Reflection anisotropy spectroscopy (RAS) is a non-destructive optical technique which can be used to measure the surface properties of sample. We use the technique to detect the optical anisotropy of rubbed polyimide thin film. Atomic force microscopy study of rubbed polyimide showed that rubbing produced microgrooves on the surface of the polyimide thin films, and the surface roughness of the polymer thin films increased slightly with the rubbing strength. Reflection anisotropy signals have been found to be generated on the surface of polyimide thin film on completion of mechanical rubbing, and will increase with an increase in the rubbing strength. We also tried to find out the correlation between RA strength of the polyimide alignment layer and pretilt angle of liquid crystal at the rubbed polyimide films.

To achieve the miniaturization and high performance of the mobile phone, notebook, hearing aid and personal digital assistant (PDA), many researchers focus on the developing a new-type microphone with very small dimension, high quality and low manufacturing cost utilizing MEMS technology. By using the surface and bulk micromachining technologies, this thesis designed and fabricated a capacitive MEMS microphone with a polyimide bcakplate microstructure. The main processing steps adopted in this study include five photolithoghaphies and seven thin-film depositions. A MEMS-based microphone with an only 2¡Ñ2 mm2 sensing area of the floating Si3N4/Poly-Si/Si3N4 membrane and a 2 £gm-height gap distance between the top and bottom electrodes was implemented and characterized. Measured in a special isolated-box and under 1 kHz audio frequency, a -60.3 dB/Pa sensitivity (deducted the 22.6 dB output gain of the pre-amplifier) and a 51 dB signal to noise ratio (SNR) of the implemented MEMS microphone can be obtained as the biasing voltage only about 3 volts. The very low driving voltage, moderate SNR and sensitivity demonstrated in this work keep abreast with the results of many outstanding research laboratories in the world.

The goal of this project was to develop a mixed matrix membrane with enhanced properties for propylene/propane separations. To start with the project, one of the high performance 6FDA based polyimides was identified as the polymer matrix for the rest of the project. The chosen polymer (6FDA-6FpDA) was successfully synthesized in the laboratory. During the synthesis process the key objectives for high molecular weight and low polydispersity index polymer were identified. High molecular weight 6FDA-6FpDA was achieved via laboratory synthesis and was tested successfully. After successful synthesis of the high performance polymer, pure polymer dense films were tested for transport properties. One problem identified with 6FDA-6FpDA polymer films for propylene/propane separations was plasticization. A major objective of this research was to develop a method for plasticization suppression. A carefully controlled annealing procedure with high temperature permeation experiments was used in this research to suppress plasticization in a mixed gas environment. To the best of our knowledge, this is for the first time plasticization suppression was achieved with pure polymeric membrane material for propylene/propane separations with pure and mixed gases. The observed mixed gas experimental selectivity was lower than the pure gas selectivity which was explained by the combination effect of dual mode and bulk flow effect. The last objective of this project was to successfully incorporate molecular sieve materials to form a mixed matrix membrane hybrid material with enhanced transport properties First, an ideal molecular sieve for propylene/propane separation was identified and characterized. AlPO-14 was chosen for this research following its success with propylene/propane pressure swing adsorption. Mixed matrix membranes were successfully produced and tested for enhanced transport properties. Both pure and mixed gas results showed promising results with enhanced propylene permeability and propylene/propane selectivity. The experimental results were modeled with the Cussler and Maxwell models. A modified Cussler model was presented in this work. This is the first time an enhancement in the transport properties with mixed matrix membrane for propylene/propane separations has been observed. This fundamental dense film work holds a bright future for the scale up of propylene/propane separations.

Separation of aromatic/aliphatic hydrocarbon mixtures by pervaporation has been of increasing interest in recent decades. Dozens of polymer materials have been reported for separations of benzene/cyclohexane and toluene/iso-ocatne mixtures. However, fundamental understanding of material structure and transport relations is not adequate to generalize guidelines for materials screening. The goals of this study are to tailor the structure of the polyimide materials, correlate the structure and transport relations, and establish guidelines for future materials. The 3, 5-Diaminobenzoic acid (DABA) containing polyimides were synthesized by both chemical and thermal solution imidization. The synthesized polyimides were formed into dense films by solution casting. The physical properties of the polyimides synthesized with monomers: 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 4, 6-trimethyl-1, 3-phenylendiamine (DAM) and DABA, were characterized by DSC, WAXD, GPC and density. The chemical structures were assessed by FTIR and NMR. The pervaporation and sorption of the synthesized polyimide membranes were tested in toluene/iso-octane mixtures at 100°C. The structure- transport property relations were established for the 6FDA-DAM/DABA membranes. The 6FDA-DAM/DABA polyimides were crosslinked by ethylene glycol. The pervaporation and sorption of the crosslinked membranes were tested in toluene/iso-octane mixtures at 100°C. Thermal imidization was found to give a higher imidization degree than chemical imidization. As a result, the polyimides made by chemical imidization contain a higher percentage of carboxylic acid groups than those made by thermal imidization. Chemical imidization gives higher film density, glass transition temperature and lower flux and higher selectivity for the toluene/iso-octane pervaporation than the thermally imidized membranes because of the higher carboxylic acid concentration. The chemically imidized membranes are slightly brittle after the crosslinking. Only the thermal imidization membranes have good flexibility and its pervaporation selectivity improves significantly after the crosslinking. Solubility selectivity and diffusivity selectivity of the 6FDA-DAM/DABA membranes were correlated with solubility parameters and fractional free volume, respectively. The structure-mass transport relations show that for the 6FDA-DAM/DABA membranes, both solubility selectivity and diffusivity selectivity contribute to the pervaporation selectivity. For the chemically imidized membranes, increased DABA concentration has a positive effect on solubility selectivity and diffusivity selectivity. For the thermally imidized membranes, increased DABA concentration has a significant effect on diffusivity selectivity only. / text

<p>South Africa s coal and platinum mineral resources are crucial resources towards creating an alternative and environmentally sustainable energy system. The beneficiation of these natural resources can help to enhance a sustainable and effective clean energy base infrastructure and further promote their exploration and exportation for economics gains. By diversification of these resources, coal and the platinum group metals (PGMs) especially palladium market can be further harnessed in the foreseeable future hence SA energy security can be guaranteed from the technological point of view. The South Africa power industry is a critical sector, and has served as a major platform in the South African socio-economic development. This sector has also been identified as a route towards an independent energy base, with global relevance through the development of membrane technologies to effectively and economically separate and purify hydrogen from the gas mixtures released during coal gasification. The South Africa power industry is a critical sector, and has served as a major platform in the SA&rsquo / s socio-economic development. This sector has also been identified as a route towards an independent energy base, with global relevance through the development of membrane technologies to effectively and economically separate and purify hydrogen from the gas mixtures released during coal gasification. Coal gasification is considered as a source of hydrogen gas and the effluent gases released during this process include hydrogen sulphide, oxides of carbon and nitrogen, hydrogen and other particulates. In developing an alternative hydrogen gas separating method, composite membrane based on organic-inorganic system is being considered since the other available methods of hydrogen separation are relatively expensive.<br /> &nbsp / </p>

Polymers play an integral part in the semiconductor electronic industry. Due to the expanding diversity of a polymer s structural design and the resulting properties, different polymers serve as different components in the makeup and fabrication of the electronic package. The limiting factor in computer processing speed shifts from the transistors gate delay to the interconnect delay below a circuit line width of 1.8 μm for interlayer dielectrics. Silicon dioxide has been used as the insulating layer between metal lines for many computer chip generations. Low dielectric constant polymers will need to supplant silicon dioxide as interlayer dielectrics in order to develop reliable circuits for future generations. Along with serving as interlayer dielectrics, low dielectric constant polymers are also incorporated in first and second level electronic packaging. Deposition and patterning of these polymers can be significantly reduced by using photodefinable polymers. Most photodefinable polymers are in a precursor form for exposure and development in order to dissolve in industrial developers. Once developed, the polymer precursors are cured to produce the final polymer structure. This temperature is as high as 350 oC for many polymers. Thermal curing sets limitations on the use of the polymer in the electronics industry because of either the unwanted stress produced or the incompatibility of other electronic components that do not survive the thermal cure. In addition to a low dielectric constant and photodefinability, many other properties are needed for successful implementation. Polymers must be soluble in organic solvents in order to spin coat films. Water absorption increases the dielectric constant of the patterned films and can lead to various adhesion problems and cause delamination of the film. Mismatches between the coefficients of thermal expansion in adjacent layers can produce residual film stresses which leads to warping of the substrate or interfacial delamination. The glass transition temperature must be high because the thermal expansion is greatly increased when the glass transition temperature is exceeded. A high Young s modulus is also required to withstand external forces from thermal, electrical, and packaging stresses. The goal of this research was to develop novel, low dielectric, photodefinable polymers that can be processed at low temperatures. All polymers discussed will contain one of two monomers with hexafluoroalcohol (HFA) functional groups. Fluorine provides many properties that are advantageous for low dielectric applications whereas alcohols absorb water and increase the dielectric constant. Characterization of the polymers show the effect the fluorine has on the alcohol s high water absorption. All polymers will be synthesized by condensation polymerization of a diamine with a dianhydride or diacid chloride. All other polymers will contain a novel HFA diamine. A new thermoplastic polymer structure based on the cyclization of an HFA situated ortho to an amide linkage produces a benzoxazine ring in the polymer backbone. Cyclization to form polybenzoxazines occurs at temperatures considerably lower than that needed to form polyimides. The lowest processing temperatures are achieved with protection of the HFA that can be cleaved with a photoacid generator.

Mechanical performance of composite structures is influenced by the accumulation of damage from the manufacturing process and throughout the whole service life. For instance, an aircraft is subjected to a combination of mechanical loading and the thermo-oxidative environment from the take-off to the landing. Therefore, this degree project consists of studying the damage initiation and evolution in carbon fibre reinforced polyimide composites and assesses the thickness effect of the laminated composites. After manufacturing, the level of residual thermal stresses occurring at room temperature lead to the occurrence of microcracks in bundles of the quasi-isotropic composites. Further cooling to cryogenic temperature creates new cracks were appearing. This reinforces the conclusion that cracks are created due to thermal stresses. Comparison between a baseline composite made of carbon fibre T650 8-harness satin weave with thermosetting polyimide resin (ply thickness= 190µm) and thin-ply textile laminate made of Textreme carbon fibre IMS65 (ply thickness=83µm) with the same resin shows that the ply thickness has a significant effect on suppressing or delaying the occurrence and the propagation of microcracks after mechanical loading. It is assumed that there are some edge effects leading to different damage state in 90° and ±45° layers.

To date there exists a great deal of energetic and economic inefficiency in the separation of olefins from paraffins because the principal means of achieving industrial purity requirements is accomplished with very energy intensive cryogenic distillation. Mitigation of the severe energy intensity of the propylene/propane separation has been identified as one of seven chemical separations which can change the landscape of global energy use, and membranes have been targeted as an emerging technology because they offer scalability and lower capital and operating costs. The focus of this work was to evaluate a new direction of material development for the very industrially relevant propylene/propane separation using membranes. The objective was to develop a rational design approach for generating highly selective membranes using a relatively new platform of materials known as polyimides of intrinsic microporosity (PIM-PIs), the prospects of which have never been examined for the propylene/propane separation. Structurally, PIMs comprise relatively inflexible macromolecular architectures integrating contortion sites that help disrupt packing and trap microporous free volume elements (< 20 Å). To date most of the work reported in the literature on this separation is based on conventional low free volume 6FDA-based polyimides which in the best case show moderate C3H6/C3H8 selectivities (<20) with C3H6 permeabilities too low to garner industrial interest. Due to propylene and propane’s relatively large molecular size, we hypothesized that the use of more open structures can provide greater accessibility to the pores necessary to enhance membrane sieving and flux. It has been shown for numerous key gas separations that introduction of microporosity into a polymer structure can defy the notorious permeability/selectivity tradeoff curve and induce simultaneous boosts in both permeability and selectivity. The cornerstone approach to designing state of the art high performance PIM-PI membranes for the light gas separations involving maximizing the intra-segmental rigidity of the polymer chain was applied to the C3H6/C3H8 separation. A study regarding a stepwise maximization of intra-molecular rigidity and its effects on C3H6/C3H8 permeation was evaluated by conducting systematic structural modifications to high performance PIM-PIs. State of the art increases in performance were observed in pure-gas measurements as there were significant increases in C3H6/C3H8 selectivity and C3H6 permeability upon doing so. However, mixed-gas measurements showed that there were 65% losses in selectivity due to competitive sorption and mainly plasticization. Based on the conclusions drawn, a fundamental departure from conventional PIM design principles was used, instead emphasizing enhancing inter-chain interactions by introduction of a flexible diamine and functionalization with hydroxyl groups to attempt to immobilize the polymer chains. In doing so, the polymer chains may be able to pack more efficiently and upon sub-Tg annealing cause a microstructural reorganization to form a coplanarized configuration due to the combination of inter-chain charge transfer complexes (CTC) and hydrogen bonding networks. This approach successfully mitigated plasticization, but more importantly resulted in a tightening of the microstructure, especially in the ultra-microporous range (<7 Å) thereby yielding significant boosts in C3H6/C3H8 selectivity. Based on the PIM platform and novel polymer design approach thereof, the C3H6/C3H8 upper bound was thrust to new limits and led to the generation of the most selective solution processable polymers reported for the C3H6/C3H8 separation. Although the PIM platform has redefined the polymer upper bound, the permeability/selectivity tradeoff still endures, as the C3H6 permeabilities were on the order of 1 to 3.5 Barrer for the most selective polymers. To bridge that gap in permeability, several different approaches were taken. For the first time attempted for C3H6/C3H8 separation, high temperature heating of a PIM-PI to form thermally-rearranged and carbon molecular sieve membranes was employed. The TR membrane showed increased C3H6 permeability and about 50% losses in C3H6/C3H8 selectivity, while the CMS membrane formed at 600 oC showed modest gains in C3H6/C3H8 selectivity with significant improvements in C3H6 permeability. Finally, hybrid nanocomposite membranes incorporating a metal-organic framework structure into a PIM-PI matrix was used. ZIF-8, which has demonstrated high diffusive selectivities for C3H6/C3H8, was dispersed within the polymer, since previous work by the Koros group indicated that its incorporation into polyimide matrices can facilitate major improvements in both C3H6/C3H8 selectivity and C3H6 permeability compared to the respective neat polymer. Focus was directed towards attempting to improve polymer/nanoparticle adhesion by enhancing the interactions between the polymer and filler particles to mitigate the interfacial defects notorious in mixed-matrix membranes (MMM). To do so, ZIF-8 was dispersed into one of the best performing hydroxyl functionalized PIM-PI for the C3H6/C3H8 separation. The highest loaded mixed-matrix membrane in a glassy polymer to date of 65% (w/w) was achieved. The membranes showed pure-gas selectivities ranging from 34 with 10 Barrer at 30% loading to 43 with 38 Barrer at 65% loading. Strong performance and plasticization resistance were sustained in mixed-gas experiments even to feed pressures approaching the vapor pressure of the C3H6/C3H8 mixture, as selectivities well over 20 were achieved with high permeabilities, thereby demonstrating the potential commercial viability. Based on the work reported in this dissertation, we hope to help lay a framework to be able to tailor membrane performance and future membrane design to meet the demands of the different applications of the propylene/propane separation and hence show that there can be a marketplace for membranes in the separation. These include the debottlenecking of cryogenic distillation towers for production of polymer-grade propylene (99.5%) to reduce the associated extensive energy load, production of chemical-grade propylene (92-95% propylene), or for the recovery and recycling of olefins from reactor purges of petrochemical processes.

Thermoplastic polyimides (TPIs) exhibit high glass transition temperatures (Tgs), which make them useful in high performance applications. Amorphous and semicrystalline TPIs show sub-Tg relaxations, which can aid in improving strength characteristics through energy absorption. The a relaxation of both types of TPIs indicates a cooperative nature. The semicrystalline TPI shows thermo-irreversible cold crystallization phenomenon. The polymer liquid crystal (PLC) used in the blends is thermotropic and with longitudinal molecular structure. The small heat capacity change (ACP) associated with the glass transition indicates the PLC to be rigid rod in nature. The PLC shows a small endotherm associated with the melting. The addition of PLC to the semicrystalline TPI does not significantly affect the Tg or the melting point (Tm). The cold crystallization temperature (Tc) increases with the addition of the PLC, indicating channeling phenomenon. The addition of PLC also causes a negative deviation of the ACP, which is another evidence for channeling. The TPI, PLC and their blends show high thermal stability. The semicrystalline TPI absorbs moisture; this effect decreases with the addition of the PLC. The absorbed moisture does not show any effect on the degradation. The addition of PLC beyond 30 wt.% does not result in an improvement of properties. The amorphous TPI + PLC blends also show the negative deviation of ACP from linearity with composition. The addition of PLC causes a decrease in the thermal conductivity in the transverse direction to the PLC orientation. The thermomechanical analysis indicates isotropic expansivity for the amorphous TPI and a small anisotropy for the semicrystalline TPI. The PLC shows large anisotropy in expansivity. Even 5 wt. % concentration of PLC in the blend induces considerable anisotropy in the expansivity. Thus, blends show controllable expansivity through PLC concentration. Amorphous TPI + PLC blends also show excellent film formability. The amorphous TPI blends show good potential for applications requiring high thermal stability, controlled expansivity and good film formability.

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