To see the other types of publications on this topic, follow the link: Capillary and porous materials.
Dissertations / Theses on the topic 'Capillary and porous materials'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Capillary and porous materials.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
López, de Ramos Aura Luisa. "Capillary enhanced diffusion of CO2 in porous media /." Access abstract and link to full text, 1993. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9400131.
Full text
2
Zou, Yuliang. "Modelling of the dynamic effects in capillary pressure in coupling with deformation on the desiccation of porous materials." Thesis, Ecole centrale de Nantes, 2020. http://www.theses.fr/2020ECDN0034.
Full textAbstract:
La durabilité des infrastructures constituées de matériaux poreux, tels que le sol, le sable et les matériaux cimentaires, est étroitement liée aux conditions environnementales. La plupart des mécanismes de détérioration sont régis par l'état d'humidité des matériaux poreux. En effet, l'état d'humidité détermine la répartition de la pression capillaire qui est une force importante pour la déformation solide et pourrait augmenter le risque de fissuration. Cependant, la plupart des modèles d'interaction fluide-solide utilisés pour prédire le transport de l'humidité et de la déformation solide ont ignoré le phénomène physique existant, qui est les effets dynamiques sur la pression capillaire. Cette thèse vise à améliorer le modèle d'interaction fluide solide avec la prise en compte de cet effet de capillarité dynamique. Trois modèles dynamiques correspondant à différents types de matériaux poreux ont été développés. Le premier modèle est disponible pour les matériaux poreux à perméabilité relativement élevée, tels que le sable et le sol. Le deuxième modèle est utilisé pour les matériaux à base de ciments matures à faible perméabilité. Le troisième modèle est développé pour les matériaux cimentaires durcissant exposés à des conditions d’humidité relative extrêmement faibles. Chaque modèle dynamique, et le modèle non dynamique correspondant, ont été utilisés pour simuler des expériences de séchage (drainage) documentées pour le sable, la pâte de ciment mature et le béton durcissant, respectivement. En comparant avec des données expérimentales, les simulations numériques montrent que la modélisation avec effets dynamiques donne de meilleurs résultats que la modélisation non dynamique. Toutes les comparaisons et investigations ont renforcé la nécessité de considérer l'effet de la capillarité dynamique pour prédire le transport d'humidité et la déformation solide pour un séchage rapide (drainage) des matériaux poreux<br>The durability of infrastructure made of porous materials such as soil, sand and cement based materials is closely related to the environmental conditions. Most of the mechanisms of deterioration are governed by moisture state in porous materials. Indeed, the moisture state determines the distribution of capillary pressure which is an important driving force for solid deformation and could increase cracking risk. However, most of fluid-solid interaction models used to predict moisture transport and solid deformation have ignored the existing physical phenomenon dynamic effects on capillary pressure. This thesis aims to refine the fluid-solid interaction model with the consideration of this dynamic capillarity effect. Three dynamic models corresponding to various types of porous materials have been developed. The first model is available for porous materials with relative high permeability such as sand and soil. The second model is used for mature cement-based materials with low permeability. The third model is developed for hardening cement-based materials exposed to extremely low relative humidity condition. Each dynamic model and corresponding non-dynamic model have been implemented to simulate documented drying (drainage) experiments for sand, mature cement paste and hardening concrete, respectively. Compared with experimental data, the numerical simulations show that modeling with dynamic effects gives better results than non dynamic modeling. All comparisons and investigations enhanced the necessity of considering dynamic capillarity effect to predict the moisture transport and solid deformation for fast drying (drainage) of porous materials
3
Maurath, Johannes [Verfasser], and N. [Akademischer Betreuer] Willenbacher. "Tailored Formulation of Capillary Suspensions as Precursor for Porous Sintered Materials / Johannes Maurath ; Betreuer: N. Willenbacher." Karlsruhe : KIT-Bibliothek, 2018. http://d-nb.info/1156327830/34.
Full text
4
Törnkvist, Anna. "Aspects of Porous Graphitic Carbon as Packing Material in Capillary Liquid Chromatography." Doctoral thesis, Uppsala University, Analytical Chemistry, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3306.
Full textAbstract:
<p>In this thesis, porous graphitic carbon (PGC) has been used as packing material in packed capillary liquid chromatography. The unique chromatographic properties of PGC has been studied in some detail and applied to different analytical challenges using both electrospray ionization-mass spectrometry (ESI-MS) and ultra violet (UV) absorbance detection. </p><p>The crucial importance of disengaging the conductive PGC chromatographic separation media from the high voltage mass spectrometric interface has been shown. In the absence of a grounded point between the column and ESI emitter, a current through the column was present, and changed retention behaviors for 3-O-methyl-DOPA and tyrosine were observed. An alteration of the chromatographic properties was also seen when PGC was chemically oxidized with permanganate, possibly due to an oxidation of the few surface groups present on the PGC material. </p><p>The dynamic adsorption of the chiral selector lasalocid onto the PGC support resulted in a useful and stable chiral stationary phase. Extraordinary enantioselectivity was observed for 1-(1-naphthyl)ethylamine, and enantioseparation was also achieved for other amines, amino acids, acids and alcohols. </p><p>Finally, a new strategy for separation of small biologically active compounds in plasma and brain tissue has been developed. With PGC as stationary phase it was possible to utilize a mobile phase of high content of organic modifier, without the addition of ion-pairing agents, and still selectively separate the analytes. </p>
5
Törnkvist, Anna. "Aspects of porous graphitic carbon as packing material in capillary liquid chromatography /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3306.
Full text
6
Neacsu, Valentin. "Modeling and measurement of micro flow in dual scale porous media." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 280 p, 2010. http://proquest.umi.com/pqdweb?did=1998445961&sid=7&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Full text
7
Kharaghani, Abdolreza [Verfasser], and Evangelos [Gutachter] Tsotsas. "Drying and wetting of capillary porous materials : insights from imaging and physics-based modeling / Abdolreza Kharaghani ; Gutachter: Evangelos Tsotsas." Magdeburg : Universitätsbibliothek Otto-von-Guericke-Universität, 2020. http://d-nb.info/1220035491/34.
Full text
8
Xuefeng, Yang. "A network approach to the analysis of mass transfer from a capillary porous medium." reponame:Repositório Institucional da UFSC, 1995. https://repositorio.ufsc.br/xmlui/handle/123456789/157927.
Full textAbstract:
Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnologico<br>Made available in DSpace on 2016-01-08T19:37:50Z (GMT). No. of bitstreams: 1
101465.pdf: 9852443 bytes, checksum: b8cafd1383f95b320b58aaf21d5415f0 (MD5)
Previous issue date: 1995<br>Um modelo de secagem microscópico para o meio poroso capilar é apresentado nesta tese. Este modelo microscópico é baseado em uma abordagem de rede para o meio poroso e é usado para estudar o comportamento da secagem no interior de meio poroso durante o processo de secagem em escala dos poros. A força motora para o transporte do líquido é a força capilar e a transferência de massa na fase gasosa é a difusão de vapor. O efeito Kelvin é considerado neste modelo, ou seja, a interface gás-líquido é tratada como um menisco. A força gravitacional é ignorada pois os tamanhos dos poros e gargantas da rede são relativamente grandes (>20mm). O processo de secagem é simulado usando este modelo em várias redes quadradas 100x20, contendo 2000 poros e 4000 gargantas. O líquido é álcool e o processo de secagem é assumido isotérmico.
9
Thomys, Oliver. "Asymptotic Behaviour of Capillary Problems governed by Disjoining Pressure Potentials." Doctoral thesis, Universitätsbibliothek Leipzig, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:15-20100412-072001-8.
Full text
10
Jacquard, Catherine. "Etude experimentale d'une barriere capillaire avec un modele de laboratoire." Paris, ENMP, 1988. http://www.theses.fr/1988ENMP0097.
Full text
11
Евсина, Наталья Александровна. "Синтез нечеткого регулятора для системы управления процессом сушки капиллярно-пористых материалов". Thesis, НТУ "ХПИ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/19590.
Full textAbstract:
Диссертация на соискание ученой степени кандидата технических наук по специальности 05.13. 03 - системы и процессы управления. - Национальный технический университет "Харьковский политехнический институт", Харьков, 2015.
Диссертация посвящена разработке и совершенствованию метода синтеза нечеткого регулятора, который обеспечивает заданное качество управления сушкой капиллярно-пористых материалов в конвекционной сушилке периодического действия и позволяет создавать системы управления, опирающиеся на экспертные знания. В диссертационной работе усовершенствован метод анализа чувствительности оптимального управления в линейной системе при квадратичном критерии качества, который позволил получить условия нечувствительности этого управления в замкнутой системе к малым изменениям параметров. Показано, что в общем случае необходимо совместное исследование чувствительности оптимизируемого функционала и чувствительности оптимальной траектории движения. Предложенный в работе алгоритм синтеза нечеткого логического регулятора позволяет использовать стандартную форму описания лингвистических переменных и минимальный набор управляющих правил. В работе выполнена оптимизация параметров и структуры нечетких регуляторов, что позволяет с небольшим количеством управляющих правил решать задачу выбора значений коэффициентов регулятора, который минимизирует критерий качества переходного процесса.<br>The thesis on Candidate Degree in Technical Sciences: Specialty 05.13. 03 - management systems and processes.– National Technical University "Kharkov Polytechnic Institute", Kharkov 2015. This thesis is devoted to the development and improvement of the synthesis method of a fuzzy regulator which ensures the specified quality to control the drying of the capillary and porous materials in a convection oven of periodic action and allows creating the control systems basing on the expert knowledge. The work describes the improved method of the optimal control sensitivity analysis in a linear system with a quadratic quality criterion which allowed obtaining the control insensitivity conditions to a slightly changed parameters in a closed system. Basing on the performed analysis the thesis shows the necessity to perform a joint research of the optimized functionality sensitivity and the sensitivity of the optimal movementtrajectory. The thesis offers a simple synthesis algorithm of the fuzzy and logical regulator which provides the ability to use a standard format describing the linguistic variables and a minimum set of the operating rules. The regulators built on the basis of fuzzy logic in some cases are capable to provide higher quality rates of the transition processes in comparison with classic regulators. Using the synthesis methods of fuzzy control algorithms, it is possible to optimize the difficult control loops omitting mathematical model specification.
12
Євсіна, Наталя Олександрівна. "Синтез нечіткого регулятора для системи управління процесом сушіння капілярно-пористих матеріалів". Thesis, НТУ "ХПІ", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/19587.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.13. 03 – системи та процеси управління. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2015.
Дисертацію присвячено розробці та вдосконаленню методу синтезу нечіткого регулятора, який забезпечує задану якість управління сушінням капілярно – пористих матеріалів в конвекційній сушарці періодичної дії та дозволяє створювати системи управління, що спираються на експертні знання. Удосконалено метод аналізу чутливості оптимального управління в лінійній системі при квадратичному критерії якості, який дозволив отримати умови нечутливості цього управління в замкнутій системі до малих змін параметрів. Показано, що в загальному випадку необхідно спільне дослідження чутливості функціонала, що оптимізується і чутливості оптимальної траєкторії руху. Запропоновано алгоритм синтезу нечітко-логічного регулятора, що дозволяє використовувати стандартну форму опису лінгвістичних змінних і мінімальний набір керуючих правил. Здійснено синтез нечітких регуляторів з оптимізацією їх параметрів і структури та запропоновано структурну схему нечіткого контролера. В роботі розроблені імітаційні моделі процесу сушіння КПМ, що описують зміну температури і вологості при природній та комбінованої циркуляції сушильного агенту в камерній сушарці періодичної дії, які використовуються для налаштування адаптивних нечітких регуляторів. Синтезований адаптивний нечіткий регулятор стабілізації температури сушильного агенту дозволяє в широкому діапазоні факторів, що збурюють, отримати мінімальний покращений критерій якості системи управління в порівнянні з класичним регулятором.<br>The thesis on Candidate Degree in Technical Sciences: Specialty 05.13. 03 - management systems and processes.– National Technical University "Kharkov Polytechnic Institute", Kharkov 2015.
This thesis is devoted to the development and improvement of the synthesis method of a fuzzy regulator which ensures the specified quality to control the drying of the capillary and porous materials in a convection oven of periodic action and allows creating the control systems basing on the expert knowledge. The work describes the improved method of the optimal control sensitivity analysis in a linear system with a quadratic quality criterion which allowed obtaining the control insensitivity conditions to a slightly changed parameters in a closed system. Basing on the performed analysis the thesis shows the necessity to perform a joint research of the optimized functionality sensitivity and the sensitivity of the optimal movementtrajectory. The thesis offers a simple synthesis algorithm of the fuzzy and logical regulator which provides the ability to use a standard format describing the linguistic variables and a minimum set of the operating rules. The regulators built on the basis of fuzzy logic in some cases are capable to provide higher quality rates of the transition processes in comparison with classic regulators. Using the synthesis methods of fuzzy control algorithms, it is possible to optimize the difficult control loops omitting mathematical model specification.
13
Stol, Remco. "Capillary electrochromatography with porous particles." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2002. http://dare.uva.nl/document/61674.
Full text
14
Bandini, Simone <1976>. "La risalita capillare nei materiali da costruzione porosi e processi elettrocinetici." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1780/.
Full text
15
Alvarellos, Jose. "Fundamental Studies of Capillary Forces in Porous Media." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5314.
Full textAbstract:
The contact angle defined by Young's equation depends on the ratio between solid and liquid surface energies. Young's contact angle is constant for a given system, and cannot explain the stability of fluid droplets in capillary tubes. Within this framework, large variations in contact angle and explained aassuming surface roughness, heterogeneity or contamination. This research explores the static and dynamic behavior of fluid droplets within capillary tubes and the variations in contact angle among interacting menisci. Various cases are considered including wetting and non-wetting gluids, droplets in inclined capillary tubes or subjected to a pressure difference, within one-dimensional and three-dimensional capillary systems, and under static or dynamic conditions (either harmonic fluid pressure or tube oscillation). The research approach is based on complementary analytical modeling (total energy formulation) and experimental techniques (microscopic observations). The evolution of meniscus curvatures and droplet displacements are studied in all cases. Analytical and experimental results show that droplets can be stable within capillary tubes even under the influence of an external force, the resulting contact angles are not constant, and bariations from Young's contact angle aare extensively justified as menisci interaction. Menisci introduce stiffness, therefore two immiscible Newtonian fluids behave as a Maxwellian fluid, and droplets can exhibit resonance or relaxation spectral features.
16
Joncourt, Laurent. "Réactivité des matériaux carbones vis-à-vis du sodium." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0200.
Full textAbstract:
La fixation du sodium a été étudiée dans différents matériaux carbonés, principalement trois cokes de brai graphitisables et sept anthracites de provenances différentes. Ces matériaux constituent en effet les revêtements cathodiques des cuves d’électrolyse servant à la production de l’aluminium et on pense que la pénétration (insertion) du sodium dans ces matériaux carbonés est responsable de leur dégradation. Nous nous sommes tout d’abord attachés à décrire l’évolution de ces matériaux au cours du traitement thermique. Les anthracites sont des matériaux hétérogènes, poreux et polyphasés qui évoluent brutalement entre 2000°C et 2400°C suivant leur provenance pour devenir des carbones graphitisables ou du moins partiellement graphitisables. Trois modes de fixation de sodium ont été observés : insertion, adsorption et condensation capillaire. Pour tous ces carbones non graphitisés, le paramètre déterminant pour l’insertion est la température de traitement thermique : plus celle-ci est élevée, plus la quantité de sodium inséré est faible. Enfin plus le matériau est poreux plus les phénomènes de sorption sont importants<br>This work is related to the interaction of sodium with carbon materials in particular with three graphitizable pitch coke and seven different anthracites. Indeed, these carbons are widely used as cathodic materials in the aluminum electrolysis cells, and there is a general agreement that the penetration of sodium atoms is responsible of the swelling and subsequent destruction of the electrode. At first, we tried to describe the evolution of the microtexture of these materials during heat treatment. Our results (X ray diffraction, Raman spectroscopy and pycnometry) show that the anthracites are highly porous, heterogeneous compounds. They are found to evolue at about 2000-2400°C to become partially graphitizable carbons. Concerning the interaction of sodium with these materials, three phenomena are observed : intercalation, adsorption and capillary condensation. The sodium intercalation is found to be very sensitive to the previous heat treatment temperature : the uptake of intercalated sodium is all the more important the heat treatment temperature is lower. The non-intercalated sodium uptake is correlated to the porous texture of these materials
17
Zhang, Jin. "Shakedown of porous materials." Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1I044/document.
Full textAbstract:
Cette thèse est consacrée à la détermination des états limites de l'adaptation des matériaux ductiles poreux sur la base du théorème de Melan et en considérant le modèle de la sphère creuse. Dans un premier temps, nous proposons le critère analytique macroscopique d'adaptation avec la matrice de von Mises sous deux charges particuliers, alterné et pulsé. Le critère analytique dépend des première et seconde invariants des contraintes macroscopiques, du signe du troisième et du coefficient de Poisson. Ensuite, ce critère est étendu aux charges cycliques répétées générales par la construction d'un champ de contraintes résiduelles d'essai plus approprié permettant simultanément des calculs analytiques et l'amélioration du modèle précédent. De plus, il est également utilisé pour les matériaux ductiles poreux avec une matrice de Drucker-Prager.L'idée repose d'abord sur la solution exacte pour le charge purement hydrostatique. Il s'avère que la ruine se produit par fatigue. Ensuite, des champs de contrainte d'essai appropriés sont construits avec des termes supplémentaires pour capter les effets de cisaillement. Le domaine de sécurité, défini par l'intersection du domaine d'adaptationet celui d'analyse limite (la ruine survenant brusquement par formation d'un mécanisme au premier cycle), est entièrement comparé avec des simulations élasto-plastique incrémentales et des calculs directs simplifiés.Enfin, nous fournissons une méthode numérique directe pour prédire le domaine de sécurité de l'adaptation des matériaux poreux soumis à des charges variant de manière indépendante en considérant le chemin critique du domaine de chargement au lieu de l'histoire entière. Le problème de l'adaptation est transformé en un problème d'optimisation de grande taille, qui peut être résolu efficacement par l'optimiseur non-linéaire IPOPT pour donner non seulement le facteur de charge limite, mais aussi le champ de contrainte résiduelle correspondant à l'état d'adaptation<br>This thesis is devoted to the determination of shakedown limit states of porous ductile materials based on Melan's static theorem by considering the hollow sphere model, analytically and numerically. First of all, we determine the analytical macroscopic shakedown criterion of the considered unit cell with von Mises matrix under alternating and pulsating special loading cases. The proposed macroscopic analytical criterion depends on the first and second macroscopic stresses invariants, the sign of the third one and Poisson's ratio. Then, the procedure is extended to the general cyclically repeated loads by the construction of a more appropriate trial residual stress field allowing analytical computations and the improvement of the previous model simultaneously. Moreover, this approach is applied to porous materials with dilatant Drucker-Prager matrix.The idea relies firstly on the exact solution for the pure hydrostatic loading condition. It turns out that the collapse occurs by fatigue. Next, suitable trial stress fields are built with additional terms to capture the shear effects. The safety domain, defined by the intersection of the shakedown limit domain and the limit analysis domain corresponding to the sudden collapse by development of a mechanism at the first cycle, is fully compared with step-by-step incremental elastic-plastic simulations and simplified direct computations. At last, we provide a direct numerical method to predict the shakedown safety domain of porous materials subjected to multi-varying independent loadings by considering the critical loading path of the load domain instead of the whole history. The shakedown problem is transformed into a large-size optimization problem, which can be solved efficiently by the non-linear optimizer IPOPT to give out not only the limit load factor, but also the corresponding residual stress field for the shakedown state
18
Gong, Xuehui. "POROUS POLYMERIC FUNCTIONAL MATERIALS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1595256175834586.
Full text
19
Palakurthi, Nikhil Kumar. "Direct Numerical Simulation of Liquid Transport Through Fibrous Porous Media." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406881191.
Full text
20
Jiang, Tong. "Porous tin(IV) sulfide materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0007/NQ41557.pdf.
Full text
21
Tchang, Cervin Nicholas. "Porous Materials from Cellulose Nanofibrils." Doctoral thesis, KTH, Fiberteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155065.
Full textAbstract:
In the first part of this work a novel type of low-density, sponge-like material for the separation of mixtures of oil and water has been prepared by vapour deposition of hydrophobic tri-chloro-silanes on ultra-porous cellulose nanofibril (CNF) aerogels. To achieve this, a highly porous (>99%) robust CNF aerogel with high structural flexibility is first formed by freeze-drying an aqueous suspension of the CNFs. The density, pore size distribution and wetting properties of the aerogel can be tuned by selecting the concentration of the CNF suspension before freeze-drying. The hydrophobic light-weight aerogels are almost instantly filled with the oil phase when they selectively absorb oil from water, with a capacity to absorb up to 45 times their own weight. The oil can subsequently be drained from the aerogel and the aerogel can then be subjected to a second absorption cycle. The second part is about aerogels with different pore structures and manufactured with freeze-drying and supercritical carbon dioxide for the preparation of super slippery surfaces. Tunable super slippery liquid-infused porous surfaces (SLIPS) were fabricated through fluorination of CNFsand subsequent infusion with perfluorinated liquid lubricants. CNF-based self-standing membranes repelled water and hexadecane with roll-off angles of only a few degrees. The lifetime of the slippery surface was controlled by the rate of evaporation of the lubricant, where the low roll-off angle could be regained with additional infusion. Moreover, adjusting the porosity of the membranes allowed the amount of infused lubricant to be tuned and thereby the lifetime. The CNF-based process permitted the expansion of the concept to coatings on glass, steel, paper and silicon. The lubricant-infused films and coatings are optically transparent and also feature self-cleaning and self-repairing abilities. The third part describes how porous structures from CNFs can be prepared in a new way by using a Pickering foam technique to create CNF-stabilized foams. This technique is promising for up-scaling to enable these porous nanostructured cellulose materials to be produced on a large scale. With this technique, a novel, lightweight and strong porous cellulose material has been prepared by drying aqueous foams stabilized with surface-modified CNFs. Confocal microscopy and high-speed video imaging show that the long-term stability of the wet foams can be attributed to the octylamine-coated, rod-shaped CNF nanoparticles residing at the air-liquid interface which prevent the air bubbles from collapsing or coalescing. Careful removal of the water yields a porous cellulose-based material with a porosity of 98 %, and measurements with an autoporosimeter (APVD) reveal that most pores have a radius in the range of 300 to 500 μm. In the fourth part, the aim was to clarify the mechanisms behind the stabilizing action of CNFs in wet-stable cellulose foams. Factors that have been investigated are the importance of the surface energy of the stabilizing CNF particles, their aspect ratio and charge density, and the concentration of CNF particles at the air-water interface. In order to investigate these parameters, the viscoelastic properties of the interface have been evaluated using the pendant drop method. The properties of the interface have also been compared by foam stability tests to clarify how the interface properties can be related to the foam stability over time. The most important results and conclusions are that CNFs can be used as stabilizing particles for aqueous foams already at a concentration as low as 5 g/L. The reasons for this are the high aspect ratio which is important for gel formation and the viscoelastic modulus of the air-water interface. Foams stabilized with CNFs are therefore much more stable than foams stabilized by cellulose nanocrystals (CNC). The charge density of the CNFs affects the level of liberation of the CNFs within large CNF aggregates and hence the number of contact points at the interface, and also the gel formation and viscoelastic modulus. The charges also lead to a disjoining pressure related to the long-range repulsive electrostatic interaction between the stabilized bubbles, and this contributes to foam stability. In the fifth part, the aim was to develop the drying procedure in order to producea dry porous CNF material using the wet foam as a precursor and to evaluate the dry foam properties. The wet foam was dried in an oven while placed on a liquid-filled porous ceramic frit to preserve and enhance the porous structure in the dried material and prevent the formation of larger cavities and disruptions. The cell structure has been studied by SEM microscopy and APVD (automatic pore volume distribution). The mechanical properties have been studied by a tensile tester (Instron 5566) and the liquid absorption ability with the aid of the APVD-equipment. By changing the charge density of the CNFs it is possible to prepare dry foams with different densities and the lowest density was found to be 6 kg m-3with a porosity of 99.6 %. The Young ́s modulus in compression was 50 MPa and the energy absorption was 2340kJ m-3 for foams with a density of 200 kg m-3. The liquid absorption of the foam with a density of 13 kg m-3 is 34 times its own weight. By chemically cross-linking the foam,it wasalso possible to empty the liquid-filled foams by compression and then to reabsorb the liquid to the same degree with maintained foam integrity. This new processing method also shows great promise for preparing low-density cellulose foams continuously and could be very suitable for industrial up-scaling.<br><p>QC 20141103</p>
22
Parrouffe, Jean-Michel. "Combined convective and infrared drying of a capillary porous body." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39371.
Full textAbstract:
This research has resulted in the design and development of an experimental facility to study the combined convective infrared (I.R.) drying process of a capillary porous material (glass beads) in high temperature flow conditions.<br>The necessity to decrease the heat transfer coefficient for the effect of high mass transfer flux (when convection is combined with I.R. heating) has been demonstrated. Further, the analogy between the transfer of heat and mass expressed in terms of average heat and mass transfer coefficient ratios has been verified to apply when the surface is not contaminated. Experiments have also showed that there is a link between the evaporation temperature and crust formation at the evaporating surface. Moreover, an increase in the heat transfer coefficient was observed when the surface reaches the boiling point and is higher than that of the flowing air. Lastly, it was observed that the critical moisture content is independent of the convective drying parameters, sample thickness and the overall incident heat flux.<br>A drying front model is also presented and tested with the experimental results in convection drying and for the combined process. The drying time, the bottom temperature evolution, the surface temperature evolution up to the critical point and the overall shape of the drying rate curve were well reproduced by the model. Simulations have also showed that the effect of the diffusion mass flux on the heat and mass transfer coefficients leads to a decrease of the evaporation rate by a maximum of 8% for both the purely convective and combined processes.
23
Nourdeen, Hasan. "Upscaling immiscible capillary-controlled two-phase flow in porous media." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/61482.
Full textAbstract:
This thesis focuses primary on two-phase displacements under capillary-controlled flow conditions at relatively large scales, considering solution techniques that capture the dynamics of two-phase displacements for homogeneous flow domains, and deriving representative averages for heterogeneous systems with strong spacial variations in two-phase properties. First, we review main flow mechanisms encountered at large scales when capillary forces dominate the displacement process, where we present main solution techniques for homogeneous flow domains and introduce analytical treatments for other flow mechanisms that do not follow standard time-scaling. We also present a comprehensive investigation of spontaneous imbibition processes in porous rocks both numerically and analytically, and propose a simplified but accurate analytic approximation using perturbation theory, that considerably improves the implementation process, as compared with the original analytical solution. After that, an investigation of the impact of capillary backpressure on counter-current flow is performed, as this is considered one of the main drawbacks in using the continuum modelling approach. We then apply steady-state capillary-controlled upscaling in heterogeneous environment, where large-scale invasion percolation is coupled with a conventional Darcy solver to identify large-scale trapping due to capillary forces. In other words, a phase may fail to form a connected path across a given domain at capillary equilibrium, and some regions therefore may produce disconnected clusters. In such cases, conventional upscaling processes might not be accurate since identification and removal of these isolated clusters are extremely important to the global connectivity of the system and the stability of the numerical solvers. We present a comprehensive investigation using random absolute permeability fields, for water-wet, oil-wet and mixed-wet systems, where we show that in oil-wet and mixed-wet media, large-scale trapping of oil controlled by variations in local capillary pressure, may be more significant than the local trapping controlled by pore-scale displacement.
24
Aker, Eyvind. "A Numerical Study of Capillary and Viscous Drainage in Porous Media." Doctoral thesis, Norwegian University of Science and Technology, Department of Physics, 1999. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1975.
Full textAbstract:
<p>This work concentrates on the flow properties when one fluid displaces another fluid in a network of pores and throats. We consider the scale where individual pores enter the description and we use a network model to simulate the displacement process. The network model, representing the pores and the throats in the porous media, consists of a square lattice of cylindrical tubes.</p><p>Network models together with experimental work on real porous systems, have been successful in describing important properties of the fluid-fluid displacement. In this thesis we study the interplay between the pressure build up in the fluids and the displacement structure during drainage. Drainage is when a nonwetting fluid displaces a wetting fluid in porous media.</p><p>We have found that our network model properly describes the burst dynamics and the pressure buildup due to capillary and viscous forces in the displacements. With respect to the local capillary pressures of menisci in the network, we model the tubes as if they were hourglass shaped. This has shown to make the model closer to the dynamics of real displacements in porous media. There is also good correspondence between the simulated temporal evolution of the fluid pressures and earlier results from experiments and simulations in slow drainage. </p><p>We have used the network model to study the stabilization mechanisms when a stable front develops. We consider two-dimensional horizontal displacements where the viscous forces stabilize the front and gravity might be neglected. In particular, we have calculated the pressure difference between the fluids, that is the capillary pressure, along the invasion front. We find that the capillary pressure between two points along the front varies almost linearly as function of height separation in the directions of the displacement, This is quite surprising since the viscous force field is expected to be inhomogeneous due to trapping of wetting fluid and to the fractal displacement structure.</p><p>We present an alternative view on the displacement process based on the observation that nonwetting fluid flows in separate strands (paths) along the front were wetting fluid is displaced. We show that the strands are loopless because wetting fluid may be trapped in single tubes surrounded by nonwetting fluids. By using the alternative view we, present arguments about the pressure behaviour in the front. The arguments are supported by numerical results, and we also show that they might influence the scaling relation between the front width and the injection rate. As a consequence of our findings, we conclude that earlier suggested theories which do not include the effect of nonwetting fluid flowing in strands, are nor compatible with drainage when strands dominate the displacement process. </p>
25
VELASQUEZ, MAO ILICH ROMERO. "FLOW OF EMULSIONS IN POROUS MEDIA: EXPERIMENTS AND CAPILLARY NETWORK MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15337@1.
Full textAbstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>Objetivo: Transporte de emulsões num meio poroso é relevante para diversas
aplicações em sub-superfície. Muitos processos de recuperação melhorada
de petróleo envolvem formação de emulsões. A modelagem do
fluxo de emulsões num meio poroso é extremamente desafiante. As descrições disponíveis baseadas na viscosidade efetiva não são validas quando
o tamanho das gotas é da mesma ordem de magnitude que o tamanho dos
corpos de poros num meio poroso. Neste caso, intercepção e captura de
gotas podem bloquear parcialmente a passagem dos poros e um modelo
apropriado deve ser capaz de descrever estas mudanças locais de mobilidade.
O modelo desenvolvido neste trabalho é baseado na relação vazão e
queda de pressão do escoamento de emulsões através de capilares com constri
ção. Um modelo de redes de capilares é construído com objetivo de obter
parâmetros macroscópicos a partir do comportamento microscópico. Os resultados
mostram a variação da permeabilidade com o número de capilaridade
e propriedades da emulsão. Para baixas vazões, ou baixos números de
capilaridade, as gotas maiores bloqueiam parcialmente os poros pequenos,
resultando em uma redução da permeabilidade. Para altas vazões, o gradiente
de pressão em cada capilar é alto o suficiente para forçar as gotas
fluir através da constrição. Consequentemente, a permeabilidade aumenta
com o número de capilaridade. Um programa, escrito na linguagem Fortran,
é desenvolvido neste trabalho para simular o escoamento monofásico e
bifásico de emulsões através de um meio poroso utilizando o modelo de rede
de capilares. Na modelagem monofásica, os resultados apresentam uma boa
concordância com as medidas experimentais feitas em mostras de arenito.
Na modelagem bifásica, a comparação dos resultados entre a injeção da fase
continua da emulsão e a injeção de emulsões (fase continua mais gotas) sobre
uma rede inicialmente saturada com óleo mostra um aumento no fator
de recuperação de óleo e uma frente de deslocamento mais uniforme no caso
de injeçãode emulsão.<br>Objective: Transport of emulsions in porous media is relevant to several
subsurface applications. Many enhanced oil recovery processes involve emulsion
formation and their flow in some form. Modeling the flow of emulsion
in porous media is extremely challenging. The available descriptions based
on effective viscosity are not valid when the drop size is of the same order of
magnitude as the pore-throat size. In this case, drop straining and capturing
may partially block the pore passage and an accurate model should be able
to describe this local changes on mobility. The model developed in this work
is based on the flow rate-pressure drop relationship of emulsion flow through
constricted capillaries. A capillary network model is constructed in order to
obtain macroscopic parameters from upscaling of the microscopic behavior.
The results show how the permeability changes with Darcy velocity and
emulsion properties. At low flow rates, the large drops partially block the
smallest pores, leading to a low permeability. At high flow rates, the pressure
gradient in each capillary is strong enough to force the drops to flow
through the constrictions. Consequently, the permeability rises with capillary
number. A program, written in Fortram language, based on network
model is developed in this work to simulate the single phase and two phase
flow of emulsion through a porous medium. In the single phase model, the
results show good agreement with experimental measurements on samples
of sandstone. In the two phase model, the comparison of results between the
injection of the continuous phase of emulsion and the injection of emulsions
(with drops) on a network initially saturated with oil shows an increase in
the oil recovery factor and a more uniform displacement front in the case
of emulsion injection.
26
NOGUEIRA, GIOVANE BARROSO LIMA. "ANALYSIS OF EMULSION FLOW THROUGH POROUS MEDIA USING CAPILLARY NETWORK MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=18104@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>Emulsões podem ser utilizadas como agentes de controle de mobilidade em
diferentes processos de recuperação melhorada de petróleo e armazenamento de
carbono em reservatórios porosos. A aplicação desta técnica, com a escolha
correta das características das emulsões injetadas e a determinação das condições
de operação ótimas, requer um entendimento adequado do escoamento de
emulsões em meios porosos. As características macroscópicas do fluxo de
emulsões através de meios porosos estão diretamente ligadas ao escoamento
bifásico na escala de poros. Modelos de rede de capilares permitem a
implementação dos mecanismos de fluxo das gotas nas gargantas de poros e
fornecem parâmetros macroscópicos do escoamento. Neste trabalho, o
escoamento de emulsões em meios porosos é analisado através de um modelo
dinâmico de rede de capilares tridimensional e não-estruturada. A distribuição de
pressão nos poros, e consequentemente o fluxo em cada capilar da rede, é
determinada pelo balanço de massa em cada poro. O efeito das gotas da fase
dispersa no comportamento do escoamento em cada elemento da rede é descrito
por um fator de bloqueio de fluxo baseado em resultados experimentais de
escoamento de emulsões através de micro capilares com gargantas. O fator de
bloqueio descreve a mudança da condutividade de cada elemento e é uma função
da geometria da garganta, do tamanho e concentração volumétrica da fase
dispersa e do número de capilaridade local. A distribuição de concentração da
fase dispersa ao longo da rede é descrita através de uma equação de transporte de
massa, permitindo assim o estudo do processo de filtragem de gotas nos poros e o
estudo da injeção alternada de água e emulsão. A integração no tempo do modelo
dinâmico é feita por um método semi-implícito e o sistema de equações não linear
obtido a cada passo de tempo é resolvido através de um método iterativo. Os
resultados apresentam a evolução da redução da permeabilidade e concentração de
gotas na saída do meio poroso em função do tamanho das gotas, da vazão de
injeção, da concentração da emulsão injetada e do volume injetado de emulsão. A
análise da injeção alternada de água-emulsão mostra claramente o bloqueio de
poros por gotas da emulsão e a alteração no padrão de escoamento após reiniciada
a injeção de água.<br>Emulsions can be used as mobility control agents in different enhanced oil
recovery and carbon storage methods in oil reservoirs. The application of this
technique, with the correct choice of the injected emulsion characteristics and the
determination of optimal operating conditions, requires an adequate understanding
of the emulsion flow in porous media. The macroscopic characteristics of the
emulsion flow through porous media are directly linked to the two-phase flow at
the pore scale. Capillary network models allow the implementation of the drop
flow mechanisms in the pore throats and the determination of macroscopic flow
parameters. In this work, emulsion flow in porous media is analyzed through an
unstructured 3D dynamic network model. The pressure distribution, and
consequently the flow rate in each capillary of the network, isdetermined by mass
balance equation in each pore. The effects of the drops of dispersed phase in the
flow behavior within each element of the network is described by a flow blocking
factor based on experimental results on emulsion flow through single
microcapillary tubes with throats. The blocking factor describes the changes in the
conductivity of each element and it is a function of the throat geometry, the size
and volumetric concentration of the dispersed phase and the local capillary
number. The concentration distribution of the dispersed phase along the network
is described by a mass transport equation, allowing the study of the filtration
process of the drops in the pores and the analysis of the alternate injection of
water and emulsion.Time integration in the dynamic model is performed by a
semi-implicit method and the non-linear system of equations obtained in each
time step is solved by an iterative method. The results illustrate the evolution of
the permeability reduction and the effluent concentration of drops as a function of
the drops size, injection flow rate, concentration of the injected emulsion and
injected volume of emulsion. The analysis of the emulsion/water alternate
injection clearly shows the pore blockage by the emulsion drops and the change in
the flow pattern after the reinjection of water.
27
BARTOLOMEU, LUCAS SALES PEREIRA. "CAPILLARY NETWORK MODEL OF POLYMERIC SOLUTION FLOW IN A POROUS MEDIA." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=30921@1.
Full textAbstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>A injeção de soluções poliméricas tem sido utilizada em muitas aplicações para aumentar a viscosidade da fase aquosa e, por conseguinte, reduzir a elevada razão de mobilidade durante o deslocamento de óleo num meio poroso. Evidências experimentais mostraram também que o comportamento viscoelástico de algumas soluções poliméricas pode contribuir para um melhor deslocamento do óleo na escala de poros, reduzindo assim, a saturação de óleo residual. Este comportamento na escala de poros não é claramente compreendido já que a modelagem de um fluxo viscoelástico de uma solução polimérica em meios porosos é extremamente desafiadora. O comportamento do escoamento em escala macroscópica está diretamente associado com o fluxo extensional dominante através das gargantas e poros que formam o meio poroso. Muitos modelos têm sido desenvolvidos com o objetivo de descrever o efeito extensional observados no fluxo de soluções poliméricas de elevado peso molecular. O modelo desenvolvido neste trabalho baseia-se na relação entre a vazão e a queda de pressão do escoamento de soluções poliméricas através de capilares com garganta que servem como um modelo simples da geometria das gargantas de poro. Um modelo de rede de capilares bidimensional foi desenvolvido para obter os parâmetros macroscópicos do escoamento a partir do entendimento do comportamento microscópico. No modelo monofásico, os resultados apresentam efeitos de diferentes parâmetros reológicos no comportamento macroscópico do escoamento. Para estudar o escoamento bifásico, um modelo de rede dinâmico foi desenvolvido. Os resultados obtidos fornecem uma descrição mais detalhada do processo de deslocamento de óleo pela fase aquosa.<br>Injection of a polymer solution is used in many applications to increase the viscosity of the water phase and therefore reduce the high mobility ratio during oil displacement in porous media. Experimental evidence has shown that the viscoelastic behavior of some polymer solutions may contribute to a better oil displacement at the pore-level, reducing the residual oil saturation. This pore-level behavior is not clearly understood. Modeling viscoelastic flow of polymeric solutions in porous media is extremely challenging. The macroscopic flow behavior is directly associated with the extensional dominant flow through pore throats that form the porous media. Accurate models should be able to describe the extensional thickening effect observed in the flow of dilute high molecular weight polymer solutions. The model developed in this work is based on the flow rate-pressure drop relationship of polymer solution flow through constricted capillaries that serves as a simple model of the geometry of pore throats. A two-dimensional capillary network model is constructed in order to obtain macroscopic parameters from upscaling of the microscopic behavior. In single-phase flow, results show the effect of different rheological parameters on the macroscopic flow behavior. To study a two-phase flow, a dynamic network model was developed. The results obtained
provide a more detailed description of the oil displacement by the water phase.
28
Alsayednoor, Jafar. "Modelling and characterisation of porous materials." Thesis, University of Glasgow, 2013. http://theses.gla.ac.uk/4808/.
Full textAbstract:
Porous materials possessing random microstructures exist in both organic (e.g. polymer foam, bone) and in-organic (e.g. silica aerogels) forms. Foams and aerogels are two such materials with numerous engineering and scientific applications such as light-weight cores in sandwich structures, packaging, impact and crash structures, filters, catalysts and thermal and electrical insulators. As such, design and manufacture using these materials is an important task that can benefit significantly from the use of computer aided engineering tools. With the increase in computational power, multi-scale modelling is fast becoming a powerful and increasingly relevant computational technique. Ultimately, the aim is to employ this technique to decrease the time and cost of experimental mechanical characterisation and also to optimise material microstructures. Both these goals can be achieved through the use of multi-scale modelling to predict the macro-mechanical behaviour of porous materials from their microstructural morphologies, and the constituent materials from which they are made. The aim of this work is to create novel software capable of generating realistic randomly micro-structured material models, for convenient import into commercial finite element software. An important aspect is computational efficiency and all techniques are developed paying close attention to the computation time required by the final finite element simulations. Existing methods are reviewed and where required, new techniques are devised. The research extensively employs the concept of the Representative Volume Element (RVE), and a Periodic Boundary Condition (PBC) is used in conjunction with the RVEs to obtain a volume-averaged mechanical response of the bulk material from the micro-scale. Numerical methods such as Voronoi, Voronoi-Laguerre and Diffusion Limited Cluster-Cluster Aggregation are all employed in generating the microstructures, and where necessary, enhanced in order to create a wide variety of realistic microstructural morphologies, including mono-disperse, polydisperse and isotropic microstructures (relevant to gas-expanded foam materials) as well as diffusion-based microstructures (relevant for aerogels). Methods of performing large strain simulations of foams microstructures, up to and beyond the onset strain of densification are developed and the dependence of mechanical response on the size of an RVE is considered. Both mechanical and morphological analysis of the RVEs is performed in order to investigate the relationship between mechanical response and internal microstructural morphology of the RVE. The majority of the investigation is limited to 2-d models though the work culminates in extending the methods to consider 3-d microstructures.
29
Jacobs, Tia. "Self-assembly of new porous materials." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/3970.
Full textAbstract:
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009.<br>ENGLISH ABSTRACT: The primary objective of the work was to prepare and investigate new porous
materials using the principles of crystal engineering. Both organic and metal-organic
systems were studied and the work can best be divided into two separate sections:
1. The crystal engineering of Dianin’s Compound, a well-known organic host.
2. The design and synthesis of a series of related porous coordination compounds
consisting of discrete, dinuclear metallocycles.
The first section discusses the synthetic modification of Dianin’s compound in order
to engineer a new clathrate host with an altered aperture size. Although this study
ultimately failed to isolate the host material in its porous guest-free form, the work led
to the discovery of a chiral host framework that aligns guest molecules in a polar
fashion, and consequently displays non-linear optical properties. These findings are
unprecedented in the long history of crystal engineering of Dianin’s compound and its
analogues. This section also describes desorption studies of the new inclusion
compound, as well as the known thiol analogue of Dianin’s compound. Systematic
characterisation of these desorbed phases has raised interesting fundamental questions
about desolvation processes in general.
The second section constitutes the major portion of the work. A series of related
isostructural coordination metallocycles were synthesised and their structure-property
relationships were investigated using a variety of complementary techniques. These
metallocyclic compounds all crystallise as solvates in their as-synthesised forms, and
different results are obtained upon desolvation of the materials. In each case,
desolvation occurs as a single-crystal to single-crystal transformation and three new
“seemingly nonporous” porous materials were obtained. A single-crystal diffraction
study under various pressures of acetylene and carbon dioxide was conducted for one
of the porous metallocycles. This enabled the systematic study of the host
deformation with increasing equilibrium pressure (i.e. with increasing guest
occupancy). The observed differences in the sorption behaviour for acetylene and
carbon dioxide are discussed and rationalised. Gravimetric gas sorption isotherms were also recorded for the three different porous materials and the diffusion of bulkier
molecules through the host was also investigated structurally. Finally, a possible gas
transport mechanism is postulated for this type of porous material (i.e. seemingly
nonporous), and this is supported by thermodynamic and kinetic studies, as well as
molecular mechanics and statistical mechanics simulations.<br>AFRIKAANSE OPSOMMING: Die primêre doel van die werk was om nuwe poreuse materiale te berei en deur die
toepassing van beginsels van kristalmanipulasie (E. crystal engineering) te ondersoek.
Beide organiese- en metaal-organiese sisteme is bestudeer en die werk kan in twee
kategorieë verdeel word:
1. Die kristalmanipulasie van Dianin se verbinding, ’n bekende organiese
gasheer.
2. Die ontwerp en sintese van ’n reeks verwante poreuse koördinasieverbindings
wat uit diskrete, binukleêre metallosiklieseverbindings bestaan.
Die eerste deel handel oor die sintetiese verandering van Dianin se verbinding om ’n
nuwe klatraatgasheer met ’n veranderde spleetgrootte te vorm. Alhoewel hierdie
studie nie daarin geslaag het om die gasheer in sy poreuse “gas(E. guest)-vrye” vorm
te isoleer nie, het die werk ’n nuwe chirale gasheerraamwerk aan die lig gebring. Die
chirale gasheerraamwerk rig gas(E. guest)molekules in eendimensionele kolomme op
’n polêre wyse en gevolglik vertoon die materiaal nie-linieêre optiese eienskappe.
Hierdie resultaat is ongekend in die lang geskiedenis van kristalmanipulasie van
Dianin se verbindings en sy analoë. Hierdie afdeling beskryf ook die desorpsiestudies
van die nuwe gasheer, en die tiol-afgeleide van Dianin se verbinding. Die
sistematiese karakterisering van hierdie fases na desorpsie het fundamentale vrae na
vore gebring oor desorpsieprosesse oor die algmeen.
Die tweede afdeling maak die grootste gedeelte van die werk uit. ’n Reeks verwante
isostrukturele ringvormige koördinasieverbindings is gesintetiseer en hul struktuureienskap
verhoudings is deur ’n verskeidenheid komplementêre tegnieke ondersoek.
Hierdie metallosiklieseverbindings kristalliseer almal in gesolveerde toestand vanaf
sintese en verskillende resultate word verkry wanneer die verbinding desorpsie
ondergaan. In alle gevalle vind gas(E. guest)desorpsie as enkel-kristal na enkel-kristal
omsettings plaas en drie nuwe ‘oënskynlik nie-poreuse’ poreuse materiale is bekom.
’n Enkelkristal diffraksiestudie onder verskeie gasdrukke is met asetileen en
koolstofdioksied uitgevoer vir een van die poreuse metallosiklieseverbindings. Dit het die geleentheid geskep om die mate waartoe die gasheer as gevolg van verhoogde
ewewigsdruk vervorm (en dus toename in gasheerbesetting), sistematies te bestudeer.
Die waargenome verskille in sorpsie-optrede vir asetileen en koolstofdioksied word
bespreek en verklaar. Gravimetriese gassorpsie isoterme is ook vir die drie poreuse
materiale verkry en die diffusie van groter molekules deur die gasheer is struktureel
ondersoek. Laastens word ’n moontlike gasoordragmeganisme vir hierdie tipe
poreuse (i.e. oënskynlik nie-poreuse) materiale gepostuleer. Hierdie bespreking word
deur termodinamiese en kinetiese studies aangevul, sowel as molekulêre-meganika en
statisties-meganiese studies.
30
Acartürk, Ayhan. "Simulation of charged hydrated porous materials." Essen VGE, 2009. http://d-nb.info/998591939/04.
Full text
31
Thompson, Benjamin Robert. "Hierarchically structured composites and porous materials." Thesis, University of Hull, 2017. http://hydra.hull.ac.uk/resources/hull:16570.
Full textAbstract:
This thesis develops a hydrogel bead templating technique for the preparation of hierarchically structured composites and porous materials. This method involves using slurries of hydrogel beads with different size distributions as templates. Mixing hydrogel beads with a scaffolding material and then allowing the scaffold to harden, followed by drying of the composite leaves pores in the place of the hydrogel beads. These pores reflect the size and shape of the templates used and the porosity reflects the volume percentage of hydrogel bead slurry mixed with the scaffolding material. A viscous trapping technique has been developed which utilises the viscosity of methylcellulose to stop sedimentation of the scaffold particles during network formation. Both of these methods are attractive due to being cheap, non-toxic and they use food grade materials which allows their use in a multitude of applications. Porous and hierarchically porous gypsum composites have been prepared using both hydrogel bead templating and viscous trapping techniques, or a combination of the two. The level of control over the final microstructure of the dried composites offered by these techniques allowed for a systematic investigation of their thermal and mechanical properties as a function of the pore size, porosity and hierarchical microstructure. It has been shown that the thermal conductivity decreases linearly with increasing porosity, however it was not dependent on the pore sizes that were investigated here. The mechanical properties, however, were significantly different. The porous composites produced with either small hydrogel beads (100 μm) or methylcellulose solution had approximately twice the compressional strength and Young’s modulus compared to the ones produced with large hydrogel beads (600 μm). The sound insulating properties of porous and hierarchically porous gypsum composites have also been investigated. With increasing porosity, the sound transmission loss decreases, as expected. At constant porosity, it is shown that the composites with large pores perform significantly better than the ones with small pores in the frequency range of 75-2000 Hz. At higher frequencies (>2400 Hz) the composites with smaller pores begin to perform better. The material’s microstructure has been studied in an attempt to explain this effect. The hydrogel templating technique can be used to prepare composite materials if the drying step is not performed. Hydrogel beads have been incorporated into a soap matrix. The dissolution rate of these composites as a function of hydrogel bead size and volume percentage of hydrogel beads incorporated within the soap matrix has been investigated. It has been shown that the dissolution rate can be increased by increasing the volume percentage of hydrogel beads used during composite preparation but it is independent on their size distribution. Finally, three methods of controlling the release rate of encapsulated species from these soap-hydrogel bead composites have been shown. The first method involved varying the size distribution of the hydrogel beads incorporated within the soap matrix. The second involved changing the concentration of the gelling polymer and the final method required co-encapsulation of an oppositely charged polyelectrolyte. A binary hydrogel system has been developed and its rheological and thermal properties have been investigated. It consists of agar and methylcellulose and shows significantly improved rheological properties at high temperatures compared to agar alone. The storage modulus of the two component hydrogel shows a maximum at 55 °C which was explained by a sol-gel phase transition of methylcellulose, evidence of which was seen during differential scanning calorimetry measurements. After exposure of this binary hydrogel to high temperatures above the melting point of agar alone (> 120 °C), it maintains its structure. This suggests it could be used for high temperature templating or structuring of food products. The melt-resistant binary hydrogel was used for the preparation of pancake-hydrogel composites using hydrogel bead templating. Mixing slurry of hydrogel beads of this composition with pancake batter, followed by preparation at high temperatures produced pancakes with hydrogel beads incorporated within. Bomb calorimetry measurements showed that the caloric density could be reduced by a controlled amount by varying the volume percentage of hydrogel beads used during preparation of the composites. This method could be applied to other food products such as biscuits, waffles and breakfast bars. Furthermore, there is scope for development of this method by the encapsulation of flavour enhancing or nutritionally beneficial ingredients within the hydrogel beads.
32
Haubensak, Frederick G. (Frederick George). "Microstructure design of porous brittle materials." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/26876.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.<br>Includes bibliographical references (leaves 214-223).<br>by Frederick George Haubensak.<br>Ph.D.
33
McMonagle, Charles James. "Effect of pressure on porous materials." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31504.
Full textAbstract:
Research to design and synthesise new porous materials is a rapidly growing field with thousands of new systems proposed every year due to their potential use in a multitude of application in a wide range of fields. Pressure is a powerful tool for the characterisation of structure-property relationships in these materials, the understanding of which is key to unlocking their full potential. In this thesis we investigate a range of porous materials at a range of pressures. Over time the chemical architecture and complexity of porous materials has increased. Although some systems display remarkable stability to high-pressures, which we generally think of as being above 1 GPa (10,000 bar), in general, the compressibility of porous materials have increased substantially over the last 10 years, rendering most unstable at GPa pressures. Here we present new methods for investigating porous materials at much more moderate pressures (100's of bar), alongside more traditional high-pressure methods (diamond anvil cell techniques), finishing with gas sorption studies in a molecular based porous material. Here, the design and development of a new moderate pressure sapphire capillary cell for the small molecule beamline I19 at the Diamond Light Source is described. This cell allowed access to pressures of more than 1000 bar regularly with a maximum operating pressure of 1500 bar with very precise pressure control (< 10 bar) on both increasing and decreasing pressure. This cell closes the gap between ambient pressure and the lowest pressures attainable using a diamond anvil cell (DAC), which is generally above 0.2 GPa (2000 bar). Along with the development of the sapphire capillary pressure cell, the compression to 1000 bar of the small organic sample molecule Hexamethylenetetramine (hexamine, C6H12N4) and its deuterated form (C6D12N4) was determined, demonstrating the precision possible using this cell. Solvent uptake into porous materials can induce large structural changes at 100's of bar. In the case of the Sc-based Metal-organic framework (MOF), Sc2BDC3 (BDC = 1,4-benzenedicarboxylate), we used the sapphire capillary pressure cell to study changes in the framework structure on the uptake of n-pentane and isopentane. This work shows how the shape and smaller size of n-pentane facilitated the swelling of the framework that could be used to explain the increase in stability of the MOF to applied pressure. The effect of pressure on the previously unreported Cu-framework bis[1-(4- pyridyl)butane-1,3-dione]copper(II) (CuPyr-I) was investigated using high-pressure single-crystal diffraction techniques (DAC). CuPyr-I was found to exhibit high-pressure and low-temperature phase transitions, a pressure induced Jahn- Teller switch (which was hydrostatic medium dependent), piezochromism, and negative linear compressibility. Although each of these phenomena has been reported numerous times in a range of materials, this is to the best of our knowledge the first example to have been observed within the same material. The final two chapters investigate the exceptional thermal, chemical, and mechanical stability of a porous molecular crystal system (PMC) prepared by the co-crystallisation of a cobalt phthalocyanine derivative and a fullerene (C 60 or C70). The stabilising fullerene is captured in the cavity between two phthalocyanines in a ball and socket arrangement. These PMCs retain their porous structure: on the evacuation of solvent of crystalisation; on heating to over 500 K; on prolonged immersion in boiling aqueous acid, base, and water; and at extreme pressures of up to 5.85 GPa, the first reported high-pressure study of a PMC. the reactive cobalt cation is accessible via the massive interconnected voids, (8 nm3), as demonstrated by the adsorption and binding of CO and O2 to the empty metal site using in situ crystallographic methods available at beamline I19, Diamond Light Source.
34
Eder, Grace M. "Dye Molecule-Based Porous Organic Materials." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1530012900215452.
Full text
35
Farghaly, Ahmed A. "Fabrication of Multifunctional Nanostructured Porous Materials." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4189.
Full textAbstract:
Nanostructured porous materials generally, and nanoporous noble metals specifically, have received considerable attention due to their superior chemical and physical properties over nanoparticles and bulk counterparts. This dissertation work aims to develop well-established strategies for the preparation of multifunctional nanostructured porous materials based on the combination of inorganic-chemistry, organic-chemistry and electrochemistry. The preparation strategies involved one or more of the following processes: sol-gel synthesis, co-electrodeposition, metal ions reduction, electropolymerization and dealloying or chemical etching. The study did not stop at the preparation limits but extended to investigate the reaction mechanism behind the formation of these multifunctional nanoporous structures in order to determine the different factors controlling the nanoporous structures formation. First, gold-silica nanocomposites were prepared and used as a building blocks for the fabrication of high surface area gold coral electrodes. Well-controlled surface area enhancement, film thickness and morphology were achieved. An enhancement in the electrode’s surface area up to 57 times relative to the geometric area was achieved. A critical sol-gel monomer concentration was also noted at which the deposited silica around the gold coral was able to stabilize the gold corals and below which the deposited coral structures are not stable. Second, free-standing and transferable strata-like 3D porous polypyrrole nanostructures were obtained from chemical etching of the electrodeposited polypyrrole-silica nanocomposite films. A new reaction mechanism was developed and a new structural directing factor has been discovered for the first time. Finally, silver-rich platinum alloys were prepared and dealloyed in acidic medium to produce 3D bicontinuous nanoporous platinum nanorods and films with a nanoporous gold-like structure. The 3D-BC-NP-Pt displayed high surface area, typical electrochemical sensing properties in an aqueous medium, and exceptional electrochemical sensing capability in a complex biofouling environment containing fibrinogen. The 3D-BC-NP-Pt displayed high catalytic activity toward the methanol electro-oxidation that is 30 times higher that of planar platinum and high volumetric capacitance of 400 F/cm3. These findings will pave the way toward the development of high performance and reliable electrodes for catalysis, sensing, high power outputs fuel cells, battery-like supercapacitors and miniaturized device applications.
36
Richards, Emma. "Immobilisation of polyazamacrocycles into porous materials." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/8513/.
Full textAbstract:
The synthesis and characterisation of functionalised polyazamacrocycles and their subsequent immobilisation into porous materials were investigated and reported in this thesis. The incorporation of polyazamacrocycles into porous materials offers the potential to enhance their biomimetic and environmental properties with tuneable microenvironments around the macrocycles. Nine polyazamacrocycles have been synthesised that are functionalised with vinyl, pyridyl, carboxylate and iodide pendant arms in order to immobilise them into porous materials. Of these macrocycles nine metal complexes were successfully synthesised and their crystal structures are discussed. The most interesting of these metal complexes are complex 2, a cyclam based metal complex and complex 7, a [12]aneN3 based metal complex which both have coordinated water molecules and therefore are activated for hydrolase activity. Polyazamacrocycles have successfully been immobilised into organic cross-linked polymers using polar and non-polar cross-linkers and a systematic investigation has taken place in order to determine the effects of the nature and amount of porogen and the concentration of macrocycle within the polymer on the porous properties of the polymer. These effects include BET surface area, shape and size distributions of pores, and CO2 uptake capacities. The effect of incorporation of metal complexes and metal ions is also discussed. It was found that with non-polar based polymers, BET surface areas were find to be higher when non-polar porogens were employed and decrease with increasing polarity of the porogen. However, the nature of the macrocycle also plays an important role in the porosity of the resulting polymers. Zinc and copper metal organic frameworks containing cyclam based macrocycles with pyridyl pendent arms have been synthesised with 2D layered structures. The crystal structures reveal that triflate and hexafluorophosphate counterions play an important role in stabilisation of the framework but with the disadvantage of blocking possible porosity.
37
Cooper, Emma. "Renewable routes to porous aluminosilicate materials." Thesis, University of York, 2012. http://etheses.whiterose.ac.uk/3936/.
Full textAbstract:
The objectives of this project were to synthesise zeolites and aluminosilicate materials from silicon sources derived from biomass ashes. These materials will have great potential as catalysts and adsorbents. In order to begin this study it was necessary to find and optimise a technique for extraction of silicon to an alkali silicate solution from biomass ashes. It was then necessary to develop a technique for analysis of the alkali silicate solutions. This was done using calibration of integrals from infrared spectra. An optimisation of the synthesis of Zeolite X from a rice hull ash derived alkali silicate was developed and these materials were analysed and characterised using XRD, N2 Adsorption porosimetry, X‐Ray Fluorescence Spectroscopy, and X‐Ray Photoelectron Spectroscopy. An in‐depth study of the surface of the ash derived and reference Zeolite X was undertaken using in situ small molecule probing FT‐IR. It was found that although the materials were similar there was a significant difference due to the presence of a strongly bonded carbonate species in the pores of the bio‐derived zeolite. Synthesis of a Miscanthus ash derived mesoporous silica, MCM‐41, was successfully achieved which was comparable to its conventionally synthesised equivalent. Both displayed ordered hexagonal pores and high surface areas. A study on addition of different sources of aluminium found that it was possible to introduce aluminium into the structure successfully. Included in this study was the addition of the waste product ‘red clay’ as an aluminium source. Another mesoporous silica, SBA‐15 was synthesised from a Miscanthus ash derived alkali silicate. It was necessary to optimise the synthesis to adapt to the different pH systems of the conventional method and bio‐derived alkali silicate solutions. This was achieved and a bio‐derived SBA‐15 material with ordered hexagonal pores was produced.
38
Chow, Hon-nin. "Computer aided modelling of porous structures." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B39848929.
Full text
39
Jiran, Eva. "Capillary instabilities in thin, solid films." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14000.
Full text
40
Harter, Thomas. "Unconditional and conditional simulation of flow and transport in heterogeneous, variably saturated porous media." Diss., The University of Arizona, 1994. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1994_36_sip1_w.pdf&type=application/pdf.
Full text
41
Thatiparti, Deepthi Sharan. "Capillary pressure Measurement in Glass bead porous media and Gas diffusion layers." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1281450979.
Full text
42
Kou, Shuting, and 寇舒婷. "Porous structure modeling with computers." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206700.
Full textAbstract:
Porous structures are a particular type of solids, where a large number of pores exist in the geometric domain of interest. Research on porous structures have received increasingly keen interest in recent years and this is largely because of many unique and superior properties that porous structures possess. They can undertake special tasks which general solid materials are not competent to do.
In recent twenty years numerous representations are put forward for porous structure modeling. But the challenges in practical porous structure design still exist and the structure heterogeneity brings many difficulties. This thesis is motivated to propose new porous structure modeling strategies which are more accurate, flexible and easy for porous structure description.
An approach of porous structure modeling based on quadtree/octree and NURBS is proposed first. Quadtree and octree are tools for modeling domain partition. The pore size and pore distribution are controlled by the flexibility of quadtree and octree enumeration technique. Derived polygon and polyhedron are then introduced to assist the generation of NURBS curves and surfaces. These NURBS curves and surfaces form the boundaries of the porous structures.
However there are limitations of the above method. The accurate control of porosity is not easily achieved in 3D porous structure modeling and seemingly adopting quadtree/octree for the modeling domain partition is also less than satisfactory. Hence a new representation for porous structures based on Centroidal Voronoi tessellation (CVT) and pore-network is put forward. CVT is utilized for modeling domain partition because the CVT cells are approximate hexagons which is widely existent in plants, animals and other cellular structures in nature. The density distribution function used in CVT generation also helps to build functionally graded porous structures. Pore-network, which is a mature and commonly used model in the research of multiphase flow in porous media, is subsequently introduced to build the porous structures. This modeling approach results in porous structures that could mimic the geometry and performance of structures in nature.
To evaluate the object’s properties, finite element analysis (FEA) is conducted on the porous structure models represented by the two methods. The mechanics properties of the two types of models are analyzed. The stress-strain curve of each sample is plotted and the effective Young’s modulus is calculated. Comparison of these two types of models is also done. Besides, the contributions of the thesis and suggestions for future research are also discussed.<br>published_or_final_version<br>Mechanical Engineering<br>Master<br>Master of Philosophy
43
HAMDAN, MOHAMMAD OMAR. "LOOP HEAT PIPE (LHP) MODELING AND DEVELOPMENT BY UTILIZING COHERENT POROUS SILICION (CPS) WICKS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1049987207.
Full text
44
Mohamed, Rozita. "Preparation of nano-structured macro-porous materials." Thesis, University of Newcastle upon Tyne, 2011. http://hdl.handle.net/10443/1317.
Full textAbstract:
This research reveals a catalyst development towards achieving catalysts with hierarchical porous structures with enhanced mechanical properties by using nano-structured macro-porous PolyHIPE polymer. This work can be divided into two parts: the fabrication and its characterisation of hierarchical metal structure using PHP and other fibre materials; and the fabrication and characterisation of PHP with silica particles and glass wool, further coated with silane material as templates. A catalyst system was successfully fabricated forming a 3D-interconnecting network of pore size, ranging from tens of micrometers and gradually reducing finally to nanometer scale. An electroless deposition flow through method using Ni-B bath solution was performed on the templates and was subsequently heat treated to obtain porous metallic structures, thus providing accessibility for reactants to the surface and for products away from the surface. Meanwhile, silanated templates were produced by surface treatment. This was performed by submerging templates directly into the silanes solution at room temperature (24°C) using a water-ethanol based solution of the silanes. The polymer-metal/alloy or silica functionalized based composite demonstrated a high impact strength. The results showed that not only hierarchical pore structure was formed, but it was also demonstrated that silica particles were totally and uniformly covered/coated by metal deposit and had good adhesion. When used on glass wool, silanation had greatly improved the bond strengths of metal deposits to the templates. SEM micrographs revealed that the formation of cracks were tremendously reduced and exhibited higher bond strengths due to silanated glass surface. It is expected to be more efficient and robust in the case of an enhanced surface area, and most desirable in catalyst applications.
45
Ridgway, Catherine Jean. "Modelling pore-level properties of porous materials." Thesis, University of Plymouth, 1995. http://hdl.handle.net/10026.1/1707.
Full textAbstract:
Pore-Cor is a 1.2 Mbyte Fortran 77 software package, which uses information from mercury porosimetry curves, supported by image-analysed electron micrographs, to generate a three-dimensional representational model of the pore-space within a porous material. As a result of this project, a much-improved version has been produced. The mercury intrusion curves for the simulated structures now converge automatically onto the experimental curves, so reducing the simulation time from several days to less than an hour. A further time economy has been provided by the incorporation of an improved permeability routine, reducing the calculation time from 10 minutes to 30 seconds. Modifications have allowed non-homogeneous structures to be modelled, in simulation of real samples of banded, vuggy and clay-included sandstones. Porosimetry measurements have been made for Fontainebleau sandstone into which small amounts of illite, a simulated clay deposit, had been introduced by hydrothermal crystallisation. Despite having no effect on porosity, the effects on simulated permeability could be successfully assessed. The causes of hysteresis, i.e. the trapping of a non-wetting fluid in a porous medium, were also investigated. The need for higher quality experimental data to feed into the Pore-Cor software has led to improved measurement and analysis methods for the porosimetry. A new spreadsheet-based iterative programme, named Pore-Comp. provides a unique method of measuring the compressibility (or bulk modulus) of the solid phase of a porous medium, and this has been used to examine the effects of silicate micro-crystallinity and latex binders on the compressibility of paper-coating formulations. Using the cryo-stage of the electron microscope, the retention of mercury in some paper coating formulations has been investigated further.
46
Panella, Barbara. "Hydrogen storage by physisorption on porous materials." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-29012.
Full text
47
Wilcox, O. T. "Porous materials for the uptake of ammonia." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3007235/.
Full text
48
Littlefield, Benjamin T. R. "Solvothermal synthesis of porous beryllate containing materials." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/359297/.
Full textAbstract:
Natural and synthetic zeolites have been the focus for extensive research owing to their many applications and huge potential number of new topologies. The work presented here represents the first major study into the formation of zeotypical materials incorporating BeO4 and T5+O4 (T5+ = As or P) tetrahedra and a large number of new structures have been produced. These novel materials have been synthesised via hydrothermal procedures and characterised via Single Crystal X-ray Diffraction, supported by Powder X-ray Diffraction, Thermogravimetric Analysis, Magic Angle Spinning Nuclear Magnetic Resonance and Electron Dispersive Spectroscopy. The berylloarsenates produced encompass the entire range of dimensionality, from cluster structures such as Na3.5[AsO4(BeF3)(BeF2)]•0.4H2O to the novel three dimensional framework [Hbis( 2-ethylhexyl)amine, NH4] [(AsO4)3(AsO3OH)Be3(BeOH)] and include analogues of known zeolite topologies; MER, AFI and WEI. Four completely novel fully connected three-dimensional zeolitic topologies are also reported with one already being assigned the Framework Type code of BOZ. These new topologies represent the most structurally complicated zeolites known and are remarkable in their high calculated internal pore volume. The berylloarsenates are supported by parallel research into the beryllophosphates which has produced unusual new structures of low dimensionality such as the one dimensional chain Na2[(BeO2OH)(PO2)]•H2O as well as structural analogues of the berylloarsenate structures including [H-pyridine][(BeO4)2BeO3(OH2)P3(OH)] which exhibits the AFI topology. These structures could potentially be used in catalysis, ion exchange and due to their low framework density, gas storage. A short investigation into other beryllate chemistry is also presented which includes the novel two dimensional structures Na[BeGeO3(OH)] and Ba[BeGeO3(OH)] which significantly contribute to the sparse field of beryllogermanates. This section also contains the first structural characterisation of Sr[Be(OH)4], a vital species in beryllium solution chemistry.
49
Kunjir, Shrikant. "Study of new porous materials by NMR." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC211/document.
Full textAbstract:
Les zéolites sont des «tamis moléculaires» connus pour leurs nombreuses applications en adsorption, échange d'ions et catalyse. Dans cette thèse, nous nous sommes concentrés sur l'étude de quelques questions liées à la synthèse et à la post-synthèse de la zéolithe, qui ne sont pas encore résolues par d'autres techniques.La RMN a été l'outil principal dans ce travail, donnant accès à des informations structurales locales sur les nanocristaux même lorsque les techniques de diffraction trouvent leurs limites. Elle peut également être utilisée pour étudier la porosité en utilisant l'adsorption de molécules sondes, et en particulier, le xénon est connu comme une bonne molécule pour cet objectif. En effet, l'isotope 129Xe peut être hyperpolarisé pour augmenter la sensibilité de détection, et il présente une large plage de déplacement chimique en fonction du confinement et donc de la porosité du matériau étudié.(I) Dans la première étude, les étapes initiales de la cristallisation de nano-faujasite (FAU) ont été étudiées en utilisant la RMN classique (principalement par 29Si et 23Na MAS RMN) et la RMN avancée (129Xe). RMN HP). Il a été montré que la cristallisation commence à des stades de synthèse bien antérieurs à ceux observés par d'autres techniques classiques (XRD, SEM, adsorption de N2 ...). La première SBU semble être les prismes hexagonaux, avant les cages sodalite, qui forment rapidement un environnement confiné puis des supercages. De plus, il a été démontré par RMN 129Xe HP et 2D EXSY que la zéolithe nano-faujasite présente des cages sodalite ouvertes et une structure plus souple que dans la zéolite de type micro-faujasite.(ii) La seconde étude est une recherche sur les phénomènes de recristallisation survenant au cours du processus de hiérarchisation de la zéolithe et qui pourrait expliquer la distribution homogène des tailles de mésopores. Comme résultat remarquable, il a été montré dans ce travail que lors de la hiérarchisation de la zéolithe bêta avec le TPAOH, la recristallisation conduisait à la formation de minuscules particules de MFI, formées à la surface des mésopores (RMN 1H MAS, RMN 129Xe HP et 2D EXSY)<br>The zeolites are ‘molecular sieves’ known for their numerous applications in adsorption, ion exchange, and catalysis. In this thesis, we focused on the study of some questions related to zeolite synthesis and post-synthesis, which are not yet resolved by other techniques. NMR was the primary tool in this work, as it gives access to local structural information on nanocrystals even when diffraction techniques found their limits. NMR can also be used to study porosity using probe molecules adsorption, and in particular, xenon is known as a good molecule for this purpose. Indeed, the isotope 129Xe can be hyperpolarized to increase the detection sensitivity, and interestingly it presents a wide chemical shift range depending on its confinement and thus the porosity of studied material. Two studies are reported in this manuscript: (i) In the first study, the initial steps during the crystallization of nano-faujasite (FAU) type materials were investigated using classical NMR (mainly by 29Si and 23Na MAS NMR) and advanced NMR (129Xe HP NMR). It was shown that crystallization starts at much earlier synthesis stages than those observed by other classical techniques (XRD, SEM, N2 adsorption…). The first SBU seems to be the hexagonal prisms, prior to the sodalite cages, which rapidly form confined environment and then supercages. Moreover, it has been proved by 129Xe HP NMR and 2D EXSY that nano-faujasite zeolite presents opened sodalite cages and a more flexible structure than in micro-faujasite zeolite. (ii) The second study is an investigation on the recrystallization phenomena occurring during hierarchization process of zeolite and which could explain the homogenous distribution of the mesopore sizes. As a remarkable result, it has been shown in this work that during the hierarchization of beta zeolite with TPAOH, the recrystallization lead to the formation of tiny MFI particles, formed at the surface of the mesopores (1H MAS NMR, 129Xe HP NMR and 2D EXSY)
50
Cervin, Nicholas. "Porous Cellulose Materials from Nano Fibrillated Cellulose." Licentiate thesis, KTH, Fiberteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-104196.
Full textAbstract:
In the first part of this work a novel type of low-density, sponge-like material for the separation of mixtures of oil and water has been prepared by vapour deposition of hydrophobic silanes on ultra-porous nanocellulose aerogels. To achieve this, a highly porous (> 99 %) nanocellulose aerogel with high structural flexibility and robustness is first formed by freeze-drying an aqueous dispersion of the nanocellulose. The density, pore size distribution and wetting properties of the aerogel can be tuned by selecting the concentration of the nanocellulose dispersion before freeze-drying. The hydrophobic light-weight aerogels are almost instantly filled with the oil phase when they selectively absorb oil from water, with a capacity to absorb up to 45 times their own weight. The oil can also be drained from the aerogel and the aerogel can then be subjected to a second absorption cycle.In the second part of the work a novel, lightweight and strong porous cellulose material has been prepared by drying aqueous foams stabilized with surface-modified NanoFibrillated Cellulose (NFC). Confocal microscopy and high-speed video imaging show that the long-term stability of the wet foams can be attributed to the octylamine-coated, rod-shaped NFC nanoparticles residing at the air-liquid interface which prevent the air bubbles from collapsing or coalescing. Careful removal of the water yields a porous cellulose-based material with a porosity of 98 % and a density of 30 mg cm-3. These porous cellulose materials have a higher Young’s modulus than other cellulose materials made by freeze drying and a compressive energy absorption of 56 kJ m-3 at 80 % strain. Measurements with an autoporosimeter reveal that most pores are in the range of 300 to 500 μm.<br><p>QC 20121107</p>