A New Process to Make a Porous PTFE Structure from Aqueous PTFE Dispersion with the Help of Hydrogel

A novel method to make a porous material having relatively large cell diameter (200–300 m), which consisted of mainly poly(tetrafluoroethylene) (PTFE), was developed from aqueous PTFE dispersion by using the characteristics of hydrogel with the addition of carbon nanofiber (CNF). The porous material was produced as follows: firstly, an aqueous agar gel containing PTFE and CNF was prepared; secondly, the gel was freeze-dried; thirdly, the dried gel was heat-treated at 400°C where the agar was almost decomposed and PTFE became molten. The porous material showed electric conductivity (about 50 ), high porosity (about 96 vol%), and relatively uniform cell structures without shrinkage during freeze drying and heat treatment. While the method without CNF resulted in large shrinkage during heat treatment, meaning that CNF prevented the shrinkage. It was explained by the idea that the existence of rigid CNF, which was dispersed in the cell wall, prohibited the shrinkage of PTFE during heat treatment. It was unexpectedly found by SEM analysis that the porous materials had another macro-porous structure inside the cell wall, suggesting that the developed materials had a double porous structure.     

2—甲基—1，4—萘醌对DNA光敏损伤的诱导作用

选择波长337nm的激光作为激励光源，借助凝胶电泳研究了2－甲基－1，4－萘醌诱导的DNA光敏损伤。结果表明：在氧气饱和、脱氧条件下光敏损伤显著，DNA损伤主要与光子剂量、核酸与萘醌浓度比及DNA存在形式有关。     

火花点燃式发动机压缩比与数字计数器读数的校正关系

采用压缩比与数字计数器的对应检索校正关系来评定检查火花点燃式发动机的机械状况。根据沿海不同地区室内室间实验室的对比与协调试验计算分析，所采用的检索法达到美国沃克夏机器制造厂规定的ASTM精度。本文提出的检索法具有快速、简捷和准确等特点，可适用于沿海地区火花点燃式发动机的机械设备状况校准试验。     

Polylactide films formed by immersion precipitation: Effects of additives,nonsolvent, and temperature

The influence of nonsolvent, crystallinity of the polymer film, and addition of dodecane (a poor solvent for the polymer and for the nonsolvent) on the morphology of polylactides films has been investigated and was related to phase separation behavior. Both amorphous poly‐DL ‐lactide (PDLLA) and crystalline poly‐L ‐lactide (PLLA) were dissolved in dichloromethane, and subsequently films were made by immersion in nonsolvent baths. PDLLA gave dense films without any internal structure, since the structure was not solidified by crystallization or glassification. PLLA films show varying structure depending on the nonsolvent. With methanol, asymmetric morphologies were observed as a result from combined liquid‐liquid demixing and crystallization, while with water symmetric spherulitic structures were formed. As a next step, dodecane was added, which is not miscible with the nonsolvent, and we found it to have a strong influence on the morphology of the films. The PDLLA films with dodecane did not collapse: a closed cell structure was obtained. In PLLA films, dodecane speeds up phase separation and induces faster crystallization in the films, and the porosity, size of the pores, and interconnectivity increased. When the PLLA solutions were subjected to a heat pretreatment, crystallization could be postponed, which yielded a cellular structure around dodecane, which did not contain spherulites anymore. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 959–971, 2007     

Oxygen transport in ferrite-based ceramic membranes: Effects of alumina sintering aid

Moderate additions of Al₂O₃ to strontium ferrite-based mixed conductors, such as SrFe_0.7Al_0.3O_3−δ and La_0.2Sr_0.8Fe_0.8Ga_0.2O_3−δ with the composition close to the solid solution formation limits, make it possible to improve ceramics sinterability, to increase oxygen permeability and to decrease thermal expansion. These effects are associated with the segregation of alumina-rich phases, primarily SrAl₂O₄, and the formation of A-site cation-deficient perovskite. The improved properties of the SrFe_0.7Al_0.3O₃-based material were used to fabricate high-quality tubular membranes for methane conversion reactors. Similar enhancement in sinterability is also observed for another promising parent material of mixed-conducting membranes, La_0.5Sr_0.5FeO_3−δ. However, extensive dissolution of Al³⁺ cations in the iron sublattice, creation of A-site vacancies and changing the La:Sr concentration ratio all lead to decreasing ionic transport in La_0.5Sr_0.5FeO_3−δ. As a result, additions of either Al₂O₃ or SrAl₂O₄ have a deteriorating influence on the oxygen permeation fluxes through La_0.5Sr_0.5FeO₃-based ceramics.     

Some new operational modes and parameters of stress relaxation for the viscoelastic characterization of solid polymers. III. The area ratio mode and the intrinsic “strain–clock” function

The introduced area ratio mode of operation with its corresponding parameters seems to have a fairly high sensitivity to the viscoelastic response of the solid polymer. This appeared from the fact that a good distinction among the linear viscoelastic, the nonlinear viscoelastic, and the viscoplastic ranges of behavior can be made. By using a relevant rheological modeling and its corresponding algorithmical approach, in the case of isotactic polypropylene, this material can be characterized as a morphological three‐phase material consisting of an intraspherulitic crystalline, an amorphous phase, and a interspherulitic para‐crystalline phase. In this sense, the material was simulated using two models: the Poynting–Thomson and the Maxwell–Wierchert, from where a good response of the material to the first model appeared. The so‐called intrinsic “strain–clock” function and its corresponding coefficient of strength of nonlinear viscoelastic behavior, which were relieved by the experimental data, seem to be some powerful and very practical “tools” that can give a proven suplementary characterization of the material. Finally, by this intrinsic function, the existence of permanent internal stresses, was confirmed, in an indirect way, which was mentioned in part II of this study. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 149–158, 2003     

兰香草挥发油化学成分的研究

采用常压水蒸气蒸馏法提取了兰香草挥发油,得油率为 0.35 ~ 0.52%。其相对密度(20℃/4℃)0.9980 ~0.9900,折射率(20℃)1.4608,比旋光度+0.51°;酸值1.5。并用毛细管气相色谱、红外光谱、核磁共振谱和色-质联机等对该挥发油进行了系统的成分分析。在分出的112个色谱峰中,共鉴定出 71 个化合物,占挥发油总量的 94.6%。其主要成分为芳樟醇、紫苏醇、香芹酮、荠苎烯、4-甲基-6-庚烯-3-酮、葎草烯、马鞭草烯酮、左旋松香芹酮、2-壬烯-4-炔等。     

Ionic liquid mediated nano-composite polymer gel electrolyte for rechargeable battery application

ABSTRACT

Nano-composite polymer gel electrolytes (NPGEs) based on polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP, ionic liquid, 1-butyl-3- methylimidazolium bis(trifluoromethanesulfonyl)imide BMIMTFSI, Li-salt along with the addition of SiO₂ nanoparticles have been synthesized and characterized by various techniques. Prepared NPGEs show high room temperature ionic conductivity (~10^?3 S/cm) and have a wide electrochemical window (ECW) (~3.3–3.5 V). The galvanostatic charge/discharge profile was studied by sandwiching best performing NPGEs between a LiFePO₄ cathode and lithium metal anode. The specific discharge capacity of the cell (Li/NPGE/LiFePO₄) room temperature at 0.1C rate is found to be 138 mAh/g.     

Quantification of response time in poly(vinyl alcohol)–metal complex thermochromic polymeric systems

Thermochromic poly(vinyl alcohol) (PVA)‐based material was synthesized and an extensive study of its thermochromic behavior with respect to response time was carried out. It was observed that it is possible to manipulate the response time by keeping control over chemical and physical parameters. The response time, which is the most important property of a smart material, has in this case been found to be very much influenced by rate of heat transfer into the material. Different compositions of the thermochromic material and their corresponding response time with respect to rate of heat transfer were studied and correlated. First, a theoretical equation was derived and later on it was experimentally verified to quantify the response time in PVA–metal complex‐based thermochromic systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4832–4834, 2006     

Tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO4/SPEEK membranes

A study to evaluate the tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO₄/SPEEK composite membranes has been carried out. It is aimed to give an assessment of these materials for applications in proton exchange membrane fuel cells. The stress–strain response of the membranes was measured as a function of the degree of sulfonation (DS) and the filler–matrix ratio. In addition, the effects of immersion in water at various temperatures were explored in situ by means of a homemade testing chamber fitted to the tensile analyzer. The results indicate that the DS has an important influence on the final mechanical behavior of the membranes. The introduction of the BPO₄ solid filler leads to deterioration in mechanical performance compared to unfilled SPEEK. A general picture of the microstructural features influencing the mechanical properties of SPEEK and BPO₄/SPEEK membranes is proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2380–2393, 2005