While theoretical treatments of liquid spreading on solid surfaces can be found in abundance in the literature, relatively few experimental studies have been performed. This study focused on the experimental detection of polydimethylsiloxane spreading on polymer surfaces in the spreading regime where gravitational and inertial forces are negligible. The techniques of x-ray photoelectron spectroscopy (XPS), reflection absorption spectroscopy (RAS), and contact angle analysis were used to investigate this problem. XPS analysis indicated that the surface spreading or "creeping" was very slow, moving only several centimeters per several hundred hours in some cases. An interesting observation was that the spreading film seemed to reach a "steady state" concentration when covering an area. Similar results were seen for both horizontal and vertical substrate surfaces with XPS, and there seemed to be a substrate dependence. Angular-dependent XPS analysis revealed that the film was very thin (<20A) and not a complete layer. Contact angle analysis was used to monitor the siloxane movement, although there was a contact angle dependence on x-ray exposure time, indicating cross-linking of the surface film. Contact angle variations were also used to show that the film characteristics may be dependent on the nature of the polymer substrate. Reflection absorption spectroscopy was used to investigate thin substrate polymer films, and it was shown that theoretical predictions of absorption band intensity correlated reasonably well with the experiment. This technique was also used to investigate the surface siloxane layer and indicated that under some conditions, the orientation of the surface silicone layer may be occurring. / M.S.

The interaction of water vapor with the surface and bulk of poly(imidesiloxane) copolymers has been characterized in an attempt to determine the important factors in the copolymer's resistance to water ingression. The multi-block copolymers were synthesized from benzophenone tetracarboxylic dianhydride, bisaniline P and pre-formed amine-terminated poly(dimethylsiloxane) oligomers, with phthalic anhydride as an end-capping agent. Similar copolymers had been previously shown to have reduced water sorption, increased surface hydrophobicity, and increased adhesive durability in hot/wet environments. Inverse gas chromatography was used to conduct surface energetics studies on copolymers of different siloxane concentration and a polyirnide homopolymer. Free energies of specific interaction of water vapor, ΔG_sp°, with the polymer surfaces were found to decrease with the incorporation of siloxane into the polyirnide. The dispersive components of the solid surface free energy of the siloxane- containing copolymers were equal within error to that of pure poly(dimethylsiloxane), indicating a PDMS-rich, hydrophobic surface. The ΔG_sp° of the copolymers were not significantly different, suggesting that the copolymer surfaces were very similar. This indicated a minimum weight percent of siloxane incorporation required to maximize the copolymer's surface water resistance. The minimum amount for the studied system was at most ten percent. Diffusion coefficients of water vapor in the polyimide and copolymers were determined from gravimetric sorption experiments. Higher levels of siloxane incorporation caused a definite increase in the diffusion coefficient, indicating a decreased resistance to water ingression. The increase in diffusion was found to be influenced by siloxane block length and was interpreted in terms of morphological and free volume theories. The diffusion coefficient of a 10 weight percent PDMS copolymer, however, was found to be the same within error as the polyimide diffusion oefficient. The incorporation of siloxane into polyimides has been shown to increase water resistance due to the hydrophobicity of the siloxane-rich surface. However, high siloxane contents also increased the rate of water ingression in the bulk of the polymer. Increased water resistance of the surface may be achieved at lower siloxane concentrations without increasing diffusive (or decreasing mechanical) properties to undesirable levels. / Ph. D.

Le biogaz issu de la dégradation anaérobie de matières organiques peut remplacer le gaz naturel dans plusieurs applications. Pour une meilleure valorisation énergétique du biogaz, ce travail s’intéresse à l’élimination des composés organiques volatils du silicium (siloxanes) dans biogaz par l’adsorption sur des matériaux poreux. Trois charbons actifs (CA) commerciaux ont été utilisés pour l’adsorption des siloxanes. Leurs propriétés physicochimiques sont caractérisées par plusieurs techniques. Un CA montre excellent capacité d’adsorption d’octaméthylcyclotétrasiloxane (D4) ce qui est bien supérieur que l’autre. En présence de la vapeur, les capacités d’adsorption des CA peuvent être réduites plus ou moins fort dépendant de dégrée d’humidité relative et la présence des sites hydrophiles sur la surface de CA. Ainsi, la capacité des échantillons possédant ces sites spécifiques est réduite après la thermodésorption à cause de la formation des espèces non volatiles sur la surface de CA. Tests avec d’autres siloxanes ont montré que le phénomène de polymérisation s’est produit avec de réactivité et de mécanisme différent, dépendant de la nature du CA et de siloxane. La polymérisation est toujours plus importante pour le CA qui présent plus de sites hydrophiles, conduisant également à sa plus faible régénérabilité / Biogas issued from the anaerobic digestion of organic materials is a renewable energy source that can replace natural gas in many applications. For a better energy recovery of biogas, this work focuses on the elimination of the volatile organic compounds of silicon (siloxanes) in biogas by the adsorption onto porous materials. Three commercial activated carbons (CA) were used for the adsorption of siloxanes. Their physicochemical properties are characterized by several techniques. Measurement of adsorption capacity of octamethylcyclotetrasiloxane (D4) revealed a CA that works better than the others. In presence of water vapor, the adsorption capacities of all AC can be reduced more or less depending on the degree of relative humidity and the presence of the hydrophilic sites on the surface of AC. Also, D4 adsorption capacity of samples with these specific sites is reduced after thermodesorption due to formation of nonvolatile species on the surface of AC. Tests with other siloxanes showed that the polymerization phenomenon occurred with different reactivity and mechanism, depending on the nature of the CA and siloxane. The polymerization is always more important for the CA which has more hydrophilic sites, thus leading to its lower regenerability

Afin de satisfaire la demande croissante des systèmes de traitement de l'air, des procédés commerciaux basés sur la photocatalyse par TiO2 ont été commercialisés. Récemment le problème de la désactivation de ces systèmes a attiré l'attention des industriels ainsi que des chercheurs. Les Siloxanes Méthyliques Volatils (SMVs) présents dans l'air auraient été identifiés comme une source majeure contribuant à cette désactivation. Par ailleurs, dans les centres de stockage des déchets, la valorisation du biogaz nécessite de recueillir et de traiter le biogaz issu des déchets organiques en vue de produire de l'énergie renouvelable et inoffensive pour l'environnement. A nouveau, les SMVs ont été identifiés comme un frein principal au développement de cette filière, ces derniers conduisant après oxydation à des dépôts de silice abrasifs dans le moteur. Les difficultés de mesure des SMVs aussi bien dans le biogaz que dans l'air ambiant ainsi que l'évaluation de leur impact sur les systèmes photocatalytiques ou dans les procédés de valorisation du biogaz constituent par conséquent un vrai défi. Afin de répondre à ces problématiques, ce travail comporte trois volets principaux : Le premier volet est dédié à la mise au point d'une méthode de mesure des siloxanes méthyliques volatils dans le biogaz et dans l'air ambiant. Pour ce faire nous avons choisi de mettre en place un système d'échantillonnage des SMVs basé sur leur piégeage et préconcentration sur un support solide suivi d'une désorption thermique ou chimique (extraction par solvant) avant leur analyse par GC-MS. Puisqu'aucune étude systématique sur le choix des supports n'est relatée dans la littérature, nous avons comparé plusieurs types d'adsorbants en déterminant le volume de perçage pour chacun des SMVs afin de choisir le (les) meilleur(s). Le second volet est consacré à l'évaluation des teneurs en SMVs dans le biogaz ainsi que dans l'air ambiant en différents endroits. Une méthode d'analyse des SMVs fiable a été développée qui a permis de confirmer les résultats précédents obtenus au laboratoire en ce qui concerne le choix des adsorbants pouvant piéger quantitativement les SMVs. Enfin, dans le troisième volet, l'impact des SMVs sur les systèmes photocatalytiques en choisissant comme molécule modèle l'octaméthylcyclotétrasiloxane (D4) a été étudié / In order to address the growing demand for indoor air treatment, many commercial systems based in the potocatalytic degradation using TiO2 have reached the market. Recently, deactivation of these systems has been observed. Some of the potentially most important deactivation pollutants are volatile methyl siloxanes (VMS), which are becoming more and more abundant indoor and in ambient air. Moreover, the increasing interest in the utilization of biogas to generate renewable energy (production of heat or electricity), has created significant concerns about the presence of VMS in the biogas. During biogas combustion, VMS are oxidized to abrasive microcrystalline silica that causes serious damage to gas engines, thus reducing the economic benefits of using biogas. Hence, it is essential to be able to measure the concentration of such VMS in ambient air and in biogas by a reliable method, as well as to study their impact on the photocatalytic systems. To address these issues, this work has three main parts: The first part is dedicated to the development of a method for measuring volatile methyl siloxanes in biogas and in ambient air. We have chosen sampling gas through sorbent tube followed by thermal desorption or chemical desorption (solvent extraction) and analysed using GC-MS. Since no systematic study on the choice of materials is related in the literature, we compared several types of adsorbents based on the determination of the VMS breakthrough volume (BV), in order to choose an appropriate adsorbent and to obtain accurate quantification of VMS. The second part is devoted to the evaluation of VMS in biogas and in ambient air at different sites. A reliable analytical method has been developed, and results are in agreement with the previous results obtained in the laboratory regarding the choice of adsorbents. Finally, in the third part, for a better understanding of the impact of VMS on photocatalytic systems, D4 was chosen as a VMS model compound as it is one of the most important VMS

In high performance electronic systems, with increasing chip speed and larger number of processors, the system performance is being limited by off-chip metal interconnects. In such systems, polymer optical waveguides are being considered to replace electrical interconnects because of their high capacity for bandwidth and less constraints on interconnect length. The optical loss in the polymer optical waveguides is the key criterion used to evaluate their performance, and is significantly affected by thermal curing and aging. The evolution of degree-of-cure is determined from differential scanning calorimetry and compared to optical absorption from spectroscopy. Optical loss due to scattering mechanisms is related to local density fluctuations, which is studied using dielectric analysis. Based on the optical loss trends in uncladded and cladded waveguides, the underlying mechanisms for the optical loss variations are proposed and a cure process schedule to realize the lowest optical loss is recommended. Process-induced thermal stresses can also affect the polymer waveguide by introducing stress birefringence. The stress-optical coefficients of the siloxane polymer are extracted and employed in a numerical modeling method to determine the stress-induced birefringence in an optical waveguide system. The thermal-aging dependent optical loss is determined for waveguide samples at several different accelerated temperature conditions. To get the field-use conditions, the temperature distribution in the vicinity of the embedded laser and the polymer waveguide is determined. Using such thermal experimental data, the analytical reliability models were employed to relate the optical loss with time, and provide a practical way of determining whether the optical waveguides would perform within the optical loss budget during field-use conditions.

The aim of this study was to develop an analytical method for fluorinated silanes. Furthermore, as a secondary aim, to explore if there would be possible to detect 1H,1H,2H,2H-perfluorooctyl triethoxysilane (6:2 PTrEtSi) and 1H,1H,2H,2H-perfluorodecyl triethoxysilane (8:2 PTrEtSi) in two different matrices, sludge and cosmetic extract. The method development included experiments using LC-MS, LC-MS/MS, UPC2, GC-MS and APGC-MS/MS and was carried out using standards containing 6:2 PTrEtSi and 8:2 PTrEtSi. The analytical method that worked best for the compounds was GC-MS/MS and an analytical method using APGC-MS/MS was developed for fluorinated silanes. The IDL for 6:2 PTrEtSi was 0.0012 μg/mL and 1.32 μg/mL for 8:2 PTrEtSi. This makes the developed method suitable for high contaminated samples, such as extracts from cosmetic products. It was concluded that a method using LC as the analytical instrument would not work for the two target compounds since they were too reactive with the mobile phase. However, LC could be a good choice for siloxanes, compounds that are formed from hydrolysis and condensation of fluorinated silanes. The samples analyzed in this study were three sludge extracts and one extract from a cosmetic product. 6:2 PTrEtSi was expected to be detected in the cosmetic sample since the compound was stated on the table of contents of the cosmetic product. No detection of 6:2 TrEtSi or 8:2 TrEtSi could be made in either of the samples. The reason for this was suspected to be transformation or degradation of the compounds into other compounds. Therefore, a full scan of the cosmetic sample using LC-MS/MS was included in the experiment as an addition to verify the suspicions that compounds such as siloxanes could have been formed. An interesting peak was discovered with m/z 947 which could be a disiloxane of 6:2 PTrEtSi.

Durch die Insertion von CO2 in die Si-N-Bindung von Diaminosilanen sind Di(carbamoyloxy)silane zugänglich. Mittels thermischer Zersetzung dieser Insertionsprodukte können Siloxane und entsprechende Harnstoffderivate erhalten werden. In dieser Arbeit wurden die chemischen Reste in diesen Systemen variiert um Siloxane mit verschiedenen Substitutionsmustern zu erhalten. Außerdem wurde das Substituentenaustauschverhalten des System Aminosilan/Carbamoyloxysilan näher untersucht. Dabei konnte die Substanzklasse der Amino(carbamoyloxy)silane nachgewiesen werden. Auch die Adaption der Versuche auf Triaminosilane und Aminodisilane wurde erfolgreich durchgeführt. Dadurch wurden vernetzte Siloxane als Thermolyseprodukte erhalten. Einige Carbamoyloxydisilane bilden zudem fünffach koordiniertes Silicium aus.:Vorwort 1. Einleitung und Motivation 2. Literaturteil (Siloxane/Silikone und Harnstoffe) 3. Diaminosilane 4. CO2-Insertion in Diaminosilane - Synthese von Di(carbamoyloxy)silanen 5. Thermolyse 6. Triaminosilane und Tri(carbamoyloxy)silane 7. Aminodisilane und Carbamoyloxydisilane 8. Zusammenfassung und Ausblick 9. Experimenteller Teil 10. Anhang