The classical Terzaghi Theory was extended by accounting for the variations of permeability during consolidation. With the aid of X-ray techniques, investigations on the significance of the variation of permeability, as well as the variations of void ratio and effective pressure, were conducted. Effects of the conventional consolidometer boundary on consolidation testing were studied. / Thesis / Master of Engineering (ME)

Thesis. 1978. Sc.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Vita. / Bibliography: leaves 212-219. / by Cheng, Chuen Hon Arthur. / Sc.D.

A series of mixed matrix membranes based on zeolites incorporated into fluorinated polyimides were fabricated and characterized in this study. The first system consisted of a polyimide (6FDA-6FpDA-DABA) with carboxylic acid groups incorporated into its backbone and amine-functionalized zeolite particles (ZSM-2). FTIR indicated that these functional groups interacted with each other through hydrogen bonding. Both SEM and TEM images revealed good contact between the polyimide and the zeolite. Permeability studies showed a drop in He permeability suggesting there were no voids between the two components. While simple gases such as O2 and N2 followed effective permeabilities predicted by mixing theories, polar gases such as CO₂ did not. The second system fabricated used the same polyimide with amine-functionalized zeolite L. This zeolite differs from ZSM-2 in that zeolite L's pores are not clogged with an organic template, and it possesses 1-D pores as opposed to ZSM-2's 3-D pore structure. XPS and zeta potential experiments were performed to verify the presence of amine groups on the zeolite surfaces. FTIR data showed that after a heat treatment, amide linkages were created between the amine group on the zeolite and the carboxylic acid group of the polyimide. SEM images showed a good distribution of zeolite L throughout the polymer matrix, and no indication of voids between the two components. Permeability experiments were performed to determine if the addition of zeolite L to the polyimide improved its separation performance. The permeability was unchanged between the pure polyimide membrane and the mixed matrix membrane, suggesting there were no voids present within the matrix. Permeability results of larger gases followed a Maxwell Model. A third system was prepared using a poly(imide siloxane) (6FDA-6FpDA-PDMS) and untreated zeolite L. The primary focus of this investigation was to determine if the addition of the flexible segment would promote direct contact with the zeolite surface and remove the need to amine-functionalize the zeolite. Poly(imide siloxane)s were synthesized at 0, 22, and 41 wt % PDMS as verified using 1H-NMR. FTIR was employed to qualitatively verify the successful imidization of the polymers. SAXS patterns and TEM images did not reveal distinct phases indicative of phase separation, however, AFM images did show the presence of phase separation of the surfaces of the poly(imide siloxane)s. Permeability results showed a decrease in selectivity and an increase in permeability as the wt % of PDMS was increased. Permeabilities and selectivities dropped as the zeolite loading was increased from 0 to 20 wt %. Upon increasing the zeolite loading from 20 to 30 wt %, increases in permeability were observed, but both the permeability and selectivity were still below that of the pure polymer. The final system studied employed the 41 wt % PDMS poly(imide siloxane) as the polymer matrix and either closed-ended or open-ended carbon nanotubes as the filler. SEM images showed regions of agglomeration for both types of nanotubes. Helium permeability dropped in both types MMMs, but more so in closed-ended carbon nanotubes MMM. Nitrogen permeability was unchanged for the closed-ended carbon nanotubes MMM, and dropped slightly in the open-ended carbon-nanotube MMM. / Ph. D.

This work was performed under a cooporative research effort sponsored by the National Aeronautics and Space Administration (NASA) in conjunction with the aerospace industry and acedemia. One of the primary goals of NASA is to improve the safety and affordability of commercial air flight. Part of this goal includes research to reduce fuel consumption by developing lightweight carbon fiber, polymer matrix composites to replace existing metallic airframe structure. In the Twenty-first Aircraft Technology Program (TCAT) efforts were focused on developing novel processing methods to fabricate tailored composite airframe structure. The Vacuum Assisted Resin Transfer Molding (VARTM) processing technique offers a safer, more affordable alternative to manufacture large scale composite fuselages and wing structures. Vacuum assisted resin transfer molding is an infusion process originally developed for manufacturing of composites in the marine industry. The process is a variation of Resin Transfer Molding (RTM), where the rigid matched metal tooling is replaced on one side with a flexible vacuum bag. The entire process, including infusion and consolidation of the part, occurs at atmospheric pressure (101.5 kPa). High-performance composites with fiber volumes in the range of 45% to 50% can be achieved without the use of an autoclave. The main focus of the VARTM process development effort was to determine the feasibility of manufacturing aerospace quality composites with fiber volume fractions approaching 60%. A science-based approach was taken, utilizing finite element process models to characterize and develop a full understanding of the VARTM infusion process as well as the interaction of the constituent materials. Achieving aerospace quality composites requires further development not only of the VARTM process, but also of the matrix resins and fiber preforms. The present work includes an investigation of recently developed epoxy matrix resins, including the characterization of the resin cure kinetics and flow behaviors. Two different fiber preform architectures were characterized to determine the response to compaction under VARTM conditions including a study to determine the effect of thickness on maximum achievable fiber volume fraction. Experiments were also conducted to determine the permeabilities of these preforms under VARTM flow conditions. Both the compaction response and the permeabilities of the preforms were fit to empirical models which can be used as input for future work to simulate VARTM infusion using process models. Actual infusion experiments of these two types preforms were conducted using instrumented tools to determine the pressures and displacements that occur during VARTM infiltration. Flow experiments on glass tooling determined the fill-times and flow front evolution of preform specimens of various thicknesses. The results of these experiments can be used as validation of process model infusion simulations and to verify the compaction and permeability empirical models. Panels were infused with newly developed epoxy resins, cured and sectioned to determine final fiber volume fractions and part quality in an effort to verify both the infusion and compaction experimental data. The preforms characterized were found to have both elastic and inelastic compression response. The maximum fiber volume fraction of the knitted fabrics was dependent on the amount of stacks in the preform specimen. This relationship was found in the determination of the Darcy permeabilities of the preforms. The results of the characterization of the two epoxy resin systems the show that the two resins have similar minimum viscosities but significantly different curing behaviors. Characterization of the VARTM process resulted in different infusion responses in the two preform specimens investigated. The response of the saturated preform to a recompaction after infusion indicated that a significant portion of the fiber volume lost during infusion could be recovered. Fiber volume and void-content analysis of flat composite panels fabricated in VARTM using the characterized resins and preforms resulted in void-free parts with fiber volumes over 58%. Results in the idealized compaction tests indicated fiber volumes as high as 60% were achievable with the knitted fabric. The work over the presented here has led to a more complete understanding of the VARTM process but also led to more questions concerning its feasibility as an aerospace composite manufacturing technique. / Master of Science

Electroporation-based treatments are motivated by the response of biological membranes to high- intensity pulsed electric fields. These fields rearrange the membrane structure to enhance the membrane's diffusive permeability, or the degree to which a membrane allows molecules to diffuse through it, is impacted by the structure, composition, and environment in which the cell resides. Tracer molecules have been developed that are unable to pass through intact cell membranes yet enter permeabilized cells. This dissertation investigates the hypothesis that the flow of such molecules may be used to quantify the effects of the electrical stimulus and environmental conditions leading to membrane electroporation. Specifically, a series of electrical pulses that alternates between positive and negative pulses permeabilizes cells more symmetrically than a longer pulse with the same total on-time. However, the magnitude of this symmetric entry decreases for the shorter alternating pulses. Furthermore, a method for quantitatively measuring the permeability of the cell membrane was proposed and validated. From data near the electroporation threshold, the response of cells varies widely in the manner in which cells become permeabilized. This method is applied to study the transient cell membrane permeability induced by electroporation and is used to demonstrate that the cell membrane remains permeable beyond 30 min following treatment. To analyze these experimental findings in the context of physical mechanisms, computational models of molecular uptake were developed to simulate electroporation. The results of these simulations indicate that the cell's local environment during electroporation facilitates the degree of molecular uptake. We use these models to predict how manipulating both the environment of cells during electroporation affects the induced membrane permeability. These experimental and computational results provide evidence that supports the hypothesis of this dissertation and provide a foundation for future investigation and simulation of membrane electroporation. / PHD

Hydrothermal systems associated with oceanic spreading centers account for a quarter of Earth's total heat flux and one third of the heat flux through the ocean floor. Circulation of seawater through these systems alters both the crust and the circulating fluid, impacting global geochemical cycles. The warm vent fluids rich in nutrients support a wide variety of unique biological communities. Thus, understanding hydrothermal processes at oceanic spreading centers is important to provide insight into thermal and biogeochemical processes. In this dissertation I present the results of numerical modeling efforts for mid-ocean ridge hydrothermal systems. In the three manuscripts presented, permeability emerges as a key controlling factor for hydrothermal venting. In the first manuscript, I use 2-D numerical models to find that the distribution of permeability in the crust controls fluid velocity as well as the amount of mixing between hot hydrothermal fluids and cold seawater. This, in turn, effects the temperature and composition of fluids emerging on the surface. For the second manuscript, I construct single-pass 1-D models to show that a sudden increase in permeability caused due to magmatic or seismic events in the seafloor causes a sharp rise in the fluid output of the system. This, in conjunction with steep thermal gradients close to the surface, results in a rapid increase of venting temperatures. In the third manuscript, I develop a particle tracking model to study fluid trajectories in the subsurface. The results show that permeability distribution in the subsurface governs fluid paths and consequently, the residence time of fluids in the crust. Based on the work presented in this document, I conclude that permeability distribution, both local and field scale, exerts a major control on hydrothermal circulation in the subsurface and on the temperature and composition of venting fluids on the surface. / Ph. D.

The longitudinal air permeabilities of the wood of 1116 specimens from 279 trees, two sapwood and two heartwood replicates, representing two varieties of lodgepole pine (Pinus contorta, vars. latifolia and murrayana) were measured with a steady state apparatus. It was found that the mean ratio of sapwood to heartwood permeability was ca. 10:1 for both varieties. The mean ratio of var. latifolia to murrayana was 1.5:5 and 1.75:5 for sapwood and heartwood, respectively. The most important source of variation following the difference between heartwood and sapwood was that among trees. Geographical locations, such as latitude and elevation did not significantly influence permeability. Tree size did, but only because the small trees (3 inch diameter) showed higher heartwood permeability and lower sapwood permeability than normal. Ca. 20 specimens of latifolia heartwood showed extremely high permeabilities. They were also deeply brown in color, which probably was caused by fungal or bacterial infestation. Pit pore size and number per cm² were determined for sapwood by making four permeability measurements, each at a different average pressure on each specimen. A mean pit pore radius of 1.5 µm and 1.3 µm for sapwood of var. latifolia and var. murrayana was calculated. The median values between 1200-1300 pit pores per cm² indicate an average rate of tracheid connection of 1.2-1.3%. Of the tested wood parameters including moisture content and specific gravity average ringwidth, only the permeability of var. latifolia was significantly correlated with moisture content for both heartwood and sapwood, with a negative correlation coefficient. Water retention measurements were carried out to relate the measured gas permeability of an individual specimen to its ability to absorb water. For both varieties the retention was significantly and quadratically correlated with sapwood permeability (R² = 0.286 and 0.224) and was linearly correlated with heartwood permeability (R² = 0.488 and 0.5775). The correlation factors for the regression between retention and the logarithm of permeability were 0.239 and 0.227 for sapwood and 0.447 and 0.420 for heartwood. / M.S.

M.S.

The placenta is a highly vascularized, temporary organ developed in pregnancy that is composed of both maternal and fetal cells. It plays a pivotal role in gestational health by facilitating embryo implantation and fostering nutrient exchange between mother and fetus. Placental malformation and the diffusion of harmful exogenous substances through the placental barrier can cause pregnancy complications and, in more severe cases, death of the mother or the fetus. Further, the placenta undergoes profound morphological and functional changes throughout pregnancy. Establishing models to mimic these phenomena at different stages of pregnancy informs prescription drug safety and expedites the development of placental disease treatments. Mouse models are often used to simulate human fetal development despite major interspecies differences. These limitations drive researchers to developing in vitro models consisting of human-derived cells. This thesis presents three 3D vascularized placental models utilizing human placental stem cells (PSCs) and human umbilical vein endothelial cells (HUVECs) which can model multiple placental phenomena across early- and late-stage pregnancy. The first model features a 3D fibrin hydrogel network with self-assembled vasculature and a monolayer of syncytialized human trophoblastic stem cells (STs) serving as a platform for barrier studies at the maternal-fetal interface. By tuning trophoblast differentiation and vascularization of this model to mimic the early- and late-stage placenta, it was revealed that placental barrier permeability was dependent on placental maturity and that the vascular barrier is also a critical determinant of what molecules can be passed from the mother to the fetus. The design and manufacturing of this model were then streamlined to meet the demands of large-scale drug studies in the second placental barrier model. Placental invasion into the maternal decidua is carefully orchestrated by multiple cell types to prevent over- and under-invasion, both of which can be dangerous to the mother and fetus. Understanding the biochemical and environmental cues that permit this healthy invasion can allow for improved diagnostics and treatments of placental diseases, such as preeclampsia and placenta accreta. Thus, the third model presented herein is a placental invasion model with chorionic villus-like structures seeded with invasive extravillous cytotrophoblasts (EVTs) and a perfusable vascular channel. Collectively, these models facilitate the exploration of placental morphogenesis and function throughout various stages of pregnancy. They offer a valuable tool for probing placental dysfunctions and assessing drug safety, ultimately contributing to advancements in fetal-maternal health. / Thesis / Doctor of Philosophy (PhD) / The placenta is an essential organ in pregnancy and is responsible for a variety of phenomena that assure the survival of the fetus. However, many women suffer from negative pregnancy outcomes due to placental disorders, such as preeclampsia, or due to the crossing of unsafe compounds through the placenta to the fetus. Trophoblasts are the most notable placental cell type originating from the fetus and they have the capacity to mature into more specialized subtypes that are responsible for placental barrier function and placental development via invasion into the maternal tissue. In this work, we have designed three systems that either model placental barrier function or trophoblast invasion by culturing primary endothelial cells with differentiated trophoblast cells on a gel-based device. Using the barrier models, it is possible to assess the rate of transport of different compounds that may be present in the mother’s blood to the fetus, to assess their safety. Whereas the invasion model has the capacity to model the genesis of the placenta and therefore may be used to shed light on the causes for placental dysfunctions at the early stage of pregnancy.

Carbon capture and sequestration (CCS) is an engineering-based approach for mitigating excess anthropogenic CO2 emissions. Deep brine aquifers and basalt reservoirs have shown outstanding performance in CO2 storage based on their global widespread distribution and large storage capacity. Capillary trapping and mineral trapping are the two dominant mechanisms controlling the distribution, migration, and transportation of CO2 in deep brine aquifers and basalt reservoirs. Understanding the behavior of CO2 in a storage reservoir under realistic conditions is important for risk management and storage efficiency improvement. As a result, numerical simulations have been implemented to understand the relationship between fluid properties and multi-phase fluid dynamics. However, the physics-based simulations that focus on the uncertainties of fluid flow dynamics are complicated and computationally expensive. Machine learning method provides immense potential for improving computational efficiency for subsurface simulations, particularly in the context of parametric sensitivity. This work focuses on parametric uncertainty associated with multi-phase fluid dynamics that govern geologic CO2 storage. The effects of this uncertainty are interrogated through ensemble simulation methods that implement both physics-based and machine learning modeling strategies. This dissertation is a culmination of three projects: (1) a parametric analysis of capillary pressure variability effects on CO2 migration, (2) a reactive transport simulation in a basalt fracture system investigating the effects of carbon mineralization on CO2 migration, and (3) a parametric analysis based on machine learning methods of simultaneous effects of capillary pressure and relative permeability on CO2 migration. / Doctor of Philosophy / Carbon capture and sequestration (CCS) has been proposed as a technological approach to mitigate the deleterious effects of anthropogenic CO2 emissions. During CCS, CO2 is captured from power plants and then pumped in deep geologic reservoirs to isolate it from the atmosphere. Deep sedimentary formations and fractured basalt reservoirs are two options for CO2 storage. In sedimentary systems, CO2 is immobilized largely by physical processes, such as capillary and solubility trapping, while in basalt reservoirs, CO2 is transformed into carbonate minerals, thus rendering it fully immobilized. This research focuses on how a large range of capillary pressure variabilities and how CO2-basalt reactions affect CO2 migration. Specifically, the work presented utilizes numerical simulation and machine learning methods to study the relationship between capillary trapping and buoyancy in a sandstone formation, as well as the combined effects of capillary pressure and relative permeability on CO2 migration. In addition, the work also identifies a new reinforcing feedback between mineralization and relative permeability during reactive CO2 flow in a basalt fracture network. In aggregate, the whole of this work presents a new, multi-dimensional perspective on the multi-phase fluid dynamics that govern CCS efficacy in a range of geologic formations.