Papers by Keyword: Polyimide

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Authors: Sang Soon Lee, Mi Hie Yi
Abstract: The residual stresses in a polymeric thin film deposited on Si wafer induced during cooling from a cure temperature down to room temperature are investigated. The laser scanning method and the boundary element method (BEM) are employed to investigate the residual stresses. A 3 μm thick polyimide film is deposited on a relatively thick Si wafer. The normal stress across thickness of the thin film is estimated from wafer curvature measurements to be 20MPa . The boundary element method is employed to investigate the whole stresses in the film. The numerical result for the normal stress across thickness of the film, σ xx , shows good agreement with the experimental result obtained by using the laser scanning method. The singular stress is observed near the interface corner. Such residual stresses are large enough to initiate interface delamination to relieve the residual stresses.
Authors: Dan Dan Cheng, Yun Cheng Shi, Wei Ping Yang, Yan Feng Xie, Ze Yuan Zong
Abstract: Metal films are deposited on polyimide by pulsed cathode arc. Metal film wrinkles are found by SEM. These wrinkles are caused by film stress which is from inherent defect of film materials. The soft substrate will deform with metal films because there is shear force between metal films and soft substrate surface. The film stress with soft substrate together is discussed in detail.
Authors: Jing Fu Song, Gai Zhao, Qing Jun Ding, Jin Hao Qiu
Abstract: Space exploitation and development need high-performance polymer based tribo-materials in order to reduce the weight and improve the reliability of mechanical moving components. However, the wear resistance of polymer composites will decrease after space irradiation. In order to improve the anti-irradiation and wear resistance, the high performance polyimide (PI) composites reinforced with aramid fibers (AF), filled with polytetrafluoroethylene (PTFE) and Al2O3 were designed and prepared using hot press sintering. The effect of the individual atomic oxygen or proton irradiation as well as both on the tribological properties of the PI composites were systematically investigated against Si3N4 ball on a ball-on-disk test rig under simulating space environment system, and coefficient of friction and wear rate were considered as responses. The worn surfaces of the composites were observed by scanning electrical microscopy to reveal wear mechanisms of the materials’ damage. Experimental results indicated that the wear rate of the PTFE/AF/PI greatly increased after atomic oxygen and proton irradiation due to oxidation degradation effect on the polymer matrix. However, filling Al2O3 nano-particles into polyimide matrix can improve the wear resistance because of oxidation layer, gradually formulated during the process of atomic oxygen irradiation, which can protect the polymer composites and avoid further oxidation. This study will expect to provide the helpful guidance for designing high performance polymer based frictional materials in the application of space science.
Authors: Bing Hua Guo, Yu Dong Ren, Lei Chen, Jun Rong Yu, Jing Zhu, Zu Ming Hu
Abstract: A polyimide fiber derived from benzophenone-3,3’,4,4’-tetracarboxylic acid dianhydride (BTDA), toluene diisocyanate (TDI) and 4,4’-methylenebis (phenyl isocyanate) (MDI) has been prepared by wet spinning. The chemical structure of the synthetic polyimide was characterized by Fourier transform infrared (FTIR) spectrometry. Also, field emission scanning electron microscope (FESEM) was used to observe the surface and cross-section morphologies of the resulting fibers. In addition, the obtained fibers possessed good thermal and thermo-oxidative stabilities with the initial degradation temperatures in air and nitrogen 499°C and 527°C, respectively. In order to obtain the optimized processing conditions, orthogonal design was applied. An optimal parameter combination was determined which leaded to maximum of tensile strength . As evidenced by variance analysis, the tensile strength of resultant fibers was influenced by negative draw ratio of spinneret remarkably making it the significant factor.
Authors: Pieter Samyn, Jan Quintelier, Gustaaf Schoukens, Patrick de Baets, Wim De Waele
Abstract: Polyimide surfaces after macroscopic wear at 80 to 260°C are studied by atomic force microscopy to give additional insight in the tribophysical and -chemical processes during sliding. Three sliding regimes are distinguished with hydrolysis resulting in rough surfaces, imidisation resulting in orientation of polymer molecules and melting resulting in short-range arrangements.
Authors: Zhuo Chen, Jun Guo, Hao Li Qin, Hui Xie, Ke Jia Liu, Wei Zhao, Ji Ping Liu
Abstract: Polyimide/nano-SiO2 (PI/SiO2) composites with different contents of SiO2 were prepared by in situ polymerization. The transmittance, solubility, thermal property, flame retardant properties and mechanics properties of PI/nano-SiO2 composites were investigated. The results showed that with the increased addition of SiO2 content, the transmittance of PI/SiO2 compositions reduced; tensile strength changed with the amount of nanometer powder, when the addition content was 10 wt%, it achieve the maximum value. Thermal resistance of the composite was improved obviously while with the amount of nanometer powder increased, volume resistivity coefficient of volume resistance would have decreased.
Authors: Xiang Li Meng, Ling Jiang, Yu Dong Huang
Abstract: - 5-amino-2(p-aminophenyl) benzoxazole (AAPB) and its derived polyimide prepared with pyromellitic dianhydride (PMDA) were synthesized successfully. Their structures were characterized by FT-IR, 1H NMR, Element analysis, 13C NMR, Solid-state 13CNMR, DSC, TG and XRD. The polyimide was synthesized via a conventional two-stage method. The intermediate poly (amic acid) had inherent viscosity of 1.06dL/g and could be thermally converted into light yellow polyimide film. The polyimide showed excellent solvent resistance and good thermal stability. The glass transition temperature (Tg) was found to be 314°C, the decomposition started at a temperature above 500°C in air and above 550°C in argon atmosphere. The thermal degradation of the polyimide was studied by thermogravimetric analysis (TGA) in order to determine the actual reaction mechanisms of the decomposition process. The apparent activation energy (Ea) was obtained following Flynn-Wall-Ozawa method. The activation energies of different mechanism models and pre-exponential factor (A) were determined by Coats-Redfern method. Compared with the value obtained from the Ozawa method, the actual reaction mechanism obeyed three-dimensional diffusion model, Jander equation (D3) with integral form g(α)=[1-(1-α)1/3]2.
Authors: Samir Zelmat, Marie Laure Locatelli, Thierry Lebey
Abstract: Silicon carbide (SiC) is a wide bandgap semiconductor suitable for high-voltage, highpower and high-temperature applications [1]. However, and among other issues, the production of advanced SiC power devices still remains limited due to some shortcomings of the dielectric properties of the passivation layer [2]. Due to their supposed high operating temperature and dielectric strength [3], spin coated polyimide materials appear as a possible candidates for SiC device passivation and insulation purposes. As a matter of fact, they are already used in current commercial SiC devices allowing a maximum junction temperature of 175 °C. The aim of this paper is to study the ability of polyimide (PI) coatings to be used for a Tjmax up to 300 °C. Therefore, the main electrical properties (dielectric permittivity, leakage current and breakdown field) at different temperatures of a high temperature commercially available polyimide material (from HD Microsystems) in both Metal-Insulator-Semiconductor (MIS) and Metal-Insulator-Metal (MIM) structures are presented and discussed.
Authors: Hwan Pil Park, Yoon Chung, Chong Seung Yoon, Sung Su Jo, Young Ho Kim
Abstract: We developed a simple method of producing metal oxide nanoparticles by reacting a polyamic acid (PAA) with Cu or Sn metal films. Respective particle size, distribution, and morphology were characterized by transmission electron microscopy (TEM). The morphology of metal oxides dispersed in the polyimide is different in Cu and Sn metal films. The Cu2O particles were formed by the dissolution reaction between the polyamic acid and the Cu films. During curing, PAA dehydrates and converts to polyimide, accompanied by precipitation of Cu2O particles. The synthesized Cu2O particles were randomly dispersed within the polyimide. And their particle size was relatively uniform, having a narrow distribution. Mostly nanosize Cu2O particles were formed in the specimen made from 10 nm thick Cu film and the mixture of nanosize particles and Cu layers were observed in the 30 nm thick Cu film. On the other hands, the Sn film undergoes surface reaction with the polyamic acid. Therefore, the synthesized SnO2 particles existed only at the surface of the substrate. SnO2 particle size distribution was not uniform in the polyimide. Although particles were not distributed uniformly in the polyimide, they were confined in a monolayer. The different particle distributions were attributed to the reactivity difference of PAA with Cu and Sn films.
Authors: Ching Wen Hsieh, Yi Hsin Chen, Ru Jong Jeng, Sheng Hong A. Dai
Abstract: A convergent synthetic approach was applied to 4-(2, 4-diaminophenoxy) phthalic acid ethyl esters (DAPPAcE) by reacting it with mono-anhydride in each successive step and this approach was found to be highly efficient in getting three generations of PI dendrimers than all known dendritc strategies carried out so far in PI preparation.The structures of prepared PI dendritic anhydride intermediates of three generations, [ and PI dendrimers, [, were all positively characterized by 1H-NMRFT-IR and mass spectrometry. GPC analyses showed molecular weight distributions are 1.02 (for [G-[B]), 1.04 (for [G-[) and 1.07 (for [G-[) indicating that they all possess narrow molecular distributions. All PI dendrimers have excellent thermal properties. The 5wt % loss temperature of intermediates [G-[ (X=1, 2, and 3) are between 383°C and 390°C, while their respective [G-[ PI dendrimers (X=1, 2, and 3) are between 412°C and 421°C. [G-[ (X=1, 2, and 3).They all exhibit good solubility behaviors in most organic solvents, and their solubility do not show any appreciable difference between generations.
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