一种桥链DOPO衍生物的合成及对聚乳酸的阻燃性能

以9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)和乙二醇为主要原料,碘化钠为催化剂,设计合成了一种新型的桥链DOPO衍生物(Di-DOPO)。采用红外光谱、差示扫描量热分析、热重分析、质谱分析、核磁共振等方法对其进行分析表征,确定了其结构。将该化合物与聚乳酸(PLA)共混,通过氧指数(LOI)测试、垂直燃烧、热重分析、锥形量热等手段考察了其对PLA的阻燃性能及热降解行为的影响。结果表明,Di-DOPO质量分数达到10%时就可以使阻燃PLA材料通过UL-94 V-0级,并能有效抑制PLA的熔滴现象,LOI值也由纯PLA的20%提升到36.3%。阻燃剂质量分数为5%,10%和15%时,热释放速率峰值(PHRR)分别降低了5.2%,12.7%,19.6%。当加入Di-DOPO后,阻燃PLA复合材料的热稳定性比纯PLA明显提高。综上,所制备的Di-DOPO阻燃剂对PLA具有很好的阻燃效果。     

涤纶的结构与性能在后加工过程中的变化

用ＷＡＸＤ法，ＤＳＣ法，密度法，声速法，ＹＧ－００１单纤维电子强力仪，研究了涤纶在后加工过程中结构和性能的变化，以及工艺条件对纤维结构和性能的影响。研究结果表明，涤纶的各结构参数在后加工过程中变化十分复杂，其结晶结构主要在二道牵伸工序形成，在紧张热定型工序结晶度最高。各工序温度对结晶度，晶粒尺寸等结构参数影响较大，尤其是二道牵伸温度直接影响纤维产品的结构和性能，因此，实际生产中，合理，准确地控制好     

Low temperature annealing of metals with electrical wind force effects

Conventional annealing is a slow, high temperature process that involves heating atoms uniformly, i.e., in both defective and crystalline regions. This study explores an electrical alternative for energy efficiency,where moderate current density is used to generate electron wind force that produces the same outcome as the thermal annealing process. We demonstrate this on a zirconium alloy using in-situ electron back scattered diffraction(EBSD) inside a scanning electron microscope(SEM) and juxtaposing the results with that from thermal annealing. Contrary to common belief that resistive heating is the dominant factor, we show that 5 × 10~4 A/cm~2 current density can anneal the material in less than 15 min at only135?C. The resulting microstructure is essentially the same as that obtained with 600?C processing for360 min. We propose that unlike temperature, the electron wind force specifically targets the defective regions, which leads to unprecedented time and energy efficiency. This hypothesis was investigated with molecular dynamics simulation that implements mechanical equivalent of electron wind force to provide the atomistic insights on defect annihilation and grain growth.     

聚乳酸/蒙脱土纳米复合材料的冷结晶及熔融行为

采用熔融插层法制备了插层型的聚乳酸/蒙脱土纳米复合材料(PLA/MMTs)。利用差示扫描量热仪(DSC)和X射线衍射(XRD)对该纳米复合材料的结晶及熔融行为进行了研究。结果表明,PLA/MMTs复合体系不能从熔体冷却结晶,但可在较慢的升温过程中固态下冷结晶;蒙脱土不会改变PLA基体结晶的α晶型,但具有异相成核作用,促进了PLA基体的冷结晶在更低的温度下进行;复合体系在较慢升温速率下的双重熔融现象源于原始晶粒熔融重结晶行为。     

Probing the thermal decomposition behaviors of ultrathin HfO2 films by an in situ high temperature scanning tunneling microscope

The thermal decomposition of ultrathin HfO(2) films (～0.6-1.2?nm) on Si by ultrahigh vacuum annealing (25-800?°C) is investigated in?situ in real time by scanning tunneling microscopy. Two distinct thickness-dependent decomposition behaviors are observed. When the HfO(2) thickness is ～ 0.6?nm, no discernible morphological changes are found below ～ 700?°C. Then an abrupt reaction occurs at 750?°C with crystalline hafnium silicide nanostructures formed instantaneously. However, when the thickness is about 1.2?nm, the decomposition proceeds gradually with the creation and growth of two-dimensional voids at 800?°C. The observed thickness-dependent behavior is closely related to the SiO desorption, which is believed to be the rate-limiting step of the decomposition process.     

The influence of the fiber drawing process on intrinsic stress and the resulting birefringence optimization of PM fibers

The propagation properties of optical fibers can be significantly influenced by intrinsic stress. These effects are often undesired but in some cases essential for certain applications, e.g. in polarization maintaining (PM) fibers. In this paper, we present systematic studies on the influence of the fiber drawing process on the generated stress and demonstrate an approach to significantly increase the stress induced birefringence of PM-fibers. It is shown that the thermal stress caused by the material composition is superimposed with the mechanical stress caused by the fiber fabrication process. This intrinsic stress has a strong effect on the optical and mechanical properties of the glass and thus influences the fiber stability and modal behavior. By applying a thermal annealing step, the mechanical stress due to the fiber drawing process can be canceled. It is shown that this annealing step compensates the stress reducing influence of the drawing process on the birefringence of PM-fibers with panda structure. The comparison of the intrinsic stress states after fabrication with the state after the additional high temperature annealing step clearly shows that it is possible to improve the overall birefringence of panda fibers using appropriate preparation steps.     

Poly(lactic acid)/graphene nanocomposites prepared via solution blending using chloroform as a mutual solvent

Poly(lactic acid) (PLA)/graphene nanocomposites were prepared by direct solution blending of PLA with graphene using chloroform as a mutual solvent. Graphene was prepared by a solution-phase processing followed by thermal reduction, which can be dispersed stably in chloroform for more than one month. Transmission electron microscopy (TEM) was used to examine the quality of the dispersion of graphene in the PLA matrix. The thermal properties and crystallization behavior of the nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and polar optical microscopy (POM). The results showed that the thermal stability of PLA was significantly improved with a very low loading of graphene and the addition of graphene had a great effect on spherulite morphology of PLA.     

凹凸棒黏土对聚乳酸结晶性能和热稳定性能的影响

采用熔融共混法分别制备了凹凸棒黏土质量分数为1%、 3%和5%的纳米凹凸棒黏土(ATT)/聚乳酸(PLA)复合材料, 研究了ATT对PLA结晶性能和热稳定性能的影响。结果表明, ATT与PLA基体具有较好的相容性, 当ATT含量低于3%时, 可以均匀的分散在PLA基体中, 而达到5%时则会发生团聚。FTIR结果表明, ATT与PLA基体之间存在较强的相互作用。ATT可明显促进PLA的结晶, 起到异相成核的作用。ATT纳米颗粒的添加引起了PLA冷结晶峰向低温方向移动, 使冷结晶温度从114.4 ℃降低至103 ℃左右。含ATT体系结晶速率比纯PLA快, 表明ATT的加入可以促进PLA的结晶, 说明ATT是PLA有效的成核剂之一。添加ATT可明显加快PLA的结晶速率并减小球晶尺寸。当添加3%ATT时, ATT/PLA复合材料的热分解温度比纯PLA提高了11 ℃, 这主要是由于ATT/PLA网络密度的提高, 使ATT在PLA的降解过程中能够起到较好的阻隔作用, 抑制了PLA的降解自加速过程。     

甘蔗渣的改性方法对甘蔗渣/聚乳酸复合材料结构与性能的影响

采用碱处理、硅烷偶联剂及碱处理后再硅烷偶联剂等方法改性甘蔗渣（BF）,将改性后的BF与聚乳酸（PLA）共混制备BF/PLA复合材料。采用TGA、FTIR和SEM分析研究BF/PLA复合材料的热稳定性;分别采用Flynn-Wall-Ozawa（FWO）法和Kissinger法研究BF/PLA复合材料的热分解动力学。结果表明,BF/PLA复合材料的热稳定与BF的结构及BF/PLA复合材料的界面相容性有关。碱处理使BF原纤化,降低BF的耐热性,不利于BF/PLA复合材料热稳定性及力学性能的提高;硅烷偶联剂改性可以改善BF与PLA的界面相容性,有助于提高BF/PLA复合材料的热稳定性。FWO法与Kissinger法计算得到的热分解活化能较一致,说明这两种方法都适合研究BF/PLA复合材料的热分解动力学。在所对比的BF/PLA复合体系中,硅烷偶联剂改性的BF/PLA复合材料热分解活化能最高、力学性能最佳,碱处理后再硅烷偶联剂改性的BF/PLA复合材料次之。     

成核剂TMC-328对可生物降解聚乳酸结晶性能的影响

用熔融法制备了含成核剂TMC-328质量分数分别为0、0.1%、0.2%、0.3%的聚乳酸(PLA)/TMC-328共混物,采用偏光显微镜(POM)、差示扫描量热仪(DSC)及扫描电子显微镜(SEM),研究了PLA共混物的结晶性能、热性能和内部形貌。结果表明,TMC-328对PLA结晶性能的影响体现在PLA的冷结晶过程上,并且最佳添加量为0.1%,相对应的冷结晶温度(Tcc)从126.14℃降到111.40℃,冷结晶焓(ΔHcc)从11.34J/g增加到23.49J/g,在100℃下完全结晶的时间为22min左右,SEM照片显示TMC-328的团聚现象随着含量的增加变得很明显。     

氧化增强注氧隔离工艺制备绝缘体上的硅锗

提出一种氧化增强注氧隔离工艺,在退火前氧化得到SiO2层,再进行高温退火得到绝缘体上的硅锗材料.经X射线摇摆曲线和拉曼测试发现所制备的绝缘体上的SiGe材料锗含量没有发生损失,且应变弛豫完全.透射电镜和二次离子质谱分析结果显示样品多层结构清晰,埋氧层质量完好、平整度高、无不连续、无硅岛.研究表明,氧化增加工艺的引入是绝缘体上的硅锗材料锗质量提高的关键.     

Small angles X-ray diffraction and Mössbauer characterization of annealed Tb/Fe multilayer

The effect of thermal annealing on the structure and magnetic properties of crystalline Tb/Fe multilayers has been studied using conversion electron M?ssbauer spectrometry and small-angle X-ray diffraction. The growth of Tb–Fe amorphous alloy from the interface is observed with increasing annealing temperature. After annealing at 873 K, a clear total mixing of the multilayers by interdiffusion has been evidenced. The results are compared with the effect of ion irradiation in the same system.     

Solution-processed nanocrystalline TiO2 buffer layer used for improving the performance of organic photovoltaics

In this study, we use solution-processable crystalline TiO(2) nanoparticles as a buffer layer between the active layer and aluminum cathode to fabricate the P3HT:PCBM-based bulk heterojunction (BHJ) organic photovoltaic (OPV) devices. The employment of the presynthesized TiO(2) nanoparticles simplifies the fabrication of OPV devices because of the elimination of an additional hydrolysis step of precursors in air. The fabricated OPV devices with the thermally stable TiO(2) buffer layer are subjected to the further postdeposition thermal annealing, resulting in a power conversion efficiency (PCE) as high as 3.94%. The improved device performance could be attributed to the electron transporting and hole blocking capabilities due to the introduced TiO(2) buffer layer.     

Effect of the initial structure on the electrical property of crystalline silicon films deposited on glass by hot-wire chemical vapor deposition

Crystalline silicon films on an inexpensive glass substrate are currently prepared by depositing an amorphous silicon film and then crystallizing it by excimer laser annealing, rapid thermal annealing, or metal-induced crystallization because crystalline silicon films cannot be directly deposited on glass at a low temperature. It was recently shown that by adding HCI gas in the hot-wire chemical vapor deposition (HWCVD) process, the crystalline silicon film can be directly deposited on a glass substrate without additional annealing. The electrical properties of silicon films prepared using a gas mixture of SiH4 and HCl in the HWCVD process could be further improved by controlling the initial structure, which was achieved by adjusting the delay time in deposition. The size of the silicon particles in the initial structure increased with increasing delay time, which increased the mobility and decreased the resistivity of the deposited films. The 0 and 5 min delay times produced the silicon particle sizes of approximately 10 and approximately 28 nm, respectively, in the initial microstructure, which produced the final films, after deposition for 300 sec, of resistivities of 0.32 and 0.13 Omega-cm, mobilities of 1.06 and 1.48 cm2 V(-1) S(-1), and relative densities of 0.87 and 0.92, respectively.     

Crystallization and thermochromism in tungsten oxide films annealed in vacuum

The crystalline phases formed in tungsten oxide (WO_{3 ? x} ) films upon isothermal step annealing in vacuum and air at various temperatures within 500?C750°C have been studied. The films were deposited onto silica glass substrates by reactive dc magnetron sputtering. It is established that the observed thermochromism is related to the presence of an oxygen-deficient WO_{3 ? x} phase belonging to the hexagonal system, which is intensely formed as the annealing temperature increases from 650 to 750°C.     

Synthesis and characterization of novel biodegradable pentablock copolymers from L‐lactide,p‐dioxanone and poly (ethylene glycol)

ABCBA type pentablock copolymers, in which the A, B and C blocks are poly (p‐Dioxanone) (PPDO), poly (L‐Lactide) (PLLA), and polyethylene glycol (PEG), respectively, were synthesized via a two‐step ring‐opening polymerization in bulk using stannous octoate as the catalyst. PLA‐b‐PEG‐b‐PLA Triblock copolymer was synthesized at first and then p‐Dioxanone monomers as the other blocks were added to it. In the first step, poly ethylene glycol and, in the second step, triblock copolymer acts as the macro initiator. The obtained copolymers were identified by ?1&/sup;H&/I;, ?13&/sup;CNMR&/I; and IR&/I; spectroscopy. The intrinsic viscosity of copolymers was measured in chloroform/phenol (3/1 v/w) solution. The thermal properties, such as melting point, melting enthalpy and crystallinity, were studied. From the results of differential scanning calorimetry and thermal gravimetric analysis, it was observed that the PPDO blocks show similar crystallization behavior like homopolymer and also melting temperature of two PPDO end blocks raise with an increase in DON content in copolymer.     

Epitaxial growth and thermal stability of silicon layers on crystalline gadolinium oxide

In this work, an unconventional approach for epitaxial growth of Si on single-crystalline rare-earth oxide is presented using molecular beam epitaxy under ultra-high vacuum. Surface and bulk crystalline structures as well as chemical content were examined. Silicon-on-insulator layers were fabricated by encapsulated solid phase epitaxy on Si(111) substrate. The gadolinium oxide capping layer was removed by wet-chemical etching. The remaining silicon layer is single crystalline without any impurities and exhibits 7 × 7 reconstructed surface after annealing in very low silicon flux in the growth chamber. The thermal stability of the fabricated silicon-on-insulator structure was studied by step-wise heating under ultra-high vacuum conditions. The fabricated ultra-thin (10-15 nm) silicon-on-oxide layers remain structurally and chemically stable up to 900 °C.     

Densification of sol–gel TiO2 very thin films studied by SPR measurements

Very thin TiO₂ films have been prepared by sol–gel and deposited on a silver layer for Surface Plasmon Resonance (SPR) measurements. Densification of the samples has been studied by determining from SPR measurements the optical index (ranging from 1.68 to 1.92) and thickness (ranging from 6 to 2 nm) at each step of the annealing procedure. The structure of the layer (amorphous and/or crystalline) has been checked at the final stage of the thermal treatment by High Resolution Transmission Electron Microscopy (HRTEM).     

纤维表面改性对PLA/Flax复合材料性能的影响

目的研究纤维表面改性对复合材料结晶、热稳定性、动态力学性能、尺寸稳定性、吸水率等的影响。方法采用碱、碱+马来酸酐、碱+KH550这3种处理方法对纤维表面进行改性,通过熔融挤出与聚乳酸(PLA)混合制备聚乳酸/亚麻纤维(PLA/Flax)复合材料。结果亚麻纤维经表面改性后使PLA更容易发生冷结晶,结晶结构更加致密、完善,PLA/Flax尺寸稳定性优于PLA。纤维的加入提高了PLA的吸水率,但热稳定性能有所降低。纤维表面改性降低了PLA/Flax的储能模量。结论碱+KH550处理纤维与PLA共混所得复合材料的结晶性、尺寸稳定性最佳,为高性能PLA/Flax复合材料的制备提供了一定的实验及理论依据。     

Solution blow spinning: parameters optimization and effects on the properties of nanofibers from poly(lactic acid)/dimethyl carbonate solutions

Solution blow spinning (SBS) is a process to produce non-woven fiber sheets with high porosity and an extremely large amount of surface area. In this study, a Box–Behnken experimental design (BBD) was used to optimize the processing parameters for the production of nanofibers from polymer solutions consisting of poly(lactic acid) (PLA) dissolved in dimethyl carbonate. In addition, a comparative study between SBS fibers and cast film was performed to verify the influence of the SBS process on the crystallinity and thermal properties of PLA. The PLA concentration in polymer solutions was the most significant parameter affecting fiber diameter. The BBD analysis revealed that small diameter fibers were best obtained by a combination of 8 % w/v PLA concentration, 80 psi air pressure, and a feed rate of 50 µL min^?1. The comparative study showed that both the SBS and the film casting processes increased the PLA crystallinity. However, the PLA films had a higher degree of crystallinity compared with the fibers made by the SBS process (39 and 17 %, respectively), which was attributed to the high shear created at the SBS nozzle inducing orientation and chain alignment. During the fiber formation, crystals formed with varied morphology including the α′-crystals, which have a less ordered structure and lower thermal stability compared to the α-crystals. The lower thermal stability of SBS fibers compared to the films can be explained by the lower degree of crystallinity and also by the higher surface area which can accelerate the weight loss process.