<p>The sorption/desorption behaviour of n-hexane in high molarmass linear polyethylene (PE) and branched PEs with 0.39 and5.09 hexyl branches per 100 main chain C atoms andcrystallinities between 4 and 82% at 298 K has been studied.Crystal core contents determined by Raman spectroscopy werealways lower than those determined by density measurements. Then-hexane solubilities in the copolymers depended in anon-linear manner on the content of penetrable polymercomponent and were lower for homogeneous copolymers than forheterogeneous copolymers at the same contents of penetrablecomponent. The solubility of hexane in the linear PE sampleswas proportional to the volume fraction of the penetrablepolymer and the solubility was low in comparison with that ofthe branched PE of the same crystallinity. TheCohen-Turnbull-Fujita (CTF) free volume theory was capable ofdescribing the desorption process in the PEs studied. Theconcentration dependence of the thermodynamic diffusivitypredicted by the CTF free volume theory was confirmed by thedata obtained by the differential method, and the differencesbetween the results obtained by the integral and differentialmethods were within the margins of experimental error. Thedependence of the fractional free volume of the penetrablephases on the phase composition suggests that mass transporttakes place from the liquid-like component to the interfacialcomponent and that the penetrant molecules are trapped at theinterfacial sites. The linear PE samples showed a physicallyrealistic trend with a decrease in the geometrical impedancefactor (t) with decreasing degree of crystallinity, whereas theopposite trend was obtained for the copolymers. The decrease int with increasing crystallinity in the copolymers may beexplained by the presence of wide crystal lamellae in the lowcrystallinity samples.</p><p>A novel melt-extrusion method was used to createcircumferential chain orientation in pipes of crosslinked PE.The microstructure of the pipes was characterized usingdifferential scanning calorimetry (DSC), density measurements,X-ray diffraction, infrared dichroism and contractionmeasurements. The mechanical properties were assessed byuniaxial tensile tests. The maximum degree of circumferentialorientation was obtained at the inner wall of the orientedpipe. The oriented pipe material exhibited a 5-15% higherdegree of crystallinity and a greater crystal thickness thanconventionally crosslinked pipe. The circumferential and axialmoduli of the oriented, crosslinked pipe were greater than thecorresponding moduli of the non-oriented crosslinked pipe.</p><p>Blends of single-site materials of linear PE andethyl-branched PE were prepared using solution- and melt-mixingmethods. The thermal properties of the blends were studied byDSC and results obtained by the two mixing methods werecompared. Data obtained for heats of melting andcrystallization, melting and crystallization peak temperaturesand melting and crystallization temperature profiles wereessentially the same for the samples obtained by the two mixingmethods. The heat associated with the high temperature meltingpeak of the blend samples obtained by both preparation methodsafter crystallization at 398 K was higher than that of thelinear polyethylene included in the blends, suggesting that apart of the branched polyethylene crystallized at 398 K.</p><p><b>Key words:</b><i>n</i>-Hexane diffusion, polyethylene, free volume,solubility, sorption, desorption, mechanical properties,orientation, thermal properties, blend.</p>

This study is aimed at understanding the physical and chemical effects that changes in water content have on uranium leaching in sediment containing gravel. It was hypothesized that leaching will be more efficient under unsaturated conditions because flow will be restricted to the smallest pores and will have the most contact with the uranium contaminated sediment. Under saturated conditions, a large portion of the flow will bypass the < 2 mm material, and in turn not come into contact with uranium contaminated material. Batch adsorption and desorption experiments were performed on < 2 mm ERDF sediment to determine the linearity and reversibility of sorption processes and to aid in the interpretation of the leaching experiments. Results of the desorption experiments on aged, contaminated sediments show that the mass percent of sorbed U(VI) released to solution decreased as the sorbed concentration of U(VI) decreased. The opposite trend was observed on freshly contaminated sediments. This indicated that aging increased U(VI) affinity for the solid phase and was attributed to either the crystallization of calcite, which incorporated a portion of the sorbed U(VI) as it crystallized, or the presence of voids in basaltic lithic fragments accessed by diffusion. Column leaching experiments were performed at two water contents on artificially contaminated sediment collected from the Department of Energy’s (DOE) Hanford Site, Washington state. The sediment contained 81.3% gravel (> 2 mm) by mass. Non-reactive tracers were well fit with the convection-dispersion equation (CDE) at both high and low water contents indicating physical equilibrium. The column experimental data were fitted to an analytical solution to the CDE; the results of the modeling show an increase in the distribution coefficient (Kdeffective) with decreasing water content. Several potential explanations for this trend were proposed; one is based on a physical effect in which solute exposure to reactive surfaces changes as a function of water content and the others are based on results of the batch desorption experiments. This work has important implications for the Hanford Site where there is ongoing research regarding the persistence of U(VI) in the vadose zone and underlying aquifer.

In dieser Arbeit wurden einzelne Siliziumdioxid-Partikel (Durchmesser 500nm) in einer elektrodynamischen Vierpolfalle gespeichert und mit Hilfe eines Kohlendioxidlasers aufgeheizt. Die Masse eines gespeicherten Partikels wurde dabei mit hoher Präzision und in situ aus der Auswertung von Streulichtmodulationen gewonnen. Es wurden anhand der zeitlichen Masseänderung laserinduzierte Desorptionen und Adsorptionen von Molekülen beobachtet. Dazu wurde eine weitgehend automatisierte Versuchsanlage aufgebaut. Eine rechnergesteuerte Durchführung der Experimente erfolgte jeweils bis zu einer Dauer mehrerer Tage (Langzeitmessungen). Die Temperatur und die thermische Abstrahlleistung isolierter Partikel wurde mit Hilfe einer modifizierten Planck'schen Strahlungsformel abgeschätzt.

Thesis (Ph.D.)--Drexel University, 2009. / Includes abstract and vita. Includes bibliographical references (leaves 204).

Thesis (M.S.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed Jan. 26, 2010). Includes bibliographical references (p. 40-43).

Thesis (M.S.)--The University of North Carolina at Greensboro, 2008. / Directed by Norman Chiu; submitted to the Dept. of Chemistry and Biochemistry. Title from PDF t.p. (viewed Mar. 19, 2010). Includes bibliographical references (p. 61-64).

The demands on Hydrogen fuel based technologies is ever increasing for substitution or replacing fossil fuel due to superior energy sustainability, national security and reduced greenhouse gas emissions. Currently, the polymer based proton exchange membrane fuel cell (PEMFC), is strongly considered for on-board hydrogen storage vehicles due to low temperature operation, efficiency and low environmental impact. However, the realization of PEMFC vehicles must overcome the portable hydrogen storage barrier. DOE and FreedomCAR technical hydrogen storage targets for the case of solid state hydrides are: (1) volumetric hydrogen density > 0.045 kgH2/L, (2) gravimetric hydrogen density > 6.0 wt%, (3) operating temperature < 150 degrees C, (4) lifetimes of 1000 cycles, and (5) a fast rate of H2 absorption and desorption. To meet these targets, we have focused on lithium borohydride systems; an alkali metal complex hydride with a high theoretical hydrogen capacity of 18 wt.%. It has been shown by Vajo et al. that adding MgH2, improves the cycling capacity of LiBH4. The pressure-composition-isotherms of the destabilized LiBH4 + MgH2 system show an extended plateau pressure around 4-5 bars at 350 degrees C with a good cyclic stability. The mentioned destabilizing mechanism was successfully utilized to synthesize the complex hydride mixture LiBH4 + 1/2MgH2 + Xmol% ZnCl2 catalyst (X=2, 4, 6, 8 and 10) by ball milling process. The added ZnCl2 exhibited some mild catalytic activity which resulted in a decomposition temperature reduction to 270 degrees C. X-ray powder diffraction profiles exhibit LiCl peaks whose intensity increases proportionately with increasing ZnCl2 indicating an interaction between catalyst and hydride system, possibly affecting the total weight percent of desorbed hydrogen. Thermal gravimetric analysis profiles for MgH2 + 5mol% nanoNi and LiBH4 + ZnCl2 + 3mol% nanoNi indicate that small concentrations of nano-nickel acts as an effective catalyst that reduces the mixture desorption temperature to around 225 degrees C and 88 degrees C, respectively. Future work will be focused on thermodynamic equilibrium studies (PCT) on the destabilized complex hydrides.

Asthma, current detection methods and metabolites proposed as asthma markers are described. The limitation of the disease diagnosis is outlined and metabolomics is introduced as the approach carried out within this research with the potential to measure the group metabolites that characterise the metabolic responses of a biological system to a specific disease. Chemistry underlying breathing, current breath collection and analytical techniques are described as well as detection and data processing technology associated within our research. A work-flow for the collection, analysis and processing of exhaled breath samples in respiratory diseases is described. The non-invasive sampling method allows collection of exhaled breath samples on children and adults without experiencing any discomfort. The analysis of exhaled breath samples using thermal desorption gas chromatography mass spectrometry outlines the use of retention index for the alignment of VOCs retention time shifting over time. This methodology enables the creation of a breath matrix for multivariate analysis data processing where each VOC is defined by retention index and most intense fragments of the mass spectrum. This methodology is tested in two cohorts of participants: paediatric asthma and severe asthmatic participants whose breath profiles are compared against healthy controls and within the two asthmatic phenotypes to prospect the markers that differentiate between the different groups. Eight candidate markers are identified to discriminate between asthmatic children and healthy children and seven markers between asthmatics undergoing therapy and healthy controls. The database from severe and paediatric asthma is compared, establishing seven non-age related markers between the two groups. A new interface is developed for the faster analysis of exhaled breath samples using thermal desorption ion mobility mass spectrometry. The interface front end has been modified and optimised to achieve the best sensitivity and resolution of VOCs in exhaled breath. A preliminary study carried out in a small cohort of volunteers shows the feasibility of the technique for the differentiation of asthmatic and healthy adults.

Although silicon (Si) nanostructures exhibit size dependent light emission, which can be attributed to quantum confinement, the role of surface passivation is not yet fully understood. This understanding is central to the development of nanocrystal-based detectors. This study investigated the growth, surface chemistry, passivation with deuterium (D2), ammonia (ND3) and diborane (B2D6) and the resulting optical properties of Si nanostructures. Si nanocrystals less than 6 nm in diameter are grown on SiO2 surfaces in an ultra high vacuum chamber using hot-wire chemical vapor deposition and the as grown surfaces are exposed to atomic deuterium. Temperature programmed desorption (TPD) spectra show that that the nanocrystals surfaces are covered by a mix of monodeuteride, dideuteride and trideuteride species. The manner of filling of the deuteride states on nanocrystals differs from that for extended surfaces as the formation of the dideuteride and trideuteride species is facilitated by the curvature of the nanocrystal. No photoluminescence (PL) is observed from the as grown unpassivated nanocrystals. As the deuterium dose is increased, the PL intensity also begins to increase. This can be associated with increasing amounts of mono-, di- and trideuteride species on the nanocrystal surface, which results in better passivation of the dangling bonds and relaxing of the reconstructed surface. At high deuterium doses, the surface structure breaks down and amorphization of the top layer of the nanocrystal takes place. Amorphization reduces the PL intensity. Finally, as the nanocrystal size is varied, the PL peak shifts, which is characteristic of quantum confinement. The dangling bonds and the reconstructed bonds at the NC surface are also passivated and transformed with D and NDx by using deuterated ammonia (ND3), which is predissociated over a hot tungsten filament prior to adsorption. At low hot wire ND3 doses PL emission is observed at 1000 nm corresponding to reconstructed surface bonds capped by predominantly monodeuteride and Si-ND2 species. As the hot wire ND3 dose is increased, di- and trideuteride species form and intense PL is observed around 800 nm that does not shift with NC size and is associated with defect levels resulting from NDx insertion into the strained Si-Si bonds forming Si2=ND. The PL intensity at 800 nm increases as the ND3 dose is increased and the intensity increase is correlated to increasing concentrations of deuterides. At extremely high ND3 doses PL intensity decreases due to amorphization of the NC surface. In separate experiments, Si NCs were subjected to dissociative (thermal) exposures of ammonia followed by exposures to atomic deuterium. These NCs exhibited size dependent PL and this can be attributed to the prevention of the formation of Si2=ND species. Finally, deuterium-passivated Si NCs are exposed to BDx radicals formed by dissociating deuterated diborane (B2D6) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of low temperature peaks, which can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination. / text

Molecular contaminants on the surface of nanoparticles (NPs) are critical in determining the environmental safety and health (ESH) impacts of NPs. In order to characterize the surface properties that relate to adsorption and desorption interactions, a method has been developed for studying the dynamic interactions of adsorbing species on NP samples. The results are analyzed using a process simulator to determine fundamental properties such as capacity, affinity, rate expressions, and activation energies of NP interactions with contaminants. The method is illustrated using moisture as a representative model compound and particles of SiO₂, HfO₂, and CeO₂, which are three oxides used in semiconductor manufacturing. The effect of particle size and temperature on the surface properties of porous oxide NPs was investigated. Infrared spectra peaks corresponding to the stretching vibration of water molecules were monitored by in-site Fourier transform infrared (FTIR) spectroscopy. These are related to the moisture concentration on the surface of NPs. A transient multilayer model was developed to represent the fundamental steps in the process. The thermal stability of adsorbed species and the strength of bonding to the surface were evaluated by determining the activation energies of the various steps. The results indicate that the surface interaction parameters are dependent on species, temperature, and particle size. SiO₂ has the highest adsorption capacity and therefore is most prone to the adsorption of moisture and similar contaminants. However, the affinity of the NPs for H₂O retention is highest for CeO₂ and lowest for SiO₂. As temperature decreases, NPs exhibit a higher saturated moisture concentration and are more prone to the adsorption of moisture and similar contaminants. Furthermore, smaller NPs have a higher saturated surface concentration and a slower response to purging and desorption. Factors contributing to the environmental and health impact of NPs (extent of surface coverage, capacity, and activation energy of retention) have been investigated during this study. The second objective of this study is to develop a method to measure and control the contamination in ultra-high-purity (UHP) gas delivery systems. Modern semiconductor manufacturing plants have very stringent specifications for the moisture content at the point-of-use, usually below several parts per billion (ppb). When the gas delivery system gets contaminated, a significant amount of purge time is required for recovery of the background system. Therefore, it is critical for high-volume semiconductor manufacturers to reduce purge gas usage as well as purge time during the dry-down process. A method consisting of experimental research and process simulations is used to compare steady-state purge (SSP) process of constant pressure and flow rate with the pressure-cycle purge (PCP) process of cyclic pressure and flow rate at a controlled interval. The results show that the PCP process has significant advantages over the SSP process under certain conditions. It can reduce the purge time and gas usage when the gas purity at point-of-use is the major concern. The process model is validated by data congruent with the experimental results under various operating conditions and is useful in conducting parametric studies and optimizing the purge process for industrial applications. The effect of key operational parameters, such as start time of PCP process as well as choice of PCP patterns has been studied.