Surface characterization of cross-linked elastomers by shear modulation force microscopy

Brominated poly(isobutylene-co-4-methylstyrene) (BIMS) is a synthetic terpolymer which can be stoichiometrically cross-linked by N,N′-dicinnamylidene-1,6-hexanediamine (DIAK). The degree of cross-links on bulk samples was determined by measuring the low frequency shear modulus with parallel plate method. The surface modulus of the same samples was measured using a new method, shear modulation force microscopy (SMFM). The moduli of the bulk sample and the surface were found to have the same scaling with the cross-link density, and good agreement with rubber elasticity theory was obtained in both cases. The SMFM was then used to monitor the cross-linking process, as a function of DIAK concentration and curing time, in thin films where standard rheological methods cannot be applied. The results show that in all cases the cross-linking reaction at the surface reaches saturation in less than 10 min as compared to at least 1 h in the bulk samples.     

Electrodeposition of smooth and adherent film of polypyrrole on lead electrode

Electropolymerization of pyrrole on lead substrate electrode was studied. Due to electrochemical activity of Pb in acidic media, this process is only possible at basic pHs. For this purpose, electropolymerization process was performed in an aqueous solution of Na₂SO₄ with pH 12. Potentiodynamic cycling shows the Pb oxidation at the first cycles. In subsequent cycles, polypyrrole film grows on the oxidized lead substrate. Of course, as the passive film is highly porous, a composite of polypyrrole/PbSO₄ is formed in the first layers. However, subsequent cycling leads to the formation of pure polypyrrole film. According to this structure and strong connection of the polymer film to the substrate surface via this composite layer, the polypyrrole film deposited on the lead surface has enhanced mechanical stability. AFM measurements showed peculiar smoothness of both composite and lateral polypyrrole films. This synthesis approach is of particular interest for the preparation of highly stable polymer films and fabrication of supercapacitors with a polymer/PbSO₄ conductive structure.     

Novel high strength graphitic foams

A novel high strength graphitic foam was produced through the incorporation of carbon nanofibers into a pitch based precursor. The nanofiber reinforced cellular foams were mechanically tested both from a localized and bulk perspective with results indicating enhanced foam performance with nanofiber addition. The magnitude of increased performance was a result of both the nanofiber itself as well as its heat treatment as an increase in each was found to cause an associated increase in foam performance. The increase in mechanical capability is attributed to the formation of a zigzag structure in the ligaments and nodes of the foam. This zigzag structure serves as an interlocking mechanism, preventing easy shearing of the graphene layers. The in situ fracture mechanics experiment shows brittle behavior of a single ligament indicating that only reinforced foam behaves like that of a carbon fiber.     

Effect of carbon fiber surface functional groups on the mechanical properties of carbon-carbon composites with HTT

The present investigation describes the quantitative measurement of surface functional groups present on commercially available different PAN based carbon fibers, their effect on the development of interface with resol-type phenol formaldehyde resin matrix and its effect on the physico-mechanical properties of carbon-carbon composites at various stages of heat treatment. An ESCA study of the carbon fibers has revealed that high strength (ST-3) carbon fibers possess almost 10% reactive functional groups as compared to 5.5 and 4.5% in case of intermediate modulus (IM-500) and high modulus (HM-45) carbon fibers, respectively. As a result, ST-3 carbon fibers are in a position to make strong interactions with phenolic resin matrix and HM-45 carbon fibers make weak interactions, while IM-500 carbon fibers make intermediate interactions. This observation is also confirmed from the pyrolysis data (volume shrinkage) of the composites. Bulk density and kerosene density more or less increase in all the composites with heat treatment up to 2600 °C. It is further observed that bulk density is minimum and kerosene density is maximum upon heat treatment at 2600 °C in case of ST-3 based composites compared to HM-45 and IM-500 composites. It has been found for the first time that the deflection temperature (temperature at which the properties of the material start to decrease or increase) of flexural strength as well as interlaminar shear strength is different for the three composites (A, B and C) and is determined by the severity of interactions established at the polymer stage. Above this temperature, flexural strength and interlaminar shear strength increase in all the composites up to 2600 °C. The maximum value of flexural strength at 2600 °C is obtained for HM-45 composites and that of ILSS for ST-3 composites.     

几种光谱方法(FTIR、FT-Raman,NMR)在橡胶分析中的应用

综述了傅里叶变换红外光谱 ,傅里叶变换拉曼光谱以及核磁共振波谱在橡胶结构的定性、定量分析中的应用     

Exploring the effect of dry premixing of sand and cement on the mechanical properties of mortar

A spout-fluid bed device was developed for dry premixing sand and cement to produce mortar. The goal of the work was to explore the efficacy of a new method for dispersing cement in sand to produce a mortar with better mechanical and physical properties. This strategy was found to work best at high sand/cement ratios, indicating that the dry premixing is more effective as the cement content is reduced and that it may be possible to produce commercially acceptable mortars with a lower cement content. Other properties of the mortar are also positively affected, including a decrease in the shrinkage and an increase in the workability.     

用固体核磁技术分析PE 100管材料的抗熔垂性

用固体核磁技术分析了2种具有不同抗熔垂性能的聚乙烯管材料的凝聚态结构与流变性能。管材树脂的抗熔垂性能与其核磁迟豫特性紧密相关,好的抗熔垂性能对应更长的纵向迟豫时间。抗熔垂性能好的双峰管材料的重均分子量更高,高相对分子质量部分的含量更多。     

Synthesis and characterization of soluble (porphyrinato)iron(II) polymers

The use of (tetrakis(4-hexylphenyl)porphyrinato)Fe(II) in polymerization reactions with bidentate ligands such as 9,10-diisocyanoanthracene and 1,4-diisocyanobenzene led to well-defined stacked polymers1 and2 which are still soluble in common organic solvents such as chloroform, dichloromethane, and tetrahydrofurane. They have been completely characterized by¹H-NMR and UV/vis spectropscopy in solution, even allowing end-group analysis for determination of the average degree of polymerization, yieldingn=10 andn=5 for1 and2, respectively. Mößbauer and IR spectroscopy further established the strong Fe-CN bonding reflected by very small isomer shifts and quadrupole splittings (E _Q0.2 mm s^–1) and a large decrease in the IR stretching frequency (v _CN60 cm^–1). The axially stacked polymers exhibit semiconducting properties only upon doping.Presented at the 5th International Symposium on Macromolecule-Metal Complexes (MMV), Summer 1993 in Bremen, Germany.     

热塑型聚氨酯复合体系力学性能研究

采用压延机，在加工温度不高于１２０°Ｃ的条件下，成功地制备出热塑型聚氨酯弹性体（ＴＰＵ）与高氯酸铵、铝粉及增塑剂邻苯二甲酸二丁酯（ＤＢＰ）等组成的复合胶片，拉伸实验结果指出了所制备的热塑性弹性体复合体系具有良好的力学性能，完全达到或超过推进剂体系的要求指标。     

Surface plasmon resonance evaluation of various aminoglycoside-RNA hairpin interactions reveals low degree of selectivity

Aminoglycoside antibiotics, which are able to selectively bind to RNA, are considered to be an important lead in RNA-targeting drug discovery. In this study, surface plasmon resonance (SPR) was employed to explore the interaction of aminoglycosides with known tobramycin-binding RNA hairpins (aptamers) and an unrelated RNA hairpin. It was established that aminoglycosides have multiple interactions with RNA hairpins. Unexpectedly, the different hairpins showed comparable affinity for a set of related aminoglycosides. The observed absence of selectivity presents an extra hurdle in the discovery of novel aminoglycosides as specific drugs that target defined RNA hairpins.