Soluble polyimide as liquid crystal perpendicular alignment layer

Journal of Materials Science - Three polyimides (PIs) were prepared from a diamine containing biphenyl ester group as a side chain and a corresponding dianhydride chosen from...     

Microstructure,shear strength,and nanoindentation property of electroplated Sn–Bi micro-bumps

In order to investigate the microstructure and mechanical properties of small sized Sn–Bi bump, the eutectic Sn–Bi bumps with a diameter of 25 μm and a height of less than 20 μm after reflow were fabricated by electroplating and reflow. The reflow temperature of the Sn–Bi bumps was 170 °C, and the reflow times were varied from 5 to 20 min. The experimental results showed that a eutectic Sn–Bi composition was obtained by plating at a current density of 30 mA/cm² for 15 min. The average height and diameter of the bumps reflowed for 5 min were 16.1 ± 0.7 μm and 25.2 ± 0.7 μm, respectively. The microstructure of the reflowed bumps consisted of Sn- and Bi-rich phases. The thickness of the IMC of Cu₆Sn₅ increased from 1.17 to 2.25 μm with increasing reflow time from 5 to 20 min. The shear strength of the reflowed Sn–Bi bump increased with increasing reflow time, and reached approximately 11 gf at 15 and 20 min. The elastic modulus and hardness of eutectic Sn–Bi bump by nanoindentation were 53.5 and 0.43 GPa. Those of Cu₆Sn₅ were found to be 121.1 and 6.67 GPa.     

Effect of aluminum nitride-scandia content on the microstructural and mechanical properties of sintered silicon carbide ceramics

Two different SiC ceramics, one with 10 vol.% AlN-Sc₂O₃ in a 2:3 molar ratio, and the other with 20 vol.% of the same additives with the same ratio, were fabricated by hot-pressing at 1900 °C for 1 h and subsequent annealing at 2000 °C for 6 h in nitrogen. The grain boundary structures of both materials were observed by using high-resolution transmission electron microscopy. The results showed that both materials had clean boundaries without any amorphous films. Although both samples exhibited the same boundary structure, the sample with the higher AlN-Sc₂O₃ content contained more junction phases. The SiC ceramic with 10 vol.% AlN-Sc₂O₃ maintained its room-temperature strength up to 1400°C, whereas the SiC ceramic with 20 vol.% AlN-Sc₂O₃ showed a gradual decrease in strength at above 900 °C. The present results suggest that the high-temperature strength is dependent on the amount of junction phase, as well as the characteristics of the intergranular phase.     

Low-loss and thermally stable TE-mode selective polymer waveguide using photosensitive fluorinated polyimide

A low-loss, thermally stable TE-mode selective optical waveguide was fabricated using a photosensitive fluorinated polyimide. The polymer undergoes photocrosslinking under UV exposure, thus changing its refractive index. The photocrosslinking-induced refractive index change was utilized to form channel waveguides. The propagation losses of the photosensitive fluorinated polyimide waveguides were less than 0.3 and 0.5 dB/cm for TE polarization at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The measured polarization extinction ratio was higher than 29 and 28 dB at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The refractive index of fluorinated polyimide film remains almost constant after being stored at 150/spl deg/C for 600 min.     

Mechanical properties of SiC ceramics sintered with RE<Subscript>2</Subscript>O<Subscript>3</Subscript> (RE: Sc,Lu, Y) and AlN additives

Highly densified Silicon Carbide (SiC) ceramics with 10 vol.% sintering additives, RE₂O₃ (RE: Sc, Lu, Y) and AlN, were prepared via hot pressing in N₂ atmosphere. The influence of sintering additive composition on the mechanical properties of the sintered specimens is discussed. The Sc₂O₃-AlN system consisted of equi-axed grain structure, while the Lu₂O₃-AlN and Y₂O₃-AlN systems rendered largely grown platelet grains. While fracture toughness was enhanced with regards to the contribution of crack deflection and crack bridging mechanisms for intergranular fracture, strength remained almost the same for all specimens.     

Effect of hot-forging on mechanical properties of silicon carbide sintered with Al2O3-Y2O3-MgO

The mechanical properties of hot-pressed and hot-forged SiC were investigated. The hot-forging of the hotpressed SiC was carried out at 1700 °C for 66 h under an applied pressure of 25 MPa in an argon atmosphere. The microstructures on the surfaces parallel and perpendicular to the pressing direction of the hot-pressed and hot-forged SiC were similar, and no texture development was observed because of the lack of massive β→α transformation of SiC. An increase in hardness of about 13 % and fracture toughness of about 33 % was achieved in the hot-forged specimens compared to the hot-pressed specimens.     

Synthesis and characterization of sulphonated polymer derived from 6FDA-ODA polyimide

Summary 6FDA-ODA polyimide was sulfonated with concentrated sulfuric acid at room temperature in order to convert the polymer into proton-conducting polymer. The sulfonation process was supervised with UV-vis. The results indicated that the reaction carried out quickly and was agreement with the analysis of resulted polymer. The sulfonation degree can be controlled by reaction time. The structure of the resulted polyelectrolytes were analyzed and confirmed by NMR, FT-IR. There are two weight-loss steps at 300 and 500 °C in TG curves, which correspond to the presence of two degradation processes for –SO₃H and polymer backbone. It indicated that the sulfonated polyimide had good thermo stability. The solubility of sulfonated polymer are also discussed.     

Synthesis and characterization of photosensitive poly(imide sulfonates) for fuel cell application

The novel sulfonated polyimide membranes were successfully synthesized by thermal imidization with monomers of 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4’-diamino-diphenyl ether-2,2’-disulfonic acid (SODA) and 3,3’-diaminochalcone (3DAC). Photosensitive chalcone moiety was introduced to the main chain of copolymers, and the photocrosslinking of resulting copolymer in aqueous electrolyte was attempted. A series of sulfonated copolyimide precursors containing chalcone functional groups in the main chain were prepared with different sulfonation degrees by controlling the molar ratio of SODA, 6FDA and 3DAC. The polymer membranes were prepared from these sulfonated aromatic precursors by solution casting and subsequent thermal imidization. The crosslinking with UV irradiation was attempted in the presence or absence of distilled water. The characterizations of the resulting membrane such as the ion-exchange capacity, water absorption and ionic conductivity were performed with respect to the copolymer compositions and the photocrosslinking conditions.     

Synthesis and properties of novel photosensitive poly(arylene ether sulfone) containing chalcone moiety in the main chain

A new series of photosensitive poly(arylene ether sulfone)s containing chalcone moiety in the main chain were synthesized from 4,4′-dihydroxychalcone (4DHC), 4,4′-difluorodiphenylsulfone (DFDPS) and bisphenol A (BPA). This series of polymers were characterized by ¹H NMR, FT-IR, UV spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The polymers were stable up to 400 °C, which indicates that the polymers possess good thermal properties. The polymers were found to be soluble in polar solvents and chlorinated solvents. However, the polymers were insoluble in hydrocarbons and in hydroxyl group-containing solvents. After the irradiation of UV light, the thin polymer film was crosslinked to give an insoluble film in the absence of a photoinitiator or sensitizers. The rate of photocrosslinking was also examined and discussed.     

Effect of annealing on mechanical properties of silicon carbide sintered with aluminum nitride and scandium oxide

Beta-SiC powder samples containing 1 wt.% α-SiC as a seed and 10 vol.% AlN-Sc₂O₃ as a sintering additive were hot-pressed at 1900 °C for 1 h and subsequently annealed at 2000 °C for 1 h, 3 h and 6 h. When the annealing time was increased, the microstructure changed from equiaxed to elongated grains, which resulted in a self-reinforced microstructure consisting of elongated grains (hexagonal platelet grains in 3-dimensions). The development of a self-reinforced microstructure resulted in significant improvement in toughness. However, the improved toughness was offset by a reduction in strength. The typical fracture toughness and strength of the ceramics annealed for 6 h were 7.3 MPa·m^1/2 and ∼500 MPa, respectively.