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The effects of elongation upon the structural and electronic properties of the conducting polymer polyaniline have been investigated. In particular, the properties of high molecular weight (ca. 150 000 Daltons) polyaniline have been examined, and the effects of increased molecular weight assessed. A method has been found to elongate the emeraldine base (EB) form up to 700% (l/l(_o)=8). This induces partial molecular alignment in the polymer which, upon doping, exhibits electrical conductivity of up to 700 Scm(_-1) and electrical anisotropy of almost 4.The mechanical properties of high molecular weight emeraldine base have been investigated as a function of elongation. The breaking stress has been observed to increase by almost one order of magnitude for a 500% elongated film compared with its unoriented counterpart. The breaking strain is found to decrease initially with increasing elongation, though no noticeable change is evident for samples elongated to more than 300%. Similarly, Young's modulus increases by a factor of 2 with increased elongation, but above 300% remains approximately constant. The behaviour has been interpreted in terms of the crystalline fraction of the samples. X-ray diffraction experiments have enabled the crystalline fraction of emeraldine base and emeraldine salt (ES) to be assessed. 300% elongated EB samples exhibit increased crystalhnity compared with as-cast samples. However, no further increase in crystallmity is evident for 600% elongated samples. Unoriented ES samples have a crystalline fraction of approximately 0.3. The crystallinity of 300% and 600% elongated ES samples is slightly less than for unoriented ES. The polarised reflectance spectra of EB and ES have been measured in the region 0.5- 5.6 eV. The results show increased optical anisotropy with increasing elongation for EB samples, but no change in anisotropy for ES samples above 300% elongation. A Kramers-Kronig analysis of the reflectance data reveals near metallic behaviour parallel to the dkection of elongation, and a high degree of localisation perpendicular to this direction.

This study examines the effect of varying injectant molecular weight on the penetration of transverse injection jets into a supersonic crossflow. The injectants considered here are methane (W=16.04), air (W=28.97) and carbon dioxide, (W=44.01). These results augment the previous results obtained at Virginia Tech for helium (W=4.00) injection under the same test conditions to provide a very wide range of molecular weights. Second, since shocks are ubiquitous in scramjet combustors, their influence on penetration and mixing was also studied by arranging for an oblique shock to impinge near the injection station. The cases of a shock impinging upstream and downstream of the injector were both examined. One can anticipate an important influence of molecular weight here also because of the importance of density gradients on the generation of vorticity by baroclinic torque. Increasing molecular weight was found to increase penetration in general, as well as increase the lateral spreading of the plume. The majority of the data shows a weak dependency of the jet size on molecular weight, but there are indications that under certain circumstances large changes in the flow structure may occur due to molecular weight effects. The addition of an impinging shock is found to increase mixing and decrease penetration and plume size, especially with the shock impinging downstream of the injector. / Master of Science

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"The effects of molecular weight (Mw) and concentration (c) on the structure of electrospun PVA have been studied. Experiments have been conducted for Mw values ranging from 9000 g/mol to 124,000 g/mol. The concentration was varied from 5 to 35 wt %. Data were acquired for several solvents including water, Dimethyl Sulfoxide, Ethylene Glycol and N-Methyl Pyrrolidone. The transient phenomena occurring during jet breakdown were examined by high speed digital photography. The structure in the electrospun polymer was analyzed by scanning electron microscopy. The fiber diameter distribution for various conditions was characterized by optical image analysis. The effects of additives such as NaCl and Poly Ethylene Glycol on the structure have been studied. The results indicate that a minimum Mw and c corresponding to [h]c ~ 5 or Capillary number, Ca ~ 0.5 is necessary for forming a fibrous structure. As Mw or c increase, the fiber diameter becomes larger and a broader distribution of fibers may be obtained. The average diameter of the fiber, D, follows a Power law relationship: D (nm) = 18.6([h]c)1.11. Round fibers may be obtained at low Mw and c, while flat fibers are observed at high Mw and c. The transition from round to flat fibers appears to begin at [h]c ~ 12. At any [h]c, there is a minimum Capillary and Ohnesorge numbers at which fibers are stabilized and a maximum at which viscous effects become dominant. The addition of NaCl lowers the average fiber diameter in PVA samples with a high molecular weight. Electrospinning can be used to produce nanofibers of PVA with various architectures. "

Doctor of Philosophy (PhD), Engineerig / Free radical emulsion polymerization (FRP) is widely adopted in industry due to its applicability to a wide range of monomers. Despite its many benefits and wide spread use, the fast chain growth and the presence of rapid irreversible termination impose limitations with respect to the degree of control in FRP. Furthermore, producing block copolymers and polymers with complex structures via FRP is not feasible. Closer control of macromolecular chain structure and molar mass, using novel polymerization techniques, is required to synthesize and optimize many new polymer products. Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization is a novel controlled living free radical technique used to impart living characters in free radical polymerization. In combination with emulsion polymerization, the process is industrially promising and attractive for the production of tailored polymeric products. It allows for the production of particles with specially-tailored properties, including size, composition, morphology, and molecular weights. The mechanism of RAFT process and the effect of participating groups were discussed with reviews on the previous work on rate retardation. A mathematical model accounting for the effect of concentrations of propagating, intermediate, dormant and dead chains was developed based on their reaction pathways. The model was combined with a chain-length dependent termination model in order to account for the decreased termination rate. The model was validated against experimental data for solution and bulk polymerizations of styrene. The role of the intermediate radical and the effect of RAFT agent on the chain length dependent termination rate were addressed theoretically. The developed kinetic model was used with validated kinetic parameters to assess the observed retardation in solution polymerization of styrene with high active RAFT agent (cumyl dithiobenzoate). The fragmentation rate coefficient was used as a model parameter, and a value equal to 6×104 s-1 was found to provide a good agreement with the experimental data. The model predictions indicated that the observed retardation could be attributed to the cross termination of the intermediate radical and, to some extent, to the RAFT effect on increasing the average termination rate coefficient. The model predictions showed that to preserve the living nature of RAFT polymerization, a low initiator concentration is recommended. In line with the experimental data, model simulations revealed that the intermediate radical prefers fragmentation in the direction of the reactant. The application of RAFT process has also been extended to emulsion polymerization of styrene. A comprehensive dynamic model for batch and semi-batch emulsion polymerizations with a reversible addition-fragmentation chain transfer process was developed. To account for the integration of the RAFT process, new modifications were added to the kinetics of zero-one emulsion polymerization. The developed model was designed to predict key polymer properties such as: average particle size, conversion, particle size distribution (PSD), and molecular weight distribution (MWD) and its averages. The model was checked for emulsion polymerization processes of styrene with O-ethylxanthyl ethyl propionate as a RAFT based transfer agent. By using the model to investigate the effect of RAFT agent on the polymerization attributes, it was found that the rate of polymerization and the average size of the latex particles decreased with increasing amount of RAFT agent. It was also found that the molecular weight distribution could be controlled, as it is strongly influenced by the presence of the RAFT based transfer agent. The effects of RAFT agent, surfactant (SDS), initiator (KPS) and temperature were further investigated under semi-batch conditions. Monomer conversion, MWD and PSD were found to be strongly affected by monomer feed rate. With semi-batch mode, Mn and <r> increased with increasing monomer flow rate. Initiator concentration had a significant effect on PSD. The results suggest that living polymerization can be approached by operating under semi-batch conditions where a linear growth of polymer molecular weight with conversion was obtained. The lack of online instrumentation was the main reason for developing our calorimetry-based soft-sensor. The rate of polymerization, which is proportional to the heat of reaction, was estimated and integrated to obtain the overall monomer conversion. The calorimetric model developed was found to be capable of estimating polymer molecular weight via simultaneous estimation of monomer and RAFT agent concentrations. The model was validated with batch and semi-batch emulsion polymerization of styrene with and without RAFT agent. The results show good agreement between measured conversion profiles by calorimetry with those measured by the gravimetric technique. Additionally, the number average molecular weight results measured by SEC (GPC) with double detections compare well with those calculated by the calorimetric model. Application of the offline dynamic optimisation to the emulsion polymerization process of styrene was investigated for the PSD, MWD and monomer conversion. The optimal profiles obtained were then validated experimentally and a good agreement was obtained. The gained knowledge has been further applied to produce polymeric particles containing block copolymers. First, methyl acrylate, butyl acrylate and styrene were polymerized separately to produce the first block. Subsequently, the produced homopolymer attached with xanthate was chain-extended with another monomer to produce block copolymer under batch conditions. Due to the formation of new particles during the second stage batch polymerization, homopolymer was formed and the block copolymer produced was not of high purity. The process was further optimized by operating under semi-batch conditions. The choice of block sequence was found to be important in reducing the influence of terminated chains on the distributions of polymer obtained. It has been found that polymerizing styrene first followed by the high active acrylate monomers resulted in purer block copolymer with low polydispersity confirmed by GPC and H-NMR analysis.

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