Polymer based optical waveguides on silicon substrate were fabricated and the characteristics of the polyimide used were investigated. The optical waveguides were designed according to the simulation results calculated by beam propagation method. The fabrication began with spinning and curing two polyimide materials as the cladding and the core layers on silicon substrate. The refractive index of polyimide was obtained by prism coupling system. The index contrast was 0.67 % and the waveguide was the ridge type structure obtained by reactive ion etching process. Then a top cladding was spun on the sample and cured to complete the waveguide fabrication. Finally, the propagation loss of the TE mode of the waveguides was measured by using cut-back method. The loss was 2.4 dB/cm.

No description available.

No description available.

The E-beam curable BMI resin systems and phenylethynyl terminated AFR-PEPA-4 oligomer together with an imide model compound N-phenyl-[4-(phenylethynyl) phthalimide] were synthesized and characterized. E-beam exposure cannot propagate the polymerization of BMI system until the temperature goes up to 100oC. However, a small amount of oligomers may be generated from solid-state cure reaction under low E-beam intensity radiation. Higher intensity E-beam at 40 kGy per pass can give above 75% reaction conversion of BMI with thermal cure mechanism involved. NVP is a good reactive diluent for BMI resin. The cure extents of BMI/NVP increase with the increase of the dosage and applied dosage per pass. The reaction rate is much higher at the beginning of the E-beam cure and slows down after 2 dose passes due to diffusion control. Free radical initiator dicumyl peroxide can accelerate the reaction rate at the beginning of E-beam cure reaction but doesn’t affect final cure conversion very much. According to the results from FT-IR, 200 kGy total dosage E- beam exposure at 10 kGy per pass can give 70% reaction conversion of BMI/NVP with the temperature rise no more than 50oC. The product has a Tg of 180oC. The predicted ultimate Tg of cured AFR-PEPA-4 polyimide is found to be 437.2oC by simulation of DSC Tg as a function of cure. The activation energy of thermal cure reaction of AFR-PEPA-4 oligomer is 142.6 ± 10.0 kJ/mol with the kinetic order of 1 when the reaction conversion is less than 80%. The kinetics analysis of the thermal cure of N-phenyl-[4-(phenylethynyl) phthalimide] was determined by FT-IR spectroscopy by following the absorbance of the phenylethynyl triple bond and conjugated bonds. The thermal crosslinking of N-phenyl-[4-(phenylethynyl) phthalimide] through phenylethynyl addition reaction has a reaction order of 0.95 and an activation energy of 173.5 ± 8.2 kJ/mol. The conjugated bond addition reactions have a lower reaction order of 0.94 and lower activation energy (102.7 ± 15.9 kJ/mol). The cure reaction of N-phenyl-[4-(phenylethynyl) phthalimide] can be described as a fast first-order reaction stage followed by a slow second stage that is kinetically controlled by diffusion.

Techn., Hochsch., Diss., 2005--Aachen.

No description available.

No description available.

The aqueous suspension prepregging technique was used to fabricate PEEK and PPS matrix composites with polyimide interphases of tailored properties. The structure-property relationships of Ultem-type polyimide and BisP-BTDA polyimide which were made from various water soluble polyamic acid salts were studied. The molecular weight of the polyimides was shown to be dependant upon the selection of the base used for making the polyamic acid salt. The development of an Ultem-type polyimide with controlled molecular weight and properties similar to commercial Ultem 1000 was accomplished with the Ultem-type TPA+ polyamic acid salt. Both the Ultem-type polyimides and the BisP-BTDA polyimides derived from the NH4+ salt and the TMA+ salt were shown to crosslink at elevated temperatures. Blends of Ultem-type polyimide with PEEK and BisP-BTDA polyimide with PEEK were prepared to study the structure-property relationships of model composite matrices. Since both polyimides are miscible with PEEK, interdiffusion of the polyimides with PEEK is expected, however, the interdiffusion behavior is complicated by the crosslinking mechanism of the polyimides. Ultem-type polyimide interphase, PEEK matrix composites and BisP-BTDA polyimide interphase, PEEK matrix composites were fabricated using the aqueous suspension prepregging technique and evaluated to determine the effects of the interphase properties on the bulk composite performance and durability. Three different Ultem-type polyimides from the NH4+, TMA+ and TPA+ polyamic acid salts were used and two different BisP-BTDA polyimides from the NH4+ and TMA+ polyamic acid salts were used. The transverse flexure strength was used to qualitatively rank the composites by level of interfacial shear strength. The longitudinal tensile strength of the composites was shown to vary with relative interfacial shear strength. The trend of these data qualitatively support the existence of a maximum longitudinal tensile strength at an optimum interfacial shear strength. Notched fatigue testing of the Ultem-type polyimide interphase, PEEK matrix composites showed that the initial split growth rate increased with decreasing relative interfacial shear strength. Ultem-type polyimide interphase, PPS matrix composites were fabricated using the aqueous suspension prepregging technique and evaluated to determine the effects of the interphase properties on the bulk composite performance. Three different Ultem-type polyimides from the NH4+, TMA+ and TPA+ polyamic acid salts were used. The transverse flexure strength was used to qualitatively rank the composites by level of interfacial shear strength. The longitudinal tensile strength of the composites was shown to vary with relative interfacial shear strength. The trend of these data qualitatively support the existence of a maximum longitudinal tensile strength at an optimum interfacial shear strength. / Ph. D.

High temperature composite materials used in aerospace applications are exposed to extremely harsh conditions and must be able to withstand moisture and extremes of temperature. For example, the surface of an aircraft flying at Mach 2.4 has been estimated to reach around 177°C as a result of aerodynamic heating. This thesis has examined the effect of isothermal aging on two high temperature composite materials, a novel CSIRO composite and a commercial composite, both based on bismaleimides. Changes in mechanical properties and resin chemistry at two different temperatures were measured in order to assess the validity of accelerated aging tests. ¶ Delamination is a major cause of failure in materials, therefore, the Mode I interlaminar fracture toughness (GIC) of both materials was measured using the double cantilever beam (DCB) test. After aging at 250°C, the CSIRO CBR 320/328 composites exhibited better retention of GIC than the CIBA GEIGY Matrimid® 5292 composites. After 6 weeks of aging at this temperature, the CBR 320/328 material retained 100% of its initial interlaminar fracture toughness, however the Matrimid® 5292 material retained only 64% of its initial GIC. This trend was reversed at the lower aging temperature, when after 30 weeks of aging at 204°C, GIC was measured at 13% of its original value for the CSIRO composites, whereas it was measured at 64% in the case of the Matrimid® composites. When the fracture surfaces of these specimens were examined using scanning electron microscopy (SEM), the commercial material was observed to show an increasing degree of porosity with aging at 204°C. It was concluded that the good property retention at the temperature, despite this observed porosity, was a result of the excellent fibre/matrix adhesion exhibited by this material. ¶ Chemical degradation of the matrix of the composites was monitored by Fourier Transform Infrared (FTIR) and Raman Spectroscopy. Chemical changes at the core of both of these materials were found to occur concurrently with the observed changes in interlaminar fracture toughness. FTIR analysis of both matrix materials revealed the predominant degradation mechanism to be oxidation, specifically the oxidation of the methylene group bridging two aromatic rings common to the structure of both resins, was substantiated by the ingrowth of a broad peak centred at 1600cm-1. In addition to this, the pyromellitic anhydride unit present only in the CBR 320/328 composites was found to be highly resistant to the effects of aging, whereas the saturated imide, common to the cured structures of both materials, was observed to degrade. ¶ Raman spectroscopy showed an increase in the intensity of a peak at 1646 cm-1 in the Matrimid® 5292 composites aged at 250°C towards the centre of the sample as a result of increased reaction of the allylic carbon-carbon double bond. At 204°C, the degree of reaction increased towards the surface of the material, possibly as a result of a reverse Diels-Alder reaction. The glass transition temperatures of both materials were found to decrease with aging, with the exception of the CSR 320/328 composites aged at 204°C, which initially increased due to continued crosslinking of the resin. ¶ It is concluded that the degradation mechanisms at the two aging temperatures are very different. The reliability of results from accelerated (elevated temperature) aging tests has been drawn into doubt.

This study developed an inexpensive and simple microsensor for detecting volatile organic compounds (VOCs). This developed VOC sensor is composed of a nano-porous polyimide (PI) film doped with carbon black (CB) as the sensing material. The conductivity of the PI/CB film changed after absorbing VOC contents in the air. In general, solid state based VOC sensors which use metal oxide as the sensing materials have to work at a temperature of about 300¡V350¢J. Alternatively, this research developed a VOC sensor capable of sensing VOCs at room temperature, resulting in a sensor system of low energy consumption. A post pore opening procedure by plasma etching is used to enhance the response of the sensor film. SEM images confirm that the micro-pores interconnect with their neighboring pores and also open to the outside air. The film prepared with pore opening procedure exhibit a response of 3 times faster than the film prepared without pore opening. Results indicate that the developed VOC sensor has a good repeatability for detecting VOCs. PI film with 1% (weight percent) of CB has the best sensitivity due to the well dispersion of CB. This research detected 100 ppm ethanol fifth times to show good reproducibility, and detected 10 ppm, 100 ppm, 1000 ppm benzene and ethanol for 24 hours to show long-term stability, and detected 101 ppm¡ã105 ppm widely VOCs concentration. Besides, this sensor has selectivity on specific gas like alcohol and aldehyde, the sensor material has special chemical bond that can connect with specific gas. Moreover, the sensitivity is about 155% at 25 oC and 80% at 60 oC, it is almost 2 times at 25 oC. The moisture can also be detected to avoid the impact on the sensor performance for detecting VOCs, the moisture capacitance changes is 16 times higher than VOCs. The sensor developed in this study provides a simple and straight forward method to fabricate low-cost VOC sensors.