Polymers capability to withstand harmful interactions withdifferent environments can be determined by looking at thetransport and mechanical properties of the material exposed tothe medium. The diffusion of a penetrant in a polymer and itsswelling characteristics can be verified by a simplesorption-desorption experiment followed by methodical analysisof the data. Three different systems have been investigated andreported on using the sorption-desorption technique, tensiletesting, compression testing, stress-relaxation and curvefitting routines in Matlab. Fluoropolymers of different repeating unit structure andcrystallinities were exposed to tetrachloroethylene (TCE),water, hydrochloric acid (35%) and hydrobromic acid (47%) at70°C yielding solubility and diffusivity data. Thetransport properties were mostly controlled by the polarity ofthe polymer and to a less degree by the polymer crystallinity.Low solubilities were observed for the aqueous solutes andtheir diffusivities were best fitted using a dual sorption modeassuming no concentration dependent diffusivities. Thepolarisable non-polar TCE showed the highest solubility, andthe diffusivity was solute-concentration dependent. The rate atwhich the surface-concentration approached the saturation levelwas proportional to the product of the Young's modulus, thesquare of the dry polymer thickness and the logarithm of thesolute diffusivity. Data for water-hyperbranched polymer andlimonene-polyethylene confirmed the relationship. Low and high-density poly-ethylene (LDPE, HDPE), crosslinkedethylene vinyltrimetoxy silane (PEX), natural rubber (NR) andacrylonitrile-butadiene rubber were exposed to crude oilcomponents at 25 and 30°C. Solubility data indicated thatthe accessibility of the interfacial components decreased inthe order: cyclohexane, n-hexane/2,2-dimethylbutane andn-decane/n-tetradecane. The free-volume model describeddesorption data better than the semi-empirical exponentialmodel, but the numerical differences were for most practicalapplications negligibly small. The decrease in tensile modulus,yield stress and relaxation modulus for dry HDPE and PEXcompared to n-hexane, n-heptane, cyclohexane andtoluene-swollen samples was clearly caused by thepenetrant-induced plasticisation effect. LDPE and NR-sheets were exposed to limonene at 25°C.The limonene-NR displayed saddle-shape during sorption andcup-shape during desorption were most likely a consequence oflocal differences in limonene concentration that affected thestress state across the sheet thickness. The ratio in bulkmodulus between LDPE and NR was significantly smaller than thecorresponding ratio in tensile modulus and close to the ratioin the degree of anisotropy for the same polymers.Consequently, the bulk modulus is more accurate than thetensile modulus to use when predicting the degree of swellinganisotropy.

<p>Polymers capability to withstand harmful interactions withdifferent environments can be determined by looking at thetransport and mechanical properties of the material exposed tothe medium. The diffusion of a penetrant in a polymer and itsswelling characteristics can be verified by a simplesorption-desorption experiment followed by methodical analysisof the data. Three different systems have been investigated andreported on using the sorption-desorption technique, tensiletesting, compression testing, stress-relaxation and curvefitting routines in Matlab.</p><p>Fluoropolymers of different repeating unit structure andcrystallinities were exposed to tetrachloroethylene (TCE),water, hydrochloric acid (35%) and hydrobromic acid (47%) at70°C yielding solubility and diffusivity data. Thetransport properties were mostly controlled by the polarity ofthe polymer and to a less degree by the polymer crystallinity.Low solubilities were observed for the aqueous solutes andtheir diffusivities were best fitted using a dual sorption modeassuming no concentration dependent diffusivities. Thepolarisable non-polar TCE showed the highest solubility, andthe diffusivity was solute-concentration dependent. The rate atwhich the surface-concentration approached the saturation levelwas proportional to the product of the Young's modulus, thesquare of the dry polymer thickness and the logarithm of thesolute diffusivity. Data for water-hyperbranched polymer andlimonene-polyethylene confirmed the relationship.</p><p>Low and high-density poly-ethylene (LDPE, HDPE), crosslinkedethylene vinyltrimetoxy silane (PEX), natural rubber (NR) andacrylonitrile-butadiene rubber were exposed to crude oilcomponents at 25 and 30°C. Solubility data indicated thatthe accessibility of the interfacial components decreased inthe order: cyclohexane, n-hexane/2,2-dimethylbutane andn-decane/n-tetradecane. The free-volume model describeddesorption data better than the semi-empirical exponentialmodel, but the numerical differences were for most practicalapplications negligibly small. The decrease in tensile modulus,yield stress and relaxation modulus for dry HDPE and PEXcompared to n-hexane, n-heptane, cyclohexane andtoluene-swollen samples was clearly caused by thepenetrant-induced plasticisation effect.</p><p>LDPE and NR-sheets were exposed to limonene at 25°C.The limonene-NR displayed saddle-shape during sorption andcup-shape during desorption were most likely a consequence oflocal differences in limonene concentration that affected thestress state across the sheet thickness. The ratio in bulkmodulus between LDPE and NR was significantly smaller than thecorresponding ratio in tensile modulus and close to the ratioin the degree of anisotropy for the same polymers.Consequently, the bulk modulus is more accurate than thetensile modulus to use when predicting the degree of swellinganisotropy.</p>

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Bibliographische Beschreibung: Weuste, Malte Die Inhibition der Müllerzellschwellung unter hypotonen Bedingungen durch Heparine binding epidermal growth factor-like growth factor (HB-EGF) Universität Leipzig, Dissertation 62 S., 135 Lit., 30 Abb., 2 Tab. Referat: Die Einleitung der Arbeit beschreibt die Müllerzelle als vorherrschende Gliazelle der Säugetiernetzhaut. Müllerzellen eignen sich dadurch als Modell für andere Makrogliazellen des Zentralen Nervensystems. Sie sind an der Regulation des Wasser- und Ionenhaushaltes der Netzhaut beteiligt. Müllerzellen postischämischer sowie mit Bariumionen behandelter Netzhäute schwellen unter hypotonen Bedingungen an. In vielen Versuchen der vorliegenden Arbeit wurde daher ein postischämischer Zustand der Netzhaut durch Zugabe von Bariumionen zu gesunden Netzhäuten simuliert. Die Arbeit untersucht die Rolle des Wachstumsfaktors HB-EGF in der postischämischen Netzhaut der Ratte. Dazu wurde der HB-EGF-Gehalt in postischämischen und in Kontrollnetzhäuten mit Western Blots und immunohistochemischer Färbung dargestellt. Der Einfluss von HB-EGF auf die Müllerzellschwellung wurde an vitalen Müllerzellen in vitro untersucht. Hierzu wurden Müllerzellen in Netzhäuten der Ratte mit einem Vitalfarbstoff angefärbt und über einen Zeitraum von 5 Minuten mit hypotoner extrazellulärer Lösung perfundiert. Die Perfusionslösung diente dabei auch als Träger verschiedener Testsubstanzen. Das Schwellungsverhalten der Müllerzellsomata wurde in diesem Zeitraum mit einem konfokalen laser-scanning Mikroskop aufgezeichnet und mit der zum Mikroskop gehörenden Software ausgewertet. Die Versuche der vorliegenden Arbeit zeigten, dass der HB-EGF-Gehalt der synaptischen Schichten der Netzhaut nach einer Ischämie ansteigt. Es zeigte sich auch, dass HB-EGF eine Müllerzellschwellung im hypotonen Milieu hemmt. Durch Perfusion der Netzhäute mit verschiedenen Rezeptoragonisten und Rezeptorantagonisten sowie Enzyminhibitoren und Ionenkanalblockern konnte das Bild einer möglichen Signalkaskade der Schwellungsinhibition durch HB-EGF gezeichnet werden. An dieser Signalkaskade sind verschiedene Proteinkinasen, ein Anstieg des freien intrazellulären Kalziums, die neuronale Freisetzung von Glutamat, die Aktivierung von glialen Adenosinrezeptoren sowie die Öffnung unterschiedlicher Ionenkanäle beteiligt. Verschiedene Hypothesen zur Ätiologie und Pathogenese der glialen Zellschwellung und zu deren Inhibition werden diskutiert. Abschließend wird die Rolle der glialen Zellschwellung als Teil der Pathogenese von Erkrankungen, die mit einem Hirn- und Netzhautödemen einhergehen, dargestellt. In Zukunft könnten solche Erkrankungen einmal spezifisch mit Substanzen wie dem HB-EGF therapiert werden.

Thesis (PhD)--University of South Australia, 1996

No description available.

Expansive soils are widely found in many parts of the world. Highly active smectite clay mineral Montmorillonite is the major constituent in these clays and can expand or contract up to 15 times of their original volume. Constrained swelling exert large amount of stress causing damage to structures, pavements etc. These clays are also used as barrier materials, Nano-materials in polymer clay Nano composites and drug delivery systems. Several factors influence the swelling potential such as water content, density, voids, electrolyte content and cation exchange capacity. However, molecular scale mechanisms that control swelling behavior in these clays need to be understood. Objectives of this research are to provide an insight into mechanisms that result in swelling of these clays. Molecular modeling is used to build and study solvation of Na-Montmorillonite system. Trajectories of water molecules are captured and the evolutions of interaction energies with swelling are calculated.

The compacted bentonites are used as buffer and backfill materials for engineering barriers for high-level nuclear waste repositories located underground. For this purpose, it is very important to evaluate the swelling characteristics of this clay. The swelling capacity is one of the most important properties of the bentonite clay. The swelling behaviour is due two mechanisms, the crystalline swelling and the osmotic swelling. These mechanisms produce an increase in the distance between the layers of montmorillonite which is one component of bentonite. The result of the swelling capacity is the swelling pressure. It has been studied in several investigations. The results of experimental tests have been collected and compared in this thesis, considering only the Na-dominant bentonite and sand and distilled water as test solution. The experimental tests show that there is only an unique relation between different bentonites in the Na-dominant bentonite and sand mixture swollen depending on its final dry density. Also, the relation between the swelling pressure and the clay void ratio shows the mechanism of the swelling pressure. On the other hand, a mechanistic model is used to predict the swelling pressure of fully saturated bentonite and sand mixture in distilled water. Firstly, it has been compared with the results of experimental tests and it should be pointed out that the model gives good predictions. In addition, the model has been used to make sensitivity analysis with different parameters of bentonite. The most important conclusions in this section show that the swelling pressure mainly depends on the distance among particles. Also, the sensitivity analyses indicate which parameters should be fitted more carefully for future studies to validate this model with different bentonites.

No description available.

No description available.