<p>Single-walled carbon nanotubes (SWNTs) are of special interest in current research due to their extraordinary mechanical, electronic and optical properties. Their unique structure, remarkable thermal and electrical conductivity, and high mechanical strength make SWNTs viable candidates for a wide range of device applications. However, pristine CNTs are not dispersible in most solvents, the main difficulties in CNT applications are related to their purification and solution-phase processing. In recent years, the supramolecular functionalization of SWNTs with conjugated polymers has received significant attention. Research within this field has been driven by the desire to find polymer structures that can selectively disperse certain nanotubes species with high efficiency.</p> <p>After a brief overview of the studies that are related to the investigation of the supramolecular interaction between various conjugated polymers and SWNTs (chapter 1), the synthesis of fluorene and thiophene-based conjugated polymers and their supramolecular complex formation properties with SWNTs are described (chapter 2, 3, 4, 5 and 6). In order to understand the effect that conjugated polymer structure has on formation of supramolecular complexes with SWNTs, various factors were investigated by: (1) altering the polymer backbone composition; (2) varying the polymer molecular weight; (3) introducing different solubilizing groups while the polymer backbone remained the same; (4) changing the polymer conformation. All of the resulting polymer-nanotube assemblies exhibit excellent solution stability in THF in the absence of excess unbound free polymer. The spectroscopic characterization of the polymer-SWNT complex materials indicated that the interaction between the conjugated polymers and SWNTs is strongly influenced by polymer structure.</p> <p>The interaction between a water soluble polythiophene derivative, poly[3-(3-N,N-diethylaminopropoxy)-thiophene] (PDAOT), and SWNTs is discussed in chapter 7. It is also demonstrated that the PDAOT-SWNT complexes form stable aqueous solutions that can be used for the fabrication of highly sensitive amperometric glucose biosensors.</p> / Doctor of Philosophy (PhD)

The commercialization of proton exchange membrane (PEM) fuel cells depends largely upon the development of PEMs whose properties are enhanced over current perfluorinated sulfonic acid PEMs. Understanding how a PEM's molecular weight and morphology affect its relevant performance properties is essential to this effort. Changes in molecular weight were found to have little effect on the phase separated morphologies, water uptake, and proton conductivities of random copolymers. Changes in block length, however, have a pronounced effect on multiblock copolymers, affecting surface and bulk morphologies, water uptake, proton conductivity, and hydrolytic stability, suggesting that multiblock copolymer PEM properties may be optimized by changes in morphology. A major goal of current proton exchange membrane fuel cell research involves developing high temperature membranes that can operate at ~120 °C and low humidites. Multiblock copolymers synthesized from 100% disulfonated poly(arylene ether sulfone) (BPSH100) and naphthalene polyimide (PI) oligomers may be an alternative. At block lengths of ~15 kg/mol they displayed no morphological changes up to 120 °C or even higher. Water desorption was observed to decrease with increasing block length. The copolymers exhibited little to no water loss during a 200 °C isotherm in contrast to random BPSH copolymers and Nafion. A BPSH100-PI multiblock copolymer with large block length appears to have morphological stability and retain water at temperatures exceeding 120 °C, suggesting its candidacy as a high temperature PEM. A growing number of alternative PEM research efforts involve multiblock copolymer chemistries, but little emphasis is placed on the methods used to couple the oligomers. Fluorinated linkage groups can help increase block efficiency during coupling, but their effect on a PEM is not well-known. The choice of linkage type, hexafluorobenzene (HFB) vs. decafluorobiphenyl (DFBP), appears to have small but observable influences on multiblock copolymers with disulfonated and unsulfonated poly(arylene ether sulfone) oligomers. DFBP linkages promote greater phase separation than HFB linkages, resulting in increased stiffness, decreased ductility, and increased proton conductivity at low humidities. DFBP linkages also promote more surface enrichment of fluorine, causing changes in surface morphology and slightly increased water desorption, but determining the impact on actual fuel cell performance requires further research. / Ph. D.

Polymers containing poly(1,3-cyclohexadiene) were synthesized using a novel pre-formed initiator comprised of an alkyllithium and a tertiary diamine. The use of a pre-formed intiator at moderate temperatures (25° C) enabled the synthesis of high molecular weight poly(1,3-cyclohexadiene) homopolymers (<Mn> = 50000) with narrow molecular weight distributions (<Mw>/<Mn> = 1.20). In contrast, the use of a conventional anionic initiation approach resulted in polymerizations that lacked significant degrees of livingness, which limited the polymer molecular weights to approximately 10000. Use of the preformed initiator resulted in a reduction in the degree of both chain termination and chain transfer. In addition, the livingness of the polymerization was shown to be a function of the monomer concentration and the polymerization temperature. The regiochemistry of the polymers were shown to be dependent on the tertiary amine used in the polymerization, which provided a route for the synthesis of polymers with a microstructure rich in either high 1,2-addition (70%) or high 1,4-addition (90%). A range of analytical methods were employed to determine the stereo and regiochemistry of poly(1,3-cyclohexadiene). These methods included 1H NMR, 13C NMR, and endgroup functionalization of the propagating center with chlorotrimethylsilane. The impact of regiochemistry on the thermal properties was examined using differential scanning calorimetry. In addition, the thermooxidative properties of these poly(1,3-cyclohexadiene) polymers were characterized in a series of oxidative studies and the onset of oxidative degradation occurred at 110° C. Perfectly alternating copolymers of poly(1,3-cyclohexadiene-alt-styrene) were synthesized, and the reactivity ratios for these copolymers (r1,3CHD = 0.022, rstyrene = 0.024) were determined using a conventional Mayo-Lewis approach. The effect of aromatization and hydrogenation on the thermal properties of these copolymers was determined using thermal gravimetric analysis and differential scanning calorimetry. The synthesis of poly(1,3-cyclohexadiene) DVB coupled star-shaped polymers was performed using a convergent arm-first approach in combination with a divinylbenzene coupling agent (PDI = 1.25). Well-defined poly(1,3-cyclohexadiene-block-isoprene)-star shaped polymers were synthesized and utilized for the development of novel high temperature thermoplastic elastomers, with excellent elastomeric properties (percent elongation = 745 %, tensile strength = 7.2 MPa). Atomic force microscopy in combination with differential scanning calorimetry verified the presence of microphase separation between the blocks. / Ph. D.

The predicted protein product of open reading frame slr0328 from Synechocystis sp. PCC 6803, SynPTP, possesses significant amino acid sequence similarity with known low molecular weight protein tyrosine phosphatases (PTPs). To determine the gross functional properties of this hypothetical protein, open reading frame slr0328 was cloned, and its predicted protein product was expressed in E. coli. The recombinant protein, SynPTP, was purified by metal ion column chromatography. The catalytic activity of SynPTP was examined toward several exogenous protein substrates that had been phosphorylated on either tyrosine residues or serine residues. SynPTP exhibited phosphatase activity toward tyrosine phosphorylated protein substrates (Vmax toward phosphotyrosyl 32P-casein was 1.5 nmol/min/mg). However, no phosphatase activity was detected toward serine phosphorylated protein substrates. SynPTP displayed phosphohydrolase activity toward several organophosphoesters including para-nitrophenyl phosphate (p-NPP), beta-napthyl phosphate and phosphotyrosine but not toward alpha-napthyl phosphate, phosphoserine, or phosphothreonine. Kinetic analysis indicated that the Km (0.6 mM) and Vmax (3.2 mmole/min/mg) values for SynPTP toward pNPP are similar to those of other known bacterial low molecular weight PTPs. The protein phosphatase activity of SynPTP was inhibited by sodium orthovanadate, a known inhibitor for tyrosine phosphatases, but not by okadaic acid, an inhibitor for many serine/threonine phosphatases. Mutagenic alteration of the predicted catalytic cysteine, Cys7, to serine abolished enzyme activity. Several phosphotyrosine containing proteins were detected from the whole cell extracts of Synechocystis sp. PCC 6803 through immunoreactions using anti-phosphotyrosine antibody. SynPTP was observed to dephosphorylate three of these proteins in vitro. Two of these proteins were identified by peptide-mass fingerprinting analysis, as PsaD (photosystem I subunit II) and CpcD (phycocyanin rod linker protein). In addition, several phosphotyrosine proteins were detected from the soluble and membrane fractions of Synechocystis sp. PCC 6803 cell extracts by in vitro substrate trapping as potential endogenous substrates of SynPTP. Two of these proteins were identified as the alpha and beta subunits of phycocyanin. We therefore speculate that SynPTP might be involved in the regulation of photosynthesis in Synechocystis sp. PCC 6803. / Ph. D.

Void-free phenolic networks have been prepared by the reaction of phenolic novolac resins with various diepoxides. The stoichiometric ratio can be adjusted to achieve networks with good mechanical properties while maintaining excellent flame retardance. A series of linear, controlled molecular weight, 2,6-dimethylphenol endcapped cresol novolac resins have been synthesized and characterized. The molecular weight control was achieved by adjusting the stoichiometric ratio of cresol to 2,6-dimethylphenol and using an excess of formaldehyde. A dynamic equilibrium reaction was proposed to occur which allowed the targeted molecular weight to be obtained. A 2000 g/mol ortho-cresol novolac resin was crosslinked by a diepoxide oligomer and by an epoxidized phenolic oligomer in defined weight ratios and the structure-property relationships were investigated. The networks comprised of 60 or 70 weight percent cresol novolac exhibited improved fracture toughness, high glass transition temperatures, low water uptake, and good flame retardance. The molecular weights between crosslinks were also determined for these networks. The stress relaxation moduli were measured as a function of temperature near the glass transition temperatures. Crosslink densities as well as the ability to hydrogen bond affect the glassy moduli of these networks. Rheological measurements indicated that cresol novolac/epoxy mixtures have an increased processing window compared to phenolic novolac/epoxy mixtures. Maleimide functionalities were incorporated into cresol novolac oligomers, and these were crosslinked with bisphenol-A epoxy. The processability of oligomers containing thermally labile maleimides were limited to lower temperatures. However, sufficiently high molecular weight oligomers were necessary to obtain good network mechanical properties. Networks prepared from 1250 g/mol cresol novolac containing maleimide functionilities and epoxy exhibited good network properties and could be processed easily. Latent triphenylphosphine catalysts which are inert at processing temperatures (~140°C) but possess significant catalytic activity at cure temperatures 180-220°C were necessary for efficient composite fabrication using phenolic novolac/epoxy matrix resins. Both sequestered catalyst particles and sizings were investigated for this purpose. Phenolic novolac/epoxy mixtures containing sequestered catalysts exhibited significantly longer processing time windows than those containing free catalysts. The resins also showed accelerated reaction rates in the presence of sequestered catalysts at cure temperatures. Trihexylamine salt of a poly(amic acid) was sized onto reinforcing carbon fibers and the composite properties indicated that fast phenolic novolac/epoxy cure could be achieved in its presence. / Ph. D.

Soil microorganisms are primarily limited by carbon (C) availability. The majority of C entering belowground food webs comes directly from local flora. Plant derived labile C compounds affect microbial community structure and function, which in turn drive ecosystem function. Research has focused on dissolved organic C (DOC) from litter leachates and root exudates. These compounds are often readily assimilable by soil microorganisms and are precursors for stable soil organic matter formation. Due to diffusion limitation DOC rarely travels far beyond its origin, meaning most soil microorganisms are unable to access these compounds unless they are located near the C source. However, recent studies have illuminated the importance of volatile organic compounds (VOCs) in soil ecosystems. VOCs are produced in abundance and, as vapors, they are able to travel through soil more rapidly than DOC. This dissertation aims to investigate the importance of VOCs commonly produced during the decomposition of leaf litter. We used three separate microcosm experiments to answer the following questions. 1) How do abundant VOCs affect microbial activity in soil? 2) How do VOCs affect nitrogen (N) transformations and the microbes associated with N transformations? 3) How do VOCs affect microbial community composition? 4) Are VOCs from decomposing litter incorporated into soil C pools? In chapter 2, we show that methanol and acetone – common litter derived VOCs – increase microbial activity and labile soil C, while also decreasing available nitrate, and ammonia oxidizing archaea. Interestingly, this decrease in nitrifiers did not affect nitrification rate after VOC addition was ceased. In chapter 3, we demonstrate that soil microbial taxa respond differently to DOC and VOCs at different soil moisture levels. Specifically, DOC primarily affected taxa abundance in wetter soils, while the insoluble VOC α-pinene had the largest impact at lower moisture levels, and methanol affected abundance at all moisture levels. Finally, in chapter 4, we demonstrate that VOCs from decomposing leaf litter altered soil bacterial and fungal communities, and VOC derived C entered all measured soil organic matter pools without direct contact between decomposing litters and the soil. This work demonstrates the importance of VOCs on soil microbial communities and ecosystem function. The VOC induced increase in microbial activity, and the effects of VOCs at low moisture levels suggest that VOCs may function in the bulk soil in a manner similar to DOC in rhizosphere soil. Additionally, the incorporation of VOC-C into soil organic matter pools identifies a hitherto unrecognized mechanism for soil organic matter formation. / Doctor of Philosophy / Soil microorganisms live in an environment where their access to carbon containing compounds limits their growth. In these belowground environments most of the carbon flows from aboveground plant matter through soil microbes into the organisms that consume those microbes. The carbon from plants not only feeds the soil microbes but also changes the type of microbes and how those microbes process important chemicals in the environment – e.g., carbon and nitrogen. Previously, research has focused on carbon compounds that are able to dissolve in water. Often, these compounds originate from liquids that plants release from their roots, or dissolve like tea when leaves are soaked in water. Soil microorganisms can often use these dissolved carbon compounds and directly incorporate them into their biomass. Additionally, these compounds can be stored in soil - sequestering that carbon in the soil, potentially long term. However, dissolved compounds are unable to move very quickly through soil, and the soil microorganisms that live far from the source of these compounds do not have access to them. However, recent studies have found that another form of carbon, volatile organic compounds, are also produced in abundance in the soil environment. These compounds can travel through the air in the soil, as well as in the soil water. When in the air, VOCs travel very quickly and can also travel farther than dissolved compounds. This dissertation aims to investigate the importance of volatile organic compounds that are produced during the decomposition of leaves. We carried out three experiments using small volumes of soil under controlled conditions in the laboratory. We aimed to answer the following questions. 1) How do abundant volatile organic compounds affect microbial activity in soil? 2) How do volatile organic compounds affect microbial processing of nitrogen containing compounds, and the populations of microorganisms that process those compounds? 3) How do volatile organic compounds affect the composition of microorganism in the soil? 4) Are volatile organic compounds from decomposing leaves able to be stabilized in the soil. In chapter 1, we show that methanol and acetone – common volatile compounds produced during the decomposition of leaves– increase microbial activity, and microbial available carbon in soil. Methanol and acetone also decreased available nitrate (an important N containing compound) and a group of organisms that produce nitrate called ammonia oxidizing archaea. Interestingly, once we stopped adding methanol and acetone to the soil the production of nitrate did not differ, meaning that the nitrate producing community was able to recover from the reduction in ammonia oxidizing archaea. In chapter 2, we demonstrated that soil microbial taxa respond differently to dissolved carbon and volatile organic compounds across a gradient of soil moisture. Specifically, dissolved carbon primarily affected taxa abundance in wetter soils, while the insoluble volatile α-pinene had the largest impact at lower moisture levels, and the volatile compound methanol affected abundance of microbial taxa at all moisture levels. Finally, in chapter 3, we demonstrate that volatile organic compounds produced during the decomposition of leaves altered the composition of both bacterial and fungal communities in the soil. Also, and possibly most interestingly, carbon from those volatile organic compounds was stored in all of the pools of carbon that we measured. Together these chapters demonstrate the importance of volatile organic compounds on soil microbial communities and ecosystem function. Since volatile organic compounds induced an increase in microbial activity we are able to infer that soil microorganisms are using these compounds; paired with our observation that volatile organic compounds affected microbial taxa at lower moisture levels than the dissolved compounds did, we can infer that volatile compounds may function as a carbon source in parts of the soil that do not have access to dissolved carbon. Additionally, the incorporation of carbon from volatile organic compounds into soil identified a hitherto unrecognized mechanism for soil carbon sequestration.

The components of soil CO2 efflux are affected by many soil properties including temperature, moisture, microbial abundance and activity, and other soil physical and chemical properties. Changes in these factors can result in high spatial and temporal variability of total soil CO2 efflux. Low molecular weight organic acids (LMWOAs), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), microbial biomass and activity were measured to evaluate the impact of intercropping switchgrass (Panicum virgatum L.) in a loblolly pine (Pinus taeda L.) plantation. Surface soil samples (0-15 cm) were collected on the bed (PSG-B), interbed (PSG-I) and edge (PSG-E) of pine-switchgrass intercropped treatments, as well as pine only (P-B) and switchgrass only (SG-I) treatments. Differences in most soil properties and processes of intercropped treatments were sporadic and most did not show clear trends. However, significant correlations between DOC, soil temperature, oxalic and acetic acids and soil CO2 efflux were present. In an multiple regression model these factors explained 57% of the variance in total soil CO2 efflux. Therefore we think that LMWOAs, as a labile component of DOC, are influencing total CO2 efflux because they are being consumed by microbial community, increasing heterotrophic respiration and as a result overall total CO2 efflux. The amount and distribution of labile C controls microbial community dynamics, heterotrophic respiration as well as the stabilization of soil C. / Master of Science

Crystallisation is gaining a lot of interest in pharmaceutical industry to help designing active ingredients with tailored physicochemical properties. Many factors have been found to affect the crystallisation process, including process parameters and material attributes. Several studies in the literature have discussed the role of these parameters in the crystallisation process. A comprehensive study is still missing in this field where all the significant terms are taken into consideration, including the square effect and the interaction terms between different parameters. In this study, a thorough investigation into the main factors affecting crystallisation of a polymeric system, processed via injection moulding, was presented and a sample of response optimisation was introduced which can be mimicked to suite a specific need. Three grades of pure polyethylene oxide; 20K, 200K and 2M, were first characterised using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) and shear rheometry. The onset of degradation and the rate varied according to molecular weight of polyethylene oxide (PEO). The peak melting temperature and the difference in enthalpy between melting and crystallisation were both in a direct proportion with PEO molecular weight. PEO200K and PEO2M struggle to recrystallise to the same extent of the original state at the tested cooling rates, while PEO20K can retain up to a similar crystallinity degree when cooled at 1 °C/min. Onset of crystallisation temperature (Tc1) was high for PEO2M and the difference between the 20K and 200K were pronounced at low cooling rate (20K is higher than 200K). The rheometer study showed that PEO2M has a solid-like structure around melting point which explains the difficulty in processing this grade at a low temperature via IM. PEO20K was almost stable within the strain values studied (Newtonian behaviour). For higher grades, PEO showed a shear thinning behaviour. The complex viscosity for PEO2M is characterised by a steeper slope compared to PEO200K, which indicates higher shear thinning sensitivity due to higher entanglement of the longer chains. For binary blends of PEO, the enthalpy of crystallisation studied by DSC was in direct proportion to the lowest molecular weight PEO content (PEOL %) in PEO20K/200K and PEO20K/2M blends. The effect of PEOL% on Tc1 became slightly pronounced for PEO20K-2M blends where Tc1 exhibited slight inverse proportionality to PEOL% and it became more significant for PEO200K-2M blends. It was interesting to find that Tc1 for the blends did not necessarily lie between the values of the homopolymers. In all binary blends, Tc1 was inversely proportional to cooling rate for the set of cooling rates tested. Thermal analysis using hot stage polarised light microscopy yields different behaviours of various PEO grades against the first detection of crystals especially where the lowest grade showed highest detection temperature. Visual observation of PEO binary blends caplets processed at various conditions via injection moulding (IM) showed the low-quality caplets processed at mould temperature above Tc1 of the sample. The factors affecting crystallisation of injection moulded caplets were studied using response surface methodology for two responses; peak melting temperature (Tm) and relative change in crystallinity (∆Xc%) compared to an unprocessed sample. Mould temperature (Tmould) was the most significant factor in all binary blend models. The relationship between Tmould and the two responses was positive non-linear at the Tmould ˂ Tc1. Injection speed was also a significant factor for both responses in PEO20K-200K blends. For Tm, the injection speed had a positive linear relationship while the opposite trend was found for ∆Xc%. The interaction term found in the RSM study for all models was only between the injection speed and the PEOL % which shows the couple effect between these two factors. Molecular effect was considered a significant factor in all ∆Xc% models across the three binary blends. The order of ∆Xc% sensitivity to the change in PEOL% was 3, 5 and 7 % for 20K-200K, 200K-2M and 20K-2M.

The behavior of the system consisted by mixture of two different molecular weight hyaluronates and surfactant was investigated. Mixtures were 17 kDa hyaluronate with 1,46 MDa, 73 kDa with 1,46 MDa, 300 kDa with 1,46 MDa, 806 kDa with 1,46 MDa and 1800 kDa with 1,46 MDa. These compounds were always mixed in the weight ratios 70:30, 50:50 and 30:70. As the surfactant cetrimonium bromide and TWEEN 20 were used. Interactions were studied in aqueous solution with different ionic strength. Sudan red was used as hydrophobic dye. In all experimental series with cetrimonium bromide was observed phenomenon of discontinuous separated phases, described as pearls. Samples containing pearls were tested on stability, were dried and rehydrated back, as were also heated in solution. Subsequently, the particle size was measured in the remaining sample after pearls were filtrated. Mixtures of hyaluronate were characterized by measuring the viscosity using rheology microrheology. It was found that these compounds are heterogeneous and each sample point is not the same viscosity.

In the recent past it has been found that a considerable pressure drop occurred during the extrusion of linear polyethylene in the course of capillary flow. The pressure drop resides within a narrow temperature window of one to two degrees Celsius. In this research the hydrodynamic condition and molecular origin of the extrusion window of linear polymer were investigated further. The advantage of the extrusion window, viz. smooth extrudate with less die swell ratio attained at low extrusion pressure and temperature, has potential in industrial applications. However, the extrusion window, corresponding to linear polyethylene (PE) with relatively low polydispersity (<7), has a narrow window temperature interval, circa 1~2°C, thus it could not be applied to industrial scale processing at the industrial scale. To have a fundamental insight and make the process industrially viable, research in this thesis was devoted to broaden the extrusion window to tolerate the thermal fluctuations in conventional processing. To achieve this goal molecular weight dependence of window temperature and flow criticalities is revealed. The hydrodynamic conditions of the extrusion window observed in a rate-controlled rheometer and stick-slip flow studied in a stress-controlled rheometer could be traced back to the same origin, viz. slip flow arises due to the disentanglement of adsorbed chains on capillary wall from free chains in the bulk. Secondly, a dual window effect was uncovered in the course of capillary flow of a bimodal PE, which is consistent with the window temperature dependence on molecular weight. Moreover, it was found that flow induced orientation within the window effect is even less than that observed in steady state flow at a relatively low shear rate. This implies that in the window region only relaxed free chains are extruded through the capillary die and most of the adsorbed chains, which could be disengaged from the entangled melt, remain sticking to the inner capillary wall. This observation is consistent with the hydrodynamic origin of high-surface-energy-die slip flow. Finally, a unimodal linear PE with extremely broad molecular weight distribution, i.e. polydispersity (PDI) is 27, showed a broad window effect, circa 8°C, at an appropriate apparent shear rate. The molecular origin of such a broad window effect is due to its broad molecular weight distribution. These results have further implications for energy efficient processing.