Mainz, University, Diss., 2001.

Passive air sampling techniques are an attractive alternative to active air sampling because of the lower costs, simple deployment and retrieval methods, minimum training requirements, no need for power sources, etc.. Because of their advantages, passive samplers are now widely used not only for water and indoor, outdoor and workplace air analysis, but also for soil-gas sampling required for various purposes, including vapor intrusion studies, contamination mapping and remediation. A simple and cost effective permeation-type passive sampler, invented in our laboratory, was further developed and validated during this project. The sampler is based on a 1.8 mL crimp-cap gas chromatography autosampler vial equipped with a polydimethylsiloxane (PDMS) membrane and filled with a carbon based adsorbent. Apart from the low material costs of the sampler and ease of fabrication, the design allows for potential automation of the extraction and chromatographic analysis for high-throughput analysis. The use of highly non-polar PDMS reduces water uptake into the sampler and reduces early adsorbent saturation. The thermodynamic properties of PDMS result in moderately low sampling rate effects with temperature variations. Further, the use of PDMS allows for easy estimation of the uptake-rates based on the physicochemical properties of the analytes such as retention indices determined using capillary columns coated with PDMS stationary phase. In the thesis, the theoretical and practical aspects of the new design with regards to uptake kinetics modeling and the dependence of the calibration constants on temperature, humidity, linear flow velocity of air across the sampler surface, sampler geometry, sampling duration, and analyte concentrations are discussed. The permeability of polydimethylsiloxane toward various analytes, as well as thermodynamic parameters such as the energy of activation of permeation through PDMS membranes was determined. Finally, many applications of the passive samplers developed in actual field locations, vital for the field validation and future regulatory acceptance are presented. The areas of application of the samplers include indoor and outdoor air monitoring, horizontal and vertical soil-gas contamination profiling and vapour intrusion studies.

Passive air sampling techniques are an attractive alternative to active air sampling because of the lower costs, simple deployment and retrieval methods, minimum training requirements, no need for power sources, etc.. Because of their advantages, passive samplers are now widely used not only for water and indoor, outdoor and workplace air analysis, but also for soil-gas sampling required for various purposes, including vapor intrusion studies, contamination mapping and remediation. A simple and cost effective permeation-type passive sampler, invented in our laboratory, was further developed and validated during this project. The sampler is based on a 1.8 mL crimp-cap gas chromatography autosampler vial equipped with a polydimethylsiloxane (PDMS) membrane and filled with a carbon based adsorbent. Apart from the low material costs of the sampler and ease of fabrication, the design allows for potential automation of the extraction and chromatographic analysis for high-throughput analysis. The use of highly non-polar PDMS reduces water uptake into the sampler and reduces early adsorbent saturation. The thermodynamic properties of PDMS result in moderately low sampling rate effects with temperature variations. Further, the use of PDMS allows for easy estimation of the uptake-rates based on the physicochemical properties of the analytes such as retention indices determined using capillary columns coated with PDMS stationary phase. In the thesis, the theoretical and practical aspects of the new design with regards to uptake kinetics modeling and the dependence of the calibration constants on temperature, humidity, linear flow velocity of air across the sampler surface, sampler geometry, sampling duration, and analyte concentrations are discussed. The permeability of polydimethylsiloxane toward various analytes, as well as thermodynamic parameters such as the energy of activation of permeation through PDMS membranes was determined. Finally, many applications of the passive samplers developed in actual field locations, vital for the field validation and future regulatory acceptance are presented. The areas of application of the samplers include indoor and outdoor air monitoring, horizontal and vertical soil-gas contamination profiling and vapour intrusion studies.

Polydimethylsiloxane(PDMS) thin films have the advantages of flexible , good chemicophysical properties , low energetic surface that supports the vertical anchoring of liquid crystal molecules , could be fabricated easily by Replica Molding Method , low cost and good optically transparent. We study of the use of PDMS in flexible liquid crystal displays and the Electro-Optical properties of LC flexible cell. In experiment we use PDMS to fabricate vertical alignment layer , elastomer substrate and spacer to maintain the Electro-Optical properties in flexible displays.

In situ passive sampling is the use of a polymer sorbent to directly assess freely dissolved concentration (C [subscript free]) profiles within the environment. The primary focus herein is the use of passive sampling methods to detect and quantify persistent hydrophobic organic compounds (HOCs) in sediment porewater and surface water using solid phase microextraction (SPME) profilers with polydimethylsiloxane (PDMS) as the receiving phase sorbent. Contaminated sediment sites pose a unique challenge in terms of remediation and monitoring for several reasons including: the large number of past and ongoing sources, sediment stability, and the extent of contamination. Capping with a clean layer of material, an accepted remediation approach, can reduce risk by stabilizing the underlying sediments, isolating the water column, and reducing contaminant flux. Evaluating cap performance is challenging due to the long time frames associated with migration of HOCs. Additionally, the non-sorbing nature of most caps limits the usefulness of bulk solid measurements. An alternative is the use of concentrations in the interstitial space or porewater to examine contaminant migration in the sediments and cap. Traditionally, porewater concentrations are obtained through a conversion of bulk sediment concentrations using an assumed sediment-water partitioning coefficient. This assumption often leads to a misrepresentation of risk as not all organic carbon is created equal. An alternative is the use of passive sampling with polymer sorbents to estimate the freely available concentration, C [subscript free]. In this work the focus is on the use of solid phase microextraction with polydimethylsiloxane (SPME PDMS) as the sorbent. C [subscript free] is proportional to chemical activity; therefore an accurate measurement of C [subscript free] is necessary for risk assessment and determination of transport mechanisms and ultimately improved management of contaminated sediment sites. A non-equilibrium correction protocol using performance reference compounds (PRCs) was developed to enhance the accuracy of the SPME PDMS method to assess C [subscript free]. The protocol was validated through laboratory experiments and field trials. Deployment times can be reduced without sacrificing accuracy when using the PRC protocol. Furthermore, it was shown that mathematical models of diffusive and advective flux can be fit using parameters determined from PRC desorption. The SPME PDMS with PRCs method was used at three different remediated contaminated sediment sites, Chattanooga Creek, Eagle Harbor, and the West Branch of the Grand Calumet River, to illustrate its utility at evaluating performance of in situ remediation. Overall, the results from laboratory and field studies suggest that SPME PDMS is a valuable tool for evaluating performance of in situ sediment remediation. / text

No description available.

Universiẗat, Diss., 2006--Würzburg.

Würzburg, Univ., Diss., 2002.

No description available.

Für die definierte und konstante Wirkstofffreigabe aus therapeutischen Systemen sind Kenntnisse der Mikrostruktur vonKontrollmembranen von großer Bedeutung. Durch eine Additionsreaktion können Polydimethylsiloxan-Membranen ausvinylendgestoppten linearen Polydimethylsiloxanen und niedermolekularen Si-H-funktionalisierten Polydimethylsiloxanen unterEinfluss eines Platin- Katalysators hergestellt werden. Hierbei ist es durch den Einsatz genau charakterisierterAusgangspolymere möglich, Membranen mit einer statistisch definierten Mikrostruktur zu erhalten. Die Mikrostruktur kanndurch die Netzbogenlänge charakterisiert werden. Der Abschnitt zwischen zwei Verknüpfungspunkten in einem Netzwerk wirdals Netzbogenlänge (NBL) bezeichnet. Diese beschreibt die Anzahl der Dimethyl-siloxan-Einheiten zwischen zweiVerknüpfungen. Die Permeationseigenschaften wurden mit Hilfe des standardisierten Permeationskoeffizienten untersucht. Derstandardisierte Permeationskoeffizient ist von der mittleren Netzbogenlänge der Polydimethylsiloxan-Membranen abhängig. Dieser Zusammenhang wurde an elf Benzoesäure- und Naphthalinderivaten als Modellsubstanzen untersucht und bestätigt.Hierbei wurden Membranen mit den mittleren Netzbogenlängen 65, 99 und 122 Siloxan-Einheiten für die Untersuchungeneingesetzt. Bei allen untersuchten Substanzen stieg der Permeationskoeffizient mit größer werdender Netzbogenlänge derMembranen geringfügig an. Die Permeationskoeffizienten von Membranen mit der Netzbogenlänge 122 waren dabei - mitlediglich vier Ausnahmen - stets statistisch signifikant größer als von Membranen mit der Netzbogenlänge 65. Als mögliche weitere Einflussfaktoren auf die Permeationsgeschwindigkeit wurden der Membran/Wasser-Verteilungskoeffizient, dasDipolmoment und das van der Waals-Volumen der elf Modellsubstanzen untersucht. Es konnte ein Zusammenhang zwischendem Membran/Wasser-Verteilungskoeffizienten und dem Permeationskoeffizienten aufgezeigt werden. Das Volumen deruntersuchten permeierenden Moleküle hat jedoch nur bei Netzbogenlängen kleiner als 122 einen Einfluss auf diePermeationsgeschwindigkeit. Als neue Möglichkeit zur Untersuchung der Diffusionskinetik vor Erreichen des stationärenZustands in Polydimethylsiloxan-Membranen wurde die konfokale Raman-Spektroskopie eingesetzt. Bei derRaman-Spektroskopie wird das Probensystem während der Messung weder zerstört noch verändert. Weiterhin ist es möglich,durch das gekoppelte konfokale Mikroskop gezielt an einem bestimmten Punkt innerhalb der Membran zu messen. Damitkönnen nun dynamische Vorgänge wie der Aufbau eines Konzentrationsgradienten vor Erreichen des stationären Zustandes aneinem bestimmten Punkt in einer Membran über einen längeren Zeitraum gemessen werden. Anhand von Intensitätsänderungencharakteristischer Peaks oder der Verschiebung von Banden werden Konzentrations- und Strukturänderungen der Membranund der permeierenden Moleküle sichtbar. Die Untersuchungen mit der konfokalen Raman-Spektroskopie zeigten, dass dieseMethode geeignet ist, Diffusionskinetiken im nicht stationären Zustand innerhalb der Membranen zu beobachten. / The knowledge of the microstructure of controlling membranes is very important in order to achieve a defined and constantdrug release from therapeutic systems. Poly(dimethylsiloxane) membranes can be prepared by an addition reaction of linearpoly(dimethylsiloxanes) with terminal vinyl groups and low molecular poly(dimethylsiloxanes) with Si-H functional groups. Forthis reaction a Platinum catalyst is used. By using well characterized starting polymers it is possible to get membranes with astatistically defined microstructure. The network chain length can characterize the microstructure. The distance between twopoints of cross-linking within the network is called network chain length (NCL). The network chain length describes the numberof the dimethyl- siloxane-units between two cross-linking points. The properties of permeation were investigated by using the stadardized permeation coefficient. The permeation coefficient is dependent on the average network chain length of thepoly(dimethylsiloxane) membranes. This relationship was confirmed for 11 benzoic acid and hydroxynaphthalene derivates.Membranes with network chain lengths of 65, 99 and 122 were used for these investigations. The permeation coefficient P*increases slightly with rising network chain length for all 11 model substances. The permeation coefficient of the membraneswith network chain length of 122 was found to be higher by a statistically significant amount than those of membranes with anetwork chain length of 65 - having only 4 exceptions. In order to find other factors which influence the permeation rate, the membrane/water-partition coefficient, the dipole moment and the van der Waals volume were investigated. There was amathematically relationship between the membrane/water-partition coefficient and the permeation coefficient. The volume of themoleculeshad only with membranes with a network chain length of 122 an influence on the permeation. ConfocalRaman-spectroscopy was taken as a pioneering method to investigate the kinetics of diffusion before reaching the steady statein poly(dimethylsiloxane) membranes. Up to now it was only possible to investigate the diffusion process in the steady state. The membrane was always taken as a whole. Raman-spectroscopic measurements do not destroy or change the probe system.Because of the coupled confocal microscope it is possible to measure selectively at a defined point in the membrane. Thereforedynamic processes e.g. can be investigated before reaching the steady state flux. The investigations with confocalRaman-spectroscopy show the possibility to observe diffusion processes in and before the steady state flux with this method.