Reversible tuning of the wettability of carbon nanotube arrays: the effect of ultraviolet/ozone and vacuum pyrolysis treatments.

Among diverse types of synthetic materials, arrays of vertically aligned carbon nanotubes have attracted the most attention, mainly because of their exceptional mechanical, electrical, optical, and thermal properties. However, their wetting properties are yet to be understood. In this present study, oxygenated surface functional groups have been identified as a vital factor in controlling the wetting properties of carbon nanotube arrays. The results presented herein indeed show that a combination of ultraviolet/ozone and vacuum pyrolysis treatments can be used to vary the surface concentration of these functional groups such that the carbon nanotube array can be repeatedly switched between hydrophilic and hydrophobic.

Friction between carbon fibre reinforced polymers: Experiments and modelling

Carbon fibre reinforced polymers (CFRP) are well-known for the excellent combination of mechanical and thermal properties with light weight. However, their tribological properties are still largely uncovered. In this work an experimental study of friction between two CFRP at weak normal load (inferior to 20 N) was performed. Two effects were scrutinuously studied during the experiments: fibre volume friction and fibre orientation. In addition to this experimental work, a modelling of a contact between two FRP was realized. It is supposed that the real area of contact consists of a multitude of microcontacts of three types: fibre-fibre, fibre-matrix and matrix-matrix. The experimental work has shown a small rise in friction coefficient with the change of fibre orientation of two composites from parallel to perpendicular relative to the sliding direction. In parallel, the proposed analytical model predicts a independence of this angle. Regarding the influence of the fibre volume fraction, Vf, the experiments reveal a decrease in friction coefficient of 50% with a change of Vf from 0% to 62%. This observation corresponds to the qualitative dependence depicted with the model. © 2012 EDP Sciences.

Studies of 6H-SiC devices

Silicon carbide (SiC) is recently receiving increased attention due to its unique electrical and thermal properties. It has been regarded as the most appropriate semiconductor material for high power, high frequency, high temperature, and radiation hard microelectronic devices. The fabrication processes and characterization of basic device on 6H-SiC were systematically studied. The main works are summarized as follows:The homoepitaxial growth on the commercially available single-crystal 6H-SiC wafers was performed in a modified gas source molecular beam epitaxy system. The mesa structured p(+)n junction diodes on the material were fabricated and characterized. The diodes showed a high breakdown voltage of 800 V at room temperature. They operated with good rectification characteristics from room temperature to 673 K.Using thermal evaporation, Ti/6H-SiC Schottky barrier diodes were fabricated. They showed good rectification characteristics from room temperature to 473 K. Using neon implantation to form the edge termination, the breakdown voltage was improved to be 800 V.n-Type 6H-SiC MOS capacitors were fabricated and characterized. Under the same growing conditions, the quality of polysilicon gate capacitors was better than Al. In addition, SiC MOS capacitors had good tolerance to gamma rays. (C) 2002 Published by Elsevier Science B.V.

Studies of 6H-SiC devices

Silicon carbide (SiC) is recently receiving increased attention due to its unique electrical and thermal properties. It has been regarded as the most appropriate semiconductor material for high power, high frequency, high temperature, and radiation hard microelectronic devices. The fabrication processes and characterization of basic device on 6H-SiC were systematically studied. The main works are summarized as follows:The homoepitaxial growth on the commercially available single-crystal 6H-SiC wafers was performed in a modified gas source molecular beam epitaxy system. The mesa structured p(+)n junction diodes on the material were fabricated and characterized. The diodes showed a high breakdown voltage of 800 V at room temperature. They operated with good rectification characteristics from room temperature to 673 K.Using thermal evaporation, Ti/6H-SiC Schottky barrier diodes were fabricated. They showed good rectification characteristics from room temperature to 473 K. Using neon implantation to form the edge termination, the breakdown voltage was improved to be 800 V.n-Type 6H-SiC MOS capacitors were fabricated and characterized. Under the same growing conditions, the quality of polysilicon gate capacitors was better than Al. In addition, SiC MOS capacitors had good tolerance to gamma rays. (C) 2002 Published by Elsevier Science B.V.

基于紧束缚分子动力学模型的Na4,Na8和Na20团簇结构及热力学性质研究

利用距离相关的紧束缚的分子动力学模型（DDTB－MD），通过提取不同温度下的势能、构型、无单位键长涨落平均位移、扩散系数、围绕质心的径向分布等参量，系统的研究了菱形结构和T形结构的Na4、Td结构和D2d结构的Na8，以及Na20的热力学的性质。对于Na4，比较了金属团簇Na4的菱形结构和T形结构两种异构体之间热力学性质的异同。发现在团簇温度升高的过程中，两种异构体都会发生从类固到类液的相变。T形结构的Na4熔点要比菱形结构的低。在相变的过程中都会发生赝转动和异构化。还发现了赝转动的判据不仅仅只是温度，还包括无单位键长涨落的δ值。菱形结构的Na4在200K左右不一定会发生赝转动，只有观察到温度处于200K左右，δ值≥0.08的时候，赝转动则必然会观察到。菱形结构Na4的赝转动过程中会发现T形结构的异构化，但其维持时间很短，不稳定，很快又转变为菱形结构。而T形结构在170K就能观察到异构化和赝转动的发生，在这个温度下会不断的在菱形与T型之间发生异构，而处于菱形结构的时间要比T型长的多。表现为菱形结构的稳定性要大于T型。对于Na8的两种不同的异构体（分别为Td结构和D2d结构），发现尽管两个异构体的基态能量很接近，但他们的稳定性、熔化过程的热力学性质等有着很大的差别，这也反映了它们在几何结构上的差别。对称性强的Td结构更紧密，在熔化过程中表现出更高的稳定性，具有较高的熔点，具有类晶体的性质.对称性弱的D2d结构则具有较低的熔点，很宽的熔化温度范围，具有类似非晶体的性质. 再比较了基态结构下的Na8和Na20。通过提取对不同的子系统在不同温度下的无单位键长涨落等参数，发现金属原子团簇Na20在熔化过程中表现出了并不像通常金属团簇那样的表面先熔化，而是从内部开始先熔化的奇异特性

Microencapsulation of n-hexadecane as a phase change material in polyurea

For thermal energy storage application, polyurea microcapsules about 2.5 mum in diameter containing phase change material were prepared using interfacial polycondensation method. In the system droplets in microns are first formed by emulsifying an organic phase consisting of a core material ( n-hexadecane) and an oil-soluble reactive monomer, toluene-2, 4-diisocyanate (TDI), in an aqueous phase. By adding water-soluble reactive monomer, diamine, monomers TDI and diamine react with each other at the interface of micelles to become a shell. Ethylenediamine (EDA), 1, 6-hexane diamine (HDA) and their mixture were employed as water-soluble reactive monomers. The effects of diamine type on chemical structure and thermal properties of the microcapsules were investigated by FT-IR and thermal analysis respectively. The infrared spectra indicate that polyurea microcapsules have been successfully synthesized; all the TG thermographs show microcapsules containing n-hexadecane can sustain high temperature about 300 degreesC without broken and the DSC measurements display that all samples possess a moderate heat of phase transition; thermal cyclic tests show that the encapsulated paraffin kept its energy storage capacity even after 50 cycles of operation. The results obtained from experiments show that the encapsulated n-hexadecane possesses a good potential as a thermal energy storage material.

TDR研制与应用方面的若干进展

通过分析近年来国内外关于TDR的文献,总结了TDR研制与应用方面的若干新进展,概括了在使用TDR时应注意的几个问题。结果表明,线圈型TDR探针可很好地解决TDR探针在物理长度上的限制;多功能TDR探针可用来同时测定含水量与基质势、含水量与土壤热学性质、含水量与盐度和温度。当温度在5～45℃之间变化时随着温度的升高,TDR在沙壤土中测定的土壤含水量降低,而在粘壤土和有机质含量高的土壤测定的土壤含水量值升高。TDR探针应以合适的角度插入土壤,同时尽量避免摇摆、两探针不平行插入等误操作。

Syntheses of opened hollow clay microspheres through a spray-drying approach and their derivative clay/carbon nanotubes composites

Opened hollow microspheres of organoclays were prepared via spray drying the suspension of modified Na+-montmorillonite (Na+-MMT) with alkylsulfonate. The microstructure and thermal properties of these opened hollow spheres were characterized by means of wide-angle X-ray diffraction, field emission scanning electron microscopy, and thermogravimetric analysis. The results showed that the organoclays had larger interlayer spacing compared with pure Na+-MMT and higher thermal stability relative to the alkylsufonate.

Blends of Poly(lactic acid) with Thermoplastic Acetylated Starch

Blends of poly(lactic acid)(PLA) and thermoplastic acetylated starch(ATPS) were prepared by means of the melt mixing method. The results show that PLA and ATPS were partially miscible, which was confirmed with the measurement of T-g by dynamic mechanical analysis(DMA) and differrential scanning calorimetry(DSC). The mechanical and thermal properties of the blends were improved. With increasing the ATPs content, the elongation at break and impact strength were increased. The elongation at break increased from 5% of neat PLA to 25% of the blend PLA/ATPS40. It was found that the cold crystallization behavior of PLA changed evidently by addition of ATPS. The cold crystallization temperature(T-cc) of each of PLA/ATPS blends was found to shift to a lower temperature and the width of exothermic peak became narrow compared with that of neat PLA.

Sulphonated Tetramethyl Poly(ether ether ketone)/Epoxy/Sulphonated Phenol Novolac Semi-IPN Membranes for Direct Methanol Fuel Cells

The sulphonated phenol novolac (PNBS) which was used as a curing agent of epoxy was synthesised from phenol novolac (PN) and 1,4-butane sultone and confirmed by FTIR and H-1 NMR. The degree of sulphonation (DS) in PNBS was calculated by H-1 NMR. The semi-IPN membranes composed of sulphonated tetramethyl poly(ether ether ketone) (STMPEEK) (the value of ion exchange capacity is 2.01 meq g(-1)), epoxy (TMBP) and PNBS were successfully prepared. The semi-IPN membranes showed high thermal properties which were measured by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) With the introduction of the corss-linked TMBP/PNBS, the mechanical properties, dimensional stability, methanol resistance and oxidative stability of the membranes were improve in comparison to the pristine STMPEEK membrane.

Preparation and Characterization of Melt Grafting 2-acrylamido-2-methyl-1-propanesulfonic Acid onto Pre-Irradiated Linear Low Density Polyethylene

Linear low density polyethylene (LLDPE) was functionalized with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) by using -ray pre-irradiation in air in a twin-screw extruder. Fourier-transformed infrared spectroscopy (FT-IR) and electron spectroscopy for chemical analysis (ESCA) were used to characterize the formation of LLDPE-g-AMPS copolymers. The content of AMPS in LLDPE-g-AMPS was determined by using element analysis instrument. The effects of concentrations of monomer, reaction temperature and pre-irradiation dose on degree of grafting were investigated. The critical surface tension of LLDPE-g-AMPS was measured by using contact angle method. The influences of the degree of grafting on crystallization properties were studied by using DSC. Compared with neat LLDPE, the crystallization temperature increased about 4C, and crystallinity decreased with increasing degree of grafting. Crystallization rates of grafted LLDPE were faster than that of plain LLDPE at the same crystallization temperature.

Naphthyl and thionaphthyl end-capped oligothiophenes as organic semiconductors: Effect of chain length and end-capping groups

Two series of oligothiophenes (OThs), NaTn and TNTn (n = 2-6 represents the number of thiophene rings), end-capped with naphthyl and thionaphthyl units have been synthesized by means of Stille coupling. Their thermal properties, optical properties, single crystal structures, and organic field-effect transistor performance have been characterized. All oligomers display great thermal stability and crystallinity. ne crystallographic structures of NaT2, NaT3, TNT2, and TNT3 have been determined. The crystals of NaT2 and NaT3 are monoclinic with space group P2(1)/C, while those of TNT2 and TNT3 are triclinic and orthorhombic with space groups P-1(-) and P2(1)2(1)2(1), respectively. All oligomers adopt the well-known herringbone packing-mode in crystals with packing parameters dependent on the structure of the end-capping units and the number of thiophene rings. The shorter intermolecular distance in NaT3 compared to NaT2 indicates that the intermolecular interaction principally increases with increasing molecular length. X-ray diffraction and atomic force microscopy (AFM) characterization indicate that the NaTn oligomers can form films with better morphology and high molecular order than TNTn oligomers with the same number of thiophene rings. The NaTn oligomers exhibit mobilities that are much higher than those for TNTn oligomers (0.028-0.39 cm(2) V-1 s(-1) versus 0.010-0.055 cm(2) V-1 s(-1), respectively).

Synthesis of bis(amine anhydride)s for novel high T(g)s and organosoluble poly(amine imide)s by palladium-catalyzed amination of 4-chlorophthalide anhydride

Two novel bis(amine anhydride)s, NN-bis(3,4-dicarboxyphenyl)aniline dianhydride (I) and N,N-bis(3,4-dicarboxyphenyl)-p-tert-butylaniline (II), were synthesized from the palladium-catalyzed amination reaction of N-methyl-protected 4-chlorophthalic anhydride with arylamines, followed by alkaline hydrolysis of the intermediate bis(amine-phthalimide)s and subsequent dehydration of the resulting tetraacids. The X-ray structures of anhydride I and II were determined. The obtained dianhydride monomers were reacted with various aromatic diamines to produce a series of novel polyimides. Because of the incorporation of bulky, propeller-shaped triphenylamine units along the polymer backbone, all polyimides exhibited good solubility in many aprotic solvents while maintaining their high thermal properties. These polymers had glass transition temperatures in the range of 298-408 degrees C. Thermogravimetric analysis showed that all polymers were stable, with 10% weight loss recorded above 525 degrees C in nitrogen.The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 95-164 MPa, 8.8-15.7%, and 1.3-2.2 GPa, respectively.