Applied Mechanics and Materials Vols. 395-396

Abstract: Positive temperature coefficients of resistivity (PTCR) have been realized in lead free Na_0.5Bi_0.5TiO₃ (NBT) based ceramics by (LiCe) addition. The modulations on their volumes have been obtained continuously in the wide temperature range of 50-479 °C. X-ray diffraction and scanning electron microcopy results display that second-phase adulterants exit on NBT grain boundaries, and even create core-shell structures around NBT grains with the increment of additions. Impedance analysis reveals that electrically heterogeneous structures of grain and grain boundaries have contributions to the PTCR effects of NBT-based ceramics, especially for core-shell structure. All results indicate NBT-based system can be used for thermistor applications at high temperature.

Abstract: In this study, electroless plating technology is applied to coat the surface of carbonized bacterial cellulose with Ni. The fiber surfaces and mechanical interfacial properties of these composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and a vector network analyzer. Our experimental results show that the carbonized bacterial cellulose with nickel exhibit remarkably improved electromagnetic interference shielding compared to the pristine carbonized bacterial cellulose. The enhanced shielding ability arises from the electrical conductivities of the nickel and carbon.

Abstract: Emission spectrum of bis [2-(9, 9-diethylfluoren-2-yl)-5-trifluoromethylpyridinto-C³, iridium (2-picolinic acid) (fl-5CF₃-py)₂Ir (pic) in THF was 572 nm. Two weak UV absorption bands can be assigned to spin-allowed singlet metal-to-ligand charge transfer (¹MLCT) and spin-forbidden ³MLCT transitions. The organic light-emitting devices A ITO/PEDOT: PSS/PBD: PVK: (fl-5CF₃- py)₂Ir (pic) (12 %) /LiF/Al, B ITO/PEDOT:PSS/PBD: PVK: (fl-5CF₃-py)₂Ir (pic) (2 %) /TPBi/LiF/Al and C ITO/PEDOT:PSS/PBD: PVK: (fl-5CF₃-py)₂Ir (pic) (12 %) /TPBi/LiF/Al were fabricated using iridium complex as emitter dopant with electroluminescent spectra at 576, 572 and 576 nm, respectively. Devices A, B and C exhibited maximum luminance of 983 cd/m² (at 10 V), 3132 cd/m² (18 V) and 9876 cd/m² (12V), respectively. Device C exhibited more efficient emission. The devices had excellent stability even at the high concentration.

Abstract: nanocomposite used widely with the development of nanotechnology, and the dispersion of different composition is important. ZrO₂ often used as the second phase to improve the toughness of Al2O3 ceramics^[1,. nanoAl2O3 and ZrO2 are added to water to prepare suspension, and PVP was used as dispersant to improve the dispersion of suspension. The suspension of Al₂O₃ and ZrO₂ adjusted from 2 to 11 with the addition of dispersant is 0.5%. The flocculation of suspension was observed after 3h, 6h, 12h and 24h. Result shows that two kinds suspension dispersant better in acid liquid than in alkaline and natural liquid. The pH values that are choose as the best dispersion and flocculation are 5 and 7. Morphology and element distribution of composite powder are tested in the SEM. Results show that the composite powder is finely disseminated.

Abstract: B3LYP /aug-cc-pvdz level of theory, combined with NBO and G3 methods, is applied to study substituent effects on the geometries, bond dissociation energies and high energetic density material properties of 27 kinds of derivatives designed by substituted hydrogen atoms of pentazine, 1,2,4,5-tetrazine and s-triazine, of which the hydrogen atoms are substituted by CN, -NO₂, -NH₂, -N₃, -N₂H, -NHNH₂, -N₄H and-N₄H₃ groups. The relatively small heats of formation are observed for the derivatives substituted by-NH₂, -H, -NO₂ and-NHNH₂. The order of heats of formation for the derivatives containing the same substituent is: pentazine > 1,2,4,5-tetrazine >s-triazine. For the derivatives substituted by-CN, -N₂H and-N₄H₃, heats of formation are 860~1124 kJ/mol,in which heats of formation of 1,2,4,5-tetrazine derivatives are larger. For derivatives substituted by-N₃ and-N₄H, their heats of formation are 974 1735 kJ/mol, which are the highest in all derivatives. The order of heats of formation is: s-triazine derivative > 1,2,4,5-tetrazine derivative > pentazine derivative. The normalized heats of formation of these pentazine derivatives substituted by-CN-N₃ ,- N₂H and N₄H and 1,2,4,5-tetrazine derivatives substituted by-CN-N₃ and N₄H are 93 109 kJ, which is higher than that of triazido-s-triazine and diazido-s-tetrazine derived from Hiskey. Our observations indicate that the higher heats of formation of substituent molecules have, the higher ones the substitutive derivatives. By means of the data of dissociation energy, it can be found that the heats of formation of derivatives substituted by N₃, -N₂H and CN are greater, and they are also more stable. It is possile for them to become energetic materials with high-energy and low sensitivity.

Abstract: PP/mica composites were prepared via melt blending, homemade UV aging box and the constant temperature and humidity aging box were used to study the resistance to aging of the composites, and then the properties were studied by mechanical property test, SEM. Results show that: mica in PP matrix can improve the resistance to UV aging and hygrothermal aging; UVB irradiance within 800h plays a role in improving mechanical properties, the retentions are above 95%; at the beginning of hygrothermal, here are some contributions to tensile strength, the resistance to hygrothermal aging is reducing with the increasing of mica content, when the mica content is 10%, the resistance is best, and the retentions of tensile strength and impact toughness are above 93%.

Abstract: A functional potassium sodium niobate/polyimide (KNN/PI) composite films were prepared in this paper. KNN fillers are well dispersed in the PI matrix without any accumulation through in situ polymerization process. The optical band baps of the hybrid films become smaller with the increase of KNN loading. The optical band baps of the films with 0-20 wt% KNN filler are estimated to be 2.61 eV, 2.57 eV, 2.52 eV, 4.29 eV, 2.35 eV respectively.

Abstract: Transferable microlens-structures were fabricated on the substrate of OLED by using nanoimprint lithography. As a result, the waveguide effect on each organic layer was reduced, which can facilitate the optical coupling of the substrate and is expected to increase luminous efficiency, and finally, the device with high brightness can be fabricated. Firstly, ultraviolet exposure and wet etching technology were combined to fabricate high-precision nanoimprint template with quartz glass; secondly, the cleaning and anti-adhesion treatment were used and finally transferable microlens-structures were fabricated on the substrate of OLED by using hot nanoimprint lithography. The result shows that the lens micro-structures are characterized by good flatness, high nanoimprinting precision. The parameters of micro-structures such as period, diameter and length were optimized using Finite-difference time-domain (FDTD) and finally, the optical crystal micro-structure with the photonic band gap effect was fabricated. The light outcoupling efficiency can be increased effectively due to the photonic band gap effect produced by photonic crystal structures on the substrate of OLED. The measuring result showed that both the emission spectrum and the light intensity were increased.

Abstract: Polymer/TiO2 nanocomposite films have good mechanical, electrical and thermal property, which are applied to electrical engineering and microelectronic technique field extensively. Nano-TiO2 has bigger permittivity and better absorption ultraviolet. The PI/TiO2-PI-PI/TiO2 three layer composite films (30mm) with different content and interlayer thickness were prepared via in-situ dispersion polymerization in this paper. And the films with A (5mm), B (10mm) and C (15mm) interlayer PI thickness are divided into three different series. The results show that inorganic TiO2 nanoparticles are well dispersed in the polymer matrices. And the structures of three layers are obvious. The doped nanoparticles don’t affect the imidization of PI matrix in composite films. The time-to-breakdown of all series films increases with the TiO2 content increasing, in which the B series films possess the best performance. Besides, the B series films with 4% doping content are tested with the longest time-to-breakdown, which is three times more than that of pure PI. After corona aging, there are lots of TiO2-particles with the ability of absorbing UV accumulated on the surface of films, playing the role in shielding electric field, which is one factor resulting in improvement of corona-resistance in the composite films.

Abstract: The present study investigates the preparation of sustained release drug-loaded nanofibers using a modified coaxial electrospinning process where only solvent is exploited as sheath fluid. Drug-loaded ethyl cellulose (EC) nanofibers are successfully generated smoothly and continuously without any clogging through the coaxial process, in which ethanol is used as sheath fluid and EC and ketoprofen (KET) are taken as the filament-forming matrix and active pharmaceutical ingredient, respectively. Field-emission scanning electron microscopic observations demonstrated that the nanofibers diameter can be manipulated through the sheath fluid flow rate. The composite nanofibers are in essential a molecular solid dispersion of EC and KET based on the hydrogen bonding between them, as verified by XRD and ATR-FTIR results. In vitro dissolution tests show that KET in the nanofibers has a fine sustained release profile via a typical Fickian diffusion mechanism. The modified coaxial electrospinning with solvent as sheath fluid can be a useful tool for developing novel sustained release drug delivery nanofibers.