As fossil fuel usage has been proven to have a negative impact on human health and the environment, the world has embraced the usage of renewable energy sources, mainly for energy production. In Cyprus, solar energy is the most potent renewable source and this can be seen by the vast majority of the population using solar water heaters in their households. This thesis explores the usage of solar energy for electricity and domestic hot water production at a residential level by presenting the designs of three solar-thermal concept systems for achieving this task; the first being the basic design of all three without any form of storage, the second is fitted with thermal latent heat storage and the third is fitted with a natural gas boiler instead. The optimal solution is the second concept system that is capable of storing thermal energy around the year thus having a nearly uninterrupted operation, reducing the dependency on fossil fuel produced electricity and emissions. The thesis also explored the usage of siloxane organic compounds as working fluids for a low temperature Rankine cycle, which had a significant impact in the increase of the thermal-to-electrical efficiency of the cycle, raising it to nearly 25%, greater than the efficiency of best acclaimed photovoltaic collector currently available. Lastly, taking into account a typical household’s demand profile and by allowing the optimal system to operate as part of the national electrical network continuously, the size of the system’s components could be reduced significantly making it more feasible for installing in a typical household’s premises. However, due to the non-existence of these components in the within the project’s specifications, the thesis could not include a useful economic analysis for a more realistic comparison with a similar sized photovoltaic system.

Biological fouling occurs everywhere in the marine environment and is a significant problem for marine vessels. Anti-fouling coatings have been used effectively to prevent fouling; however, these coatings harm non-targeted sea-life. Fouling-release coatings (FRC) appear to be an alternative way to combat fouling. FRC do not necessarily prevent the settlement of marine organisms but rather allow their easy removal with application of shear to the coatings surface. These coatings must be non-toxic, non-leaching, have low surface energy, low modulus, and durability to provide easy removal of marine organisms. Here the goal is to develop FRC based on thermosetting siloxane-polyurethane, amphiphilic polyurethane, and zwitterionic/amphiphilic polyurethane systems. A combinatorial high-throughput approach has been taken in order to explore the variables that may affect the performance of the final coatings. Libraries of acrylic polyols were synthesized using combinatorial high-throughput techniques by either batch or semi-batch processes. The design of the experiments for the batch and semi-batch processes were done combinatorially to explore a range of compositions and various reaction process variables that cannot be accomplished or are not suitable for single reaction experiments. Characterization of Rapid-GPC, high-throughput DSC, and gravimetrically calculated percent solids verified the effects of different reaction conditions on the MW, glass transition temperatures, and percent conversion of the different compositions of acrylic polyols. Coatings were characterized for their surface energy, pseudobarnacle pull-off adhesion, and were subjected to bioassays including marine bacteria, algae, and barnacles. From the performance properties results the acrylic polyol containing 20% hydroxyethyl acrylate and 80% butyl acrylate was selected for further siloxane-polyurethane formulations and were subjected to the same physical, mechanical, and performance testing. Amiphiphilic copolymers based on PDMS molecular weight and the addition of PEG based polymer blocks on the properties of acrylic-polyurethane coatings were explored. The key properties screened were surface energy, determined by contact angle measurements using water and methylene iodide, dynamic water contact angle, and pseudobarnacle adhesion properties. The data from all of the biological assays indicates that the novel coatings were able to resist fouling and have low fouling adhesion for the broad variety of fouling organisms tested.

The first part of this research constituted the study of oligomeric incorporation into an inorganic network leading to the fonnation of a hybrid material by the sol-gel process. The oligomeric species chosen was silanol terminated poly(dimethylsiloxane) (PDMS) and the inorganic oxide precursor chosen was titanium tetra-isopropoxide (TIP). The rationale for choosing these materials stemmed from the desire to make materials for optical filters since a gradient of optical properties can be derived based on the composition and the initial reaction conditions. 29Si NMR studies were conducted to investigate the incorporation process which led to the conclusion that the PDMS chains were being degraded by the TIP. This problem led to the synthesis of TIP endcapped PDMS which was then used as the oligomeric component in the hybrid materials. The endcapping changed the functionality of the oligomer to six, and more importantly, its reactivity which was now closer to that of the TIP. Also, having the same functionality at the ends as the precursor affects the compatibility of the two components. Hybrid materials in the form of free standing films were fabricated from varying TIP/pDMS compositions and different initial reaction conditions. The hybrid materials synthesized were then subjected to a systematic structure-property relationship study. The degree of phase mixing or the encapsulation of the siloxane phase by the inorganic oxide increases with higher TIP content. This behaviour was seen by both the dielectric and dynamic mechanical studies. The modulus and the stress to break increased with higher TIP content while the strain to break decreased. At the 50/50 TIP/PDMS composition there was an abrupt change in the mechanical properties which signified a morphological change in these materials. The refractive indices of the materials also showed a trend similar to that of the mechanical properties. Three different cure procedures, viz., room temperature, thermal cure at 70 °C and microwave cure at 70 °C were utilized to fabricate the films. More phase separation occurred in the microwave cured over the thermally cured materials as evident from dielectric and dynamic mechanical studies. However, the effect diminished with higher TIP content in the materials. Changing the initial reaction conditions by varying the initial water and acid content changed the properties observed in the final products. Dielectric and dynamic mechanical studies showed that the phase separation was higher with increased water content. Also, the modulus of the materials made with increased water content was higher. Decreased acid content led to better dispersion of the two components as shown by the dielectric and dynamic mechanical experiments. The effect of using a less reactive inorganic component tetra-ethyl orthosilicate (TEOS), instead of TIP was also studied. The TEOS/pDMS materials showed more phase mixing than the TIPIPDMS materials, although, the dielectric tan δ peak maxima appeared at a lower temperature. The TEOS/PDMS materials were also less stiff than the TIP/PDMS materials. Structural studies were conducted by means of solid-state NMR, electron microscopy and small angle x-ray scattering (SAXS). With few exceptions, these studies correlated very well with the properties observed in these materials. The spin-lattice relaxation times obtained from the solid-state NMR correlated with the better phase mixing observed in the TEOSIPDMS materials relative to the TIPIPDMS materials. Electron microscopy in the backscattered mode showed the presence of microphase separation in these materials. At the 50/50 TIPIPDMS composition connectivity of the inorganic oxide phase was complete, perhaps encapsulating the siloxane phase totally. Microstructural differences were observed due to the variation in the cure modes. The domain sizes of the oxide phase were finer in the thermally cured as compared to the room temperature cured materials. Higher water content led to a very different microstructure when compared to materials made with lower water content. Smaller spherical particulate type structures were observed in the material made with higher water content. The domain sizes of the oxide phase in the TEOS/PDMS material were bigger than those in the TIP/PDMS material of equivalent composition. These differences may be intimately related to the reactivity difference between TIP and TEOS. The SAXS data supported the microstructure seen by electron microscopy and the properties observed by dynamic mechanical, dielectric and mechanical studies. / Ph. D.

Novel, polyand weight, randomly coupled, poly(imide siloxane) segmented copolymers were prepared and characterized. The copolymers were synthesized in two steps, the first involving the generation of soluble poly(amic acid) intermediates through reaction of various aromatic dianhydrides and aromatic diamines with a series of bis(aminopropyl)polydimethylsiloxane oligomers. These difunctional siloxane oligomers were prepared through the anionic equilibration of octamethylcyclotetrasiloxane with bis(3-aminopropyl)tetramethyldisiloxane in the presence of a siloxanolate catalyst. The aromatic monomers and siloxane oligomers were quantitatively reacted in a cosolvent system. The poly(amic acid) intermediates were then cyclodehydrated employing two different thermal treatments to afford the imidized homo- and copolymers. The first imidization process, conducted on solution cast poly(amic acid) films, employed stepwise heating cycles to 300°C. Quantitative thermal imidization was also achieved in solution at temperatures in the 140 to 170°C range. This novel method of imidization used a coamide solvent system. Kinetic studies employing FTIR indicated that the imidization process could be described by first order kinetics. An activation energy of 26 kcal/mole (109 kj/mole) was derived. The homopolymers and siloxane modified copolymers were characterized as a function of chemical composition and imidization method. Polymer solubility and processability greatly improved upon siloxane oligomer incorporation and the use of the solution imidization procedure. Regardless of the method of imidization, all homo- and copolymers possessed excellent thermal, mechanical, and adhesive properties. These properties were found to be a function of siloxane content and siloxane oligomer molecular weight. In all segmented copolymer systems, a two-phase microstructure developed at relatively low block molecular weights. X-ray photoelectron spectroscopy (XPS) results indicated that the surface of copolymer films was largely dominated by siloxane. Because of this, the siloxane modified copolymers advantageously displayed lower water uptake and much improved resistance to oxygen plasma degradation. XPS and SEM studies showed that the stabilization mechanism involved a siloxane to silicate transformation under an oxygen plasma environment. / Ph. D.

Novel, high molecular weight, high glass transition temperature, photocrosslinkable polyimide and poly(imide siloxane) homo- and segmented copolymers were prepared and characterized. The polyimides were synthesized by the classical two step method of first preparing soluble poly(amic acid) prepolymers by the reaction of various aromatic dianhydrides with aromatic diamines. The siloxane modified copolymers were synthesized by reacting single or mixed components of the aromatic dianhydrides with a mixture of aromatic amine and bis(3-aminopropyl) end blocked polydimethyl siloxane oligomers in a cosolvent system of tetrahydrofuran and N-methyl-2-pyrrolidinone. These dysfunctional aminopropyl terminated siloxane oligomers were prepared through an anionic ring opening equilibration polymerization of octamethylcyclotetrasiloxane with bis(3—aminopropyl) tetramethyldisiloxane in the presence of siloxanolate catalyst. Soluble fully imidized polyimides were obtained by use of a solution imidization procedure which utilized a cosolvent system of N-methyl-2-pyrrolidinone and N-cyclohexyl-2-pyrrolidone at temperatures of approximately 170°C. The fully imidized polyimides were soluble in a variety of solvents. The homo- and copolymers have been characterized for compositional analysis by FT-IR and proton NMR spectroscopy. All polymers were characterized for their thermal properties by differential scanning calorimetry, dynamic mechanical thermal analysis and thermogravimetric analysis. All homoand copolymers possessed excellent thermal characteristics and good mechanical properties. The photosensitive properties of the polyimide and poly(imide siloxane) homo- and copolymers were investigated at the UV wavelengths of 313nm and 365nm. The photosensitivities were found to depend on both the amount of benzylic methyl substituted diamine incorporated into the polyimide backbone, and the amount of aromatic ketone concentration. High concentrations of fluorinated (6F) dianhydride were also desirable. Incorporation of the polydimethylsiloxane segments into the polyimide decreased the optical density without decreasing the photosensitivity and therefore desirably allowed thicker films to be crosslinked at lower exposure doses. The adhesion of the siloxane modified polyimides to the silicon wafers was increased with significantly increasing siloxane content and at 20 weight percent, eliminated the need for conventional coupling agents. / Ph. D.

The synthesis of organosiloxanes via equilibration processes is fairly well known, but relatively little is known about the detailed kinetics and mechanisms involved, particularly in the presence of functional endblockers. A major focus of the present study was to investigate aspects of the kinetics of siloxane equilibration polymerizations in the presence of 1,3-bis(3-aminopropyl) tetramethyldisiloxane. Catalysts studied included the commonly used potassium siloxanolate catalyst, as well as the analogous tetramethylammonium and tetrabutylphosphonium siloxanolate catalysts. The reactions of the quaternary ammonium and phosphonium systems were limited to about 80°C due to the known transient nature of those species at elevated temperatures. The rates of disappearance of the cyclic tetramer D₄ and aminopropyl disiloxane were monitored through the use of HPLC and GC techniques. The results indicated that the ammonium and phosphonium catalysts were much more efficient at early incorporation of the aminopropyl disiloxane into the oligomer. By contrast, studies using the potassium siloxanolate catalyst were less effective, even at much higher temperatures such as 160°C. The explanations for this behavior may be related to the higher degree of dissociation and possibly enhanced solubility of the ammonium and phosphonium systems relative to the more studied potassium system. The significance of these results with respect to functional siloxane systems has not been previously appreciated. Kinetic results indicated that the apparent rates are proportional to the square root of the catalyst concentration, in agreement with earlier studies on the potassium catalyst in nonfunctional siloxane systems. The reaction order with the bulky tetrabutylphosphonium catalyst was slightly higher, again indicating a more dissociated active siloxanolate species. Despite the rate differences, the same equilibrium number average molecular weight was obtained, regardless of catalyst concentration. The effect of catalyst is manifested mainly in the rate at which equilibrium is reached. Supercritical fluid fractionation studies of the functional siloxanes were demonstrated to be quite feasible. Relatively narrow molecular weight distribution fractions were obtained when compared with polysiloxane standards synthesized via the organolithium initiated polymerization of the cyclic trimer. Excellent agreement was realized between the molecular weight values determined by titration of the amine endgroups and those calculated by GPC. Additional aspects of this study included the preparation of alkyl-substituted polyarylesters and polyformals, and modification of these materials with polydimethylsiloxanes. Tough transparent films were readily solution cast from these materials, which may have potential use as permselective gas separation membranes. Due to the intentionally short segment lengths, evidence of significant amounts of phase mixing was observed by DSC and TEM. / Ph. D.

Ce travail présente une étude de procédé de traitement des siloxanes et de l’H2S appliqué à la purification des biogaz. Une approche bibliographique montre l’intérêt de développer de nouveaux procédés de traitement à faible coût pouvant s’intégrer facilement dans une filière complète de purification des biogaz. Une partie de l’étude est consacrée aux possibilités de traitement par transfert gaz-liquide dans des huiles. Cette technique est comparée à un procédé plus classique de traitement par adsorption sur charbon actif. Les résultats ont montré que ces 2 techniques étaient complémentaires, l’absorption dans une huile utilisée pour le traitement de fortes concentrations et l’adsorption sur charbon actif en traitement definition. Une autre partie de l’étude a été consacrée au traitement de l’H2S. Les niveaux d’abattement requis étant de plus en plus bas, l’approche choisie est celle d’un traitement definition en complément des traitements principaux classiques. Le procédé étudié est celui d’un système par physi-adsorption sur charbon actif en tissu pre-humidifié. Celui-ci est régénéré in situ par chauffage électrique direct et mise en dépression du réacteur. L’étude des conditions opératoires a permis d’établir des paramètres de régénération et des conditions de traitement permettant de réaliser des cycles pérenne. L’intérêt réside ici dans les conditions douces de température et de pression utilisées pour la régénération. / This work presents a study of the siloxanes and hydrogen sulfide separation process applied to the biogas treatment. A bibliography review shows the interest in the development of new technologies of low cost, to integrate them into an overall process of biogas up-grading. One part of this study is focused on the possible separation process by gas-liquid transfer into oils. This technology is compared with a more classical treatment process by adsorption into activated carbons. The results showed that both technologies are complementary, the absorption into oils used primarily to the abatement of high concentrations and the adsorption into the activated carbon as a finishing process. A second part of this study is focused on the hydrogen sulfide treatment. The requirements of abatement are very low, thus the approach is focused on a finishing process to complement the more classical methods. Thus a system by physic adsorption into pre-humidified activated carbon cloth was studied. The filter was regenerated in situ by direct electric heating under vacuum pressure. The study of the operating conditions allowed establishing the regeneration parameters and the process sustainability. The interest here is focused on the soft conditions of temperature and vacuum used to achieve the regeneration.

Ce travail présente une étude de procédé de traitement des siloxanes et de l'H2S appliqué à la purification des biogaz. Une approche bibliographique montre l'intérêt de développer de nouveaux procédés de traitement à faible coût pouvant s'intégrer facilement dans une filière complète de purification des biogaz. Une partie de l'étude est consacrée aux possibilités de traitement par transfert gaz-liquide dans des huiles. Cette technique est comparée à un procédé plus classique de traitement par adsorption sur charbon actif. Les résultats ont montré que ces 2 techniques étaient complémentaires, l'absorption dans une huile utilisée pour le traitement de fortes concentrations et l'adsorption sur charbon actif en traitement definition. Une autre partie de l'étude a été consacrée au traitement de l'H2S. Les niveaux d'abattement requis étant de plus en plus bas, l'approche choisie est celle d'un traitement definition en complément des traitements principaux classiques. Le procédé étudié est celui d'un système par physi-adsorption sur charbon actif en tissu pre-humidifié. Celui-ci est régénéré in situ par chauffage électrique direct et mise en dépression du réacteur. L'étude des conditions opératoires a permis d'établir des paramètres de régénération et des conditions de traitement permettant de réaliser des cycles pérenne. L'intérêt réside ici dans les conditions douces de température et de pression utilisées pour la régénération.

In vitro cell culture is an essential part of many cell and tissue engineering approaches. In particular, monolayer culture of mammalian cells is a key tool for applications such as cell therapy. Novel bioreactors like the Cellerator(TM) allow for expansion of cell populations on mechanically stimulated surfaces coated with proteins. This thesis constitutes a preliminary study which focused on cell-matrix interactions in the absence of stretch. The aim was to establish standard protocols for protein coating on poly (dimethyl siloxane) (PDMS) and for measuring cell proliferation. Specifically, the proliferation of rat pulmonary artery vascular smooth muscle (PAC1) cells on type I collagen and soluble fibronectin was studied. Growth curves were obtained and the doubling time for subconfluent cultures was computed. Although cell-matrix interactions do not enhance proliferation of PAC1 cells, it was found that a preliminary sulphuric acid treatment is necessary to yield a well-behaved culture.

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