Papers by Keyword: Polyimide

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Authors: Pieter Samyn, Alessandro Ledda, Jan Quintelier, Isabel Van Driessche, Gustaaf Schoukens, Patrick de Baets, Wim De Waele
Abstract: Polymer wear debris particles undergo a thermal and mechanical (shear) cycle since their generation and therefore contain information on the friction and wear processes, while it is often difficult to draw quantitative data from them relating to transitions in tribological behaviour. Results from thermal DTA/TGA analysis and morphological pattern spectra of debris are presented and related to a transition at 180°C sliding temperatures own to hydrolysis and imidisation.
Authors: Si Wei Liu, Qiao Ying Cao, Yi Zhang, Zhen Guo Chi, Jia Rui Xu
Abstract: A novel type of liquid crystalline polyimide with good electroactive properties has been successfully synthesized through polycondensation in the component solvent of benzene sulfonyl chloride, dimethyl formamide and pyridine by N,N’-hexane-1,6-diylbis(trimellitimides), p-hydroxybenzoic acid, 4,4'-dihydroxybenzophenone and double amino-capped aniline trimer (N1,N1'-(1,4-phenylene)bis(benzene-1,4-diamine)). The structure of the obtained polymer was characterized and verified. The polymer can be dissolved in the component solvent of phenol and chloroform or DMF, NMP alone, et al. The molecular weight (Mn=1.7×104, Mw=8.2×104,PDI=4.8) was determined by gel permeantion chromatography using DMF as eluent. By combining the excellent properties of both polyimide and oligoaniline, such material could be used in more broad fields. Furthermore, due to the orientation properties of liquid crystalline property, the conductivity of this polymer is anisotropic, with 10-6 S/cm along the shear direction vs. 10-7 S/cm perpendicular to the shear direction.
Authors: Li Xiao, Zhan Zhao, Li Dong Du, Zhen Fang, Shao Hua Wu
Abstract: In this paper, a new structure of polyimide-based humidity sensor is developed, which can work better at low temperature environment. In this humidity sensor, the capacitive part is sputtered on a suspended membrane, the lower electrode is also a controllable heater, used to control the temperature on the surface of the sensor through the external circuits. The results of experiment suggest that the sensor has a wide range of sensing ambient relative humidity from 10%RH to 90%RH with a controllable constant temperature and at a lower temperature it shows a good linearity.
Authors: Yuhei Okubo, Hiro Ota, Kazuki Syoji, Satomitsu Imai
Abstract: A MEMS actuator using a magnetic fluid enclosed with polyimide (PI) diaphragms is proposed. The actuator produces a large displacement and force thanks to its structure in which a magnetic fluid is confined between two thin-film PI diaphragms (diameter: 5 mm) fabricated on two silicon substrates. The two substrates with diaphragms are glued together by sandwiching a polyester sheet to form a diaphragm unit. The thickness of the diaphragms is 8.5 µm so that they can deflect greatly. The magnetic fluid inserted between the two diaphragms is composed of magnetite and isoparaffin. The diaphragm unit (containing the magnetic fluid) is deflected by applying an external magnetic field to it with a magnet coil. Response times and displacements of the diaphragms were measured when a magnetic field was applied. Under an applied voltage of 10 V, the diaphragm unit could produce displacements of 4 µm at the diaphragm center. Response time to reach 90% of the maximum diaphragm displacement was about 2 s. Under an applied voltage of 80 V, force generated by the diaphragm unit was 0.065N. It is concluded from these experimental results that the proposed actuator is applicable to MEMS devices such as micro pumps and give another example here.
Authors: Guang Feng Shi, Peng Zhang
Abstract: Membrane reflector is light enough and deployable for launching into the space for large aperture telescope. Processes of design, computation, analysis, assembly, control, and measurement of a prototype of electrostatic polyimide reflector are introduced in this paper. And, a numerical control algorithm and a measurement algorithm based on the phase-shift and incoherent imaging method are developed for this prototype. The measurement results are analyzed and the trial experience is concluded, which is very helpful for further research work in membrane reflector in the future in China.
Authors: Li Zhe Liang, Quan Gan, Paul Nancarrow
Abstract: In recent years, the utilisation of ionic liquids supported on porous polymer membranes has been demonstrated to enhance gas separation performance by improving both permeability and selectivity for several industrially-relevant gas mixtures. However, the use of such supported ionic liquid membranes (SILMs) is normally not feasible at elevated process temperatures due to the resulting decrease in ionic liquid viscosity, which can lead to increased loss of ionic liquid from the membrane support during operation. In addition, many of the polymer membranes typically used in SILMs exhibit relatively poor mechanical and thermal stabilities at high temperatures. To overcome these problems associated with SILMs, thermally-stable composite ionic liquid and polymer membranes (CILPMs) have been fabricated in this study, thus exploiting the beneficial properties of ionic liquids for gas separation at elevated temperatures. Poly (pyromellitimide-co-4,4-oxydianiline) (PMDA-ODA PI) in combination with the ionic liquid, [C4mi [NTf2] were used to fabricate the CILPMs. A measurement rig was designed and built to determine permeabilities and selectivities of the CILPMs for H2, N2, CO, CO2 and CH4 over a range of pressures and temperatures. The fabricated CILPMs were shown to maintain excellent mechanical and thermal stability over a wide range of processing conditions. Temperature was shown to greatly affect both permeability and selectivity of the membranes, whilst pressure had less influence. The incorporation of [C4mi [NTf2] into the membranes was found to significantly increase CO2 permeation and, therefore, it is anticipated that these CILPMs hold significant potential for CO2 separation applications.
Authors: Hua Jun Fang, Xing Ming Liu, Li Tian Liu
Abstract: a new structure of the uncooled amorphous silicon (α-Si) infrared detector has been fabricated and characterized. The structure with thermal isolation and infrared absorption based on polyimide (PI) and bottom metal reflective layer is put forward. The fabrication process of the IR detectors is described. The temperature coefficient of resistance (TCR) of α-Si resistance has been investigated. The measurements show that the TCR is up to -2.8%. The detectivity of 1.7×108 cmHz1/2W-1 is achieved with chopping frequency of 30Hz at a bias voltage of 5V. Measurement results indicate that the polyimide layer exhibits excellent thermal isolating characteristics and the unique sandwich IR absorption structure is beneficial to the enhancement of detectivity. Compared with other techniques, the IR detectors using PI as thermal isolation layer are not only with simpler process, lower cost and higher yield, but also suitable for the application of large-scale uncooled infrared focal plane arrays (IRFPA).
Authors: Heng Feng Li, Guo Wen He, Jun Li, Jun Chen, Jiang Cong Chen
Abstract: A series of polyimide composites with various mass fractions of multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization. MWNTs were treated with an acid mixture and sulfoxide chloride in turn to increase the chemical compatibility of carbon nanotubes with the polyimide matrix. The modified MWNTs are dispersed homogeneously in the matrix while the structure of the PI and MWNTs structures are stable in the preparation process. The composite films hold preferable thermal stability as same as the pure PI. The dielectric constants of the composites decreased with the increasing frequency and increase sharply with the adding of MWNTs.
Authors: Jian Fei Xie
Abstract: Electrospun membrane filters used to remove particles from hot gases were highly desired to meet the requirement of application in high temperature. Polyimide is a kind of high performance polymer, especially for excellent thermal stability and chemical resistance. In this paper, the polyimide precursor poly (amic acid) (PAA) was synthesized from 3,3’,4,4’-oxydiphthalic anhydride (ODPA) and 4,4’-methylenedianiline (MDA), the polyimide (PI) ultrathin fiber membrane was fabricated by electrospinning and followed by thermal imidization. Scanning electron microscope (SEM), infrared spectrometry (IR), and thermogravimetric analysis (TGA) were used for the characterizations of the polyimide ultrathin fiber Membrane, the tests show that the diameter of ultrathin fiber is uniform with an average size of around 400nm and the membrane is thermally stable at a high temperature of 500°C.
Authors: Yuan Yuan, Bing Xie, Yu Wang
Abstract: A series of polyimide thin films were prepared successfully based on bis[3,5-dimethyl-4- (4-aminophenoxy)phenyl]methane (BDAPM), 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene (BAOFL) and different dianhydrides. And an interesting result of dielectric property for polyimide thin films was found that the polyimide thin film prepared with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) exhibited high dielectric constants of 5.7 at 1MHz. Conversely, the other polyimides possessing fluorene groups showed low dielectric constants. The structures and the mechanical properties of polyimide films also proved the reason for results of dielectric properties.
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