodetectors

An optically transparent tin-doped indium oxide/ZnO/NiO n-i-p heterostructure photodiode was fabricated by ion beam assisted e-beam evaporation. The diode clearly demonstrates rectifying current-voltage (J-V) characteristics with a current rectification ratio up to 10⁴ at bias ± 2 V and a low reverse current of ∼ 100 nA/cm² at − 5 V. Analysis of J-V characteristics including time dependence of the dark current shows that the leakage current at low biases is attributed to thermal generation via defect states, and at high biases, field-enhanced carrier generation from the ZnO layer dominates. Spectral response and linearity measurements indicate that such a diode is particularly suitable for low level of ultraviolet detection.     

technical note Linear variable differential transformers — Practical hints

Some years ago, a requirement existed for the development of a transducer of the LVDT type having the greatest possible sensitivity and of the smallest possible size. It was developed by a purely intuitive process and resulted in a series of devices having a variety of practical applications. In particular, its use as an extensometer could be of interest in the field of strain measurement.     

Epitaxial growth and surface morphology of aluminum films deposited on mica studied by transmission electron microscopy and atomic force microscopy

The bulk structure and epitaxial growth of aluminum films deposited on mica substrates by thermal evaporation in a wide temperature range (16-550 °C) in high vacuum were investigated by transmission electron microscopy and transmission electron diffraction. The surface morphology of the films was observed and analyzed by atomic force microscopy. The films prepared at room temperature consist of single crystals having a diameter of 90 ± 40 nm with (111) planes. The surface of the films comprises spherical grains with morphology that is caused by self-shadowing during the deposition. The surface of the films becomes smoother as the temperature increases, and atomically-smooth surfaces with a root-mean-square roughness of about 0.45 nm over an area of 1 μm² are obtained at 250-350 °C. The crystals are oriented randomly along the [111] direction perpendicular to the substrate. The surface of the films consists of larger (> 300 nm) grains with terraces, and the surface becomes rough above 400 °C. Films with well-oriented single crystals along the [111] direction perpendicular to the substrate are obtained above 520 °C. The films grown epitaxially at 520-550 °C are characterized by the isolated grains with a diameter of 1220 ± 450 nm.     

Enhancement of the efficiency and the color stabilization in green organic light-emitting devices with multiple heterostructures acting as a hole transport layer

The electrical and the optical properties of organic light-emitting devices (OLEDs), with and without multiple heterostructures consisting of N, N-bis-(1-naphthyl)-N, N-diphenyl-1,1-biphenyl-4,4-diamine (NPB)/5,6,11,12-tetraphenylnaphthacene (rubrene) acting as a hole transport layer (HTL), were investigated. The OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures acting as an HTL showed the highest luminances and efficiencies. While the electroluminescence (EL) peak corresponding to the rubrene layer did not appear for the OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures, only the EL peak related to the tris (8-hydroxyquinoline) aluminum layer was observed. The Commission Internationale de l’Eclairage chromaticity coordinates of the OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures at 14 V were (0.321, 0.531), indicative of a deep stabilized green color.     

Fabrication and characterization of NiO/ZnO/ITO p-i-n heterostructure

Transparent oxide semiconductors (TOSs) are promising materials for a variety of optoelectronic applications such as UV detectors. While several TOS-based p-n and p-i-n diodes have been recently reported, the high reverse dark current still poses a major issue. In this work, we report on a NiO/ZnO/ITO p-i-n heterostructure with reduced dark current level suitable for practical applications. Ion beam-assisted e-beam evaporation was used to deposit both p-type NiO and intrinsic ZnO layers, while a conventional sputtering system was used to prepare the ITO layer. Samples with sputtered ZnO layer were also fabricated for comparison. The diodes demonstrated clear rectifying I-V characteristics with a current rectification ratio up to 10⁴ at bias voltages of ± 1 V. The lowest level of reverse dark current (∼ 10 nA/cm² at − 5 V) is observed in samples with ZnO deposited by ion beam-assisted e-beam evaporation. In comparison, diodes with sputtered ZnO layer show two orders of magnitude higher dark current. Analysis of the quasi-static J-V characteristics, including time dependence behavior, shows that the dark current can be attributed to thermal generation of charge carriers via deep defects states in the ZnO layer and charge injection from the contacts. Electrical and optical properties of the TOS films are presented and discussed along with deposition conditions and device performance.     

聚醚醚酮的结晶与熔融行为研究

研究了PEEK在高于熔点的温度范围内处理时的结晶行为以及结晶后的熔融行为。发现处理时熔融的PEEK将同时发生交联与结晶,交联使未结晶的部分结晶受阻,结晶使尚存的晶片增厚,从而导致PEEK在DSC上出现对应于不同晶体结构的新的熔融双峰,并在此基础上提出了处理过程中PEEK结构变化的模型。此外,还发现处理后的PEEK的熔点,可高于目前已报导的平衡熔点。     

The spectrum of cosmic-ray electrons measured with H.E.S.S.

The measurement of very-high-energy cosmic-ray electrons is intrinsically difficult due to the very steep electron spectrum with low fluxes and an enormous background of hadronic cosmic rays. The large collection areas needed for such a measurement can be provided by ground-based imaging atmospheric Cherenkov telescopes. The High Energy Stereoscopic System (H.E.S.S.) has performed the first ground-based cosmic-ray electron measurement and thereby extended the measured range of the spectrum to several TeV. Here the H.E.S.S. measurement is presented, as well as an extension of the H.E.S.S. spectrum towards lower energies. At these energies, H.E.S.S. can probe recent ATIC measurements, which have been interpreted in terms of dark matter scenarios.     

尼龙—6与羧基化改性LDPE共混体系的结构研究

通过密度测定、Molau实验、二甲苯萃取抽出物的IR分析,测定了尼龙-6与各种改性聚乙烯的结构,发现尼龙-6分子末端的胺基与MAH-g-LDPE的酸酐及离聚体的羧酸发生化学反应,生成的接枝物起到了共混体系增容剂的作用,改善了体系的亲合性。DSC测定表明,各种LDPE的加入均会使共混物中尼龙的结晶速率加快,Avrami指数上升。     

Enhancement of the lifetime in organic light-emitting devices fabricated utilizing wide-bandgap-impurity-doped emitting layers

The degradation behaviors of the electrical and the optical properties of organic light-emitting devices (OLEDs) fabricated with an emitting layer (EML) doped with or without a wide-bandgap-impurity were investigated. The OLEDs with a wide-bandgap-doped Alq₃ EML were more stable than those with an undoped Alq₃ EML. The existence of the doped wide-bandgap-impurity in the EML decreased the trap-charge density in the EML, resulting in an increase in the number of electrons in the Alq₃ EML. That increases in the number of electron in the Alq₃ EML for the OLEDs with a wide-bandgap-impurity decreased the staying time of the holes in the Alq₃ EML, resulting in an enhanced lifetime for the OLEDs. These results indicate that OLEDs with a wide-bandgap-impurity-doped EML hold promise for potential applications in long-lifetime OLED displays.     

电流变材料设计与制备研究进展

简述了电流变液的转变机理发展现状,重点阐述了电流变材料的设计、制备及性能研究进展,并对影响电流变效应的有关材料因素作了深入探讨。