Browsing by Subject "Confinement"
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Item Design, synthesis, and engineering of advanced materials for block copolymer lithography(2015-05) Durand, William John; Willson, C. Grant, 1939-; Ellison, Christopher J.; Bonnecaze, Roger T; Truskett, Thomas M; Akinwande, DejiBlock copolymers (BCPs) are an attractive alternative for patterning applications used to produce next-generation microelectronic devices. Advancements require the development of high interaction parameter χ BCPs that enable patterning at the sub-10 nm length scale. Several organosilicon BCPs were designed to both enhance χ and impart an inherent etch selectivity that facilitates pattern transfer processes. Increasing the BCP silicon content both increases χ and bolsters the etch resistance, providing a pathway to designing new high-χ materials. Unfortunately, the BCPs investigated are not amenable to thermal annealing because the organosilicon block preferentially segregates to an air/vacuum interface and drives orientation parallel to the surface. A series of spin-coatable, polarity-switching top coats (as well as other strategies) were developed to provide a “neutral” top interface and promote the perpendicular orientation of BCP domains. In addition, a methodology for evaluating the neutral condition, relying on thickness quantization and the corresponding wetting behavior (i.e. island/hole topography) of lamellae. The top coat strategy was demonstrated for several BCP systems, and perpendicular structures can successfully be etched on commercial tools and be transferred into underlying substrates. The interaction parameter χ was evaluated using two methods to compare the performance of several BCPs: the order-disorder transition (ODT) of symmetric diblock copolymers, and the absolute scattering profile of a disordered BCP melt. Both methods, while severely limited for quantitative comparison, indicate trends towards higher χ with additional appended polar and organosilicon functional groups. Furthermore, the pattern fidelity is shown to be a function of the overall BCP segregation strength. The free energy of confined lamella was modeled algebraically to produce response surface plots capable of identifying process conditions favorable for perpendicular orientation. Thickness independent perpendicular orientation is only favorable using two neutral interfaces. Incommensurate film thicknesses are the most favorable, with commensurability conditions dependent on the wetting behavior at each interface. The modeling was supplemented with an extensive body of thin film experimental work that qualitatively agrees well with the above conclusions.Item Development of a Thermodynamic Model for Fluids Confined in Spherical Pores(2014-07-18) D'Lima, Michelle LynnThe thermodynamic properties of a fluid confined in extremely small pores can be substantially different from those observed of the same bulk fluid. These differences in behavior could have technical applications in adsorption-based separations; may pose a challenge with regards to the extraction of oil entrapped in the small cavities of reservoir rocks; or could even be utilized in complex heterogeneous catalytic systems such as those used in gas-to liquid fuel conversions. This thesis describes the use of the generalized van der Waals theory to extend cubic equations of state, such as Peng-Robinson, that are widely applied in the oil and gas industry to model the behavior of pure fluids as well as mixtures confined in spherical pores. Empirical expressions were developed for the coordination number in spherical pores as a function of the molecule to pore size ratio, for the distribution of molecules along the pore radius as function of temperature, and of the interaction potential between the molecules and the pore wall. Despite their relative simplicity, the expressions capture the limiting behaviors expected at high and low temperatures. The model parameters were then fitted to experimental data for the adsorption of light hydrocarbons and gases in common adsorbents. Finally, the calculated results were compared to the experimental results in order to assess the performance of the model, through adsorption equilibrium calculations.Item Effect of confinement on shear dominated reinforced concrete elements(Texas A&M University, 2005-02-17) Powanusorn, SuraphongIt has been demonstrated that transverse reinforcement not only provides the strength and stiffness for reinforced concrete (RC) members through direct resistance to external force demands, but also helps confine the inner core concrete. The confinement effect can lead to improved overall structural performance by delaying the onset of concrete fracture and allowing more inelastic energy dissipation through an increase in both strength and deformability of RC members. The objective of this research was to evaluate the effect of confinement due to the transverse reinforcement on enhancing the shear performance of RC members. A new constitutive model of RC members was proposed by extending the Modified Compression Field Theory (MCFT) to incorporate the effect of confinement due to transverse reinforcement by adjusting the peak stress and peak strain of confined concrete in compression. The peak stress of confined concrete was determined from the five-parameter failure surface for concrete developed by Willam and Warnke (1974). The peak strain adjustment was carried out using a relationship proposed by Mander et al. (1988). The proposed analytical model was compared with results from an experimental program on sixteen RC bent caps with varied longitudinal and transverse reinforcement details. Two-dimensional Finite Element Modeling (FEM) using the proposed constitutive model was conducted to numerically simulate the RC bent cap response. Results showed that the proposed analytical model yielded good results on the prediction of the strength but significantly overestimated the post-cracking stiffness of the RC bent cap specimens. The results also indicated that the confinement effect led to enhanced overall performance by increasing both the strength and deformability of the RC bent caps. Two potential causes of the discrepancy in the underestimation of the RC bent cap deformations, namely the effects of concrete shrinkage and interfacial bond-slip between the concrete and main flexural reinforcement in the bent caps, were discussed. Parametric studies showed that the tension-stiffening in the proposed constitutive models to implicitly take into account the bond-slip between the concrete and main flexural reinforcement was the major cause of the overestimation of the post-cracking stiffness of RC bent caps. The explicit use of bond-link elements with modified local bond stress-slip laws to simulate the slip between the concrete and main flexural reinforcement led to good predictions of both strength and deformation.Item Effects of nanoconfinement on structure and properties of side-chain liquid crystalline polymers(2013-12) Gonzalez Garza, Paola Anaid; Ellison, Christopher J.Semi-crystalline polymers have shown increased crystalline order and size when confined in multilayered films by coextrusion1. The resulting large crystals lead to dramatic improvements in gas barrier properties. Ordered polymers whose characteristics are between that of the liquid phase and the crystalline phase are known as liquid crystalline polymers. The highly ordered mesogens in liquid crystalline polymers contribute to their exceptional bulk properties. In this research, side-chain liquid crystalline polymers were confined in multilayered films, made by either multilayer coextrusion or spin coating, with a non-liquid crystalline polymer in an attempt to improve the ordering of the liquid crystalline mesogens. The liquid crystalline behavior and morphology was studied to understand the correlation between the confinement size and the properties of the multilayer films. Commercial main chain liquid crystalline polymers and hydrogen bonded liquid crystalline polymers were also explored in this research for their use in multilayer coextrusion.Item Enhanced Catalytic Activities of Nanostructured Materials(2014-10-31) Martinez De La Hoz, Julibeth MilenaCatalysis has enabled the development of very important industrial processes, especially those related to the petroleum and chemical industries. This has led to a significant influence in the worldwide economy, with 20% of it depending on catalysis. Current reliance of the industrial world on catalysis and rapidly increasing worldwide energy prices have motivated the search for improved catalysts allowing more energy-efficient processes. Catalysts performance is affected by the shape, structure, and chemical composition of the catalysts. Fortunately, the development of nanotechnology has allowed researchers to control the structure and morphology of catalyst nanoparticles, as well as that of solid supports. Even though, these approaches have enhanced the reactivity of materials towards specific reactions, there is still much more room for improvement. In this work, the incorporation of electron-rich environments into the structure of nanocatalysts is proposed as a new approach for the enhancement of the catalytic activity of nanomaterials. This study is conducted in its entirety using computational quantum-based simulations. The effect of electron-rich regions on activation barriers for the dissociation of diatomic molecules is studied using metallic slit-type pores, finding that electron-rich environments enhance the reactivity of nanomaterials by reducing activation barriers required for the dissociation of molecules. The influence of electronic and geometric effects in the pores is also evaluated. It is found that local geometric characteristics, such as stacking planes forming the pore, and the presence of step-like defects influence adsorption energies and barriers for dissociation of molecules. Additionally, electrons inside the metallic pores have energies close to the Fermi-energy of the metal surfaces, which may allow tuning their energies for interactions with LUMO anti-bonding orbitals of specific molecules. Subsequently, electron-rich regions are incorporated into a 3D nanostructured material (Pt22/NPG). This proposed catalyst shows enhanced reactivity towards the dissociation of gas-phase molecules. Additionally, Pt22/NPG may display enhanced reactivity, even when electron-rich regions do not interact with the molecules of interest, due to the good dispersion of Pt-clusters. Therefore, the incorporation of electron-rich environments into nanocatalysts is shown to be an efficient approach for the enhancement of the catalytic activity of nanomaterials.Item Heterogeneity of polymers: diluents nanoconfined in rubber networks and mechanical hole burning spectroscopy(Texas Tech University, 2008-12) Qin, Qian; McKenna, Gregory B.; Quitevis, Edward L.; Vaughn, Mark W.; Khare, RajeshHeterogeneity at micrometer or nanometer scale is of great importance and has drawn considerable attention in recent years. Many physical properties of materials, such as dynamic relaxation, diffusion or transport phenomenon can be affected and explained by the heterogeneous nature. The present dissertation focuses on the heterogeneity of polymers and consists of two parts of projects. The first part of dissertation studies the nanoscale heterogeneity and structure in rubber networks. Thermoporosimetry is applied to characterize the network heterogeneity, which extends the Gibbs-Thomson model concerning the relationship between the melting point depression and the crystal size and requires the quantitative agreement between the Flory-Huggins theory and the melting points of the diluents in the uncrosslinked rubber. This dissertation presents the first systematic investigation on the validity of the Flory-Huggins theory in terms of melting point depression of diluents mixing with polymers. The correct use of thermoporosimetry to obtain the nanoheterogeneity of rubber networks and its calibration by controlled porous glasses are discussed and addressed. The second part of dissertation focuses on the characterization of dynamic heterogeneity of polymers by means of a novel rheological method called Mechanical Spectral Hole Burning (MSHB). The MSHB on a triblock copolymer in the vicinity of its order-disorder transition is investigated. By successfully distinguishing the heterogeneity from homogeneity as well as different heterogeneity degrees, MSHB promises to be a potentially powerful tool to probe dynamic heterogeneity for polymeric materials. Additionally, the MSHB is further investigated on a series of polystyrene/ diethyl phthalate solutions. The effect of different types of heterogeneity such as entanglement length, entanglement density and chain end density is explored and different types of dynamics are examined by the MSHB. The results are consistent with a heterogeneous dynamics over the time scales from close to Rouse regime into the rubbery plateau regime and for the rubbery plateau-to-terminal flow transition regime. Terminal relaxation dynamics, on the other hand, is found to be homogeneous for the PS/diethyl phthalate solutions investigated.Item Influence of Confinement Housing on the Cecal Environment of the Horse(2012-02-14) Wolford, AshleyEight cecally cannulated Quarter Horse geldings were utilized in a crossover design with two 28 d periods with a 21 d washout period between. Horses were adapted to dietary treatments from d 1 to 19, dry matter intake was determined from d 20 to 24, and cecal fluid was collected on d 28. Horses were paired by age and body weight (BW) and randomly assigned to treatment. Treatments consisted of housing horses individually in stalls or group housed in a dry lot pen. Regardless of treatment, all horses were individually fed a pelleted concentrate at 1% BW (as fed) offered twice daily 12 h apart. All horses had ad libitum access to coastal bermudagrass hay. Hay was offered to stalled horses initially at 2% BW (as fed) then adjusted based on 120% of a previous 3 d average of voluntary intake. A dual marker system was utilized for estimation of voluntary intake in all horses using titanium dioxide (TiO2) as the external marker and acid detergent insoluble ash (ADIA) as the internal marker. Cecal samples were collected 4-h after the morning meal and immediately analyzed for pH. Samples were transported to the USDA/ARS laboratory to enumerate total anaerobic bacteria and lactic acid bacteria, and to determine methane and ammonia activity. Cecal pH was influenced by housing (P = 0.02) with group housed horses having lower cecal pH values when compared to stalled horses (6.52 +/- 0.04 and 6.69 +/- 0.04, respectively). The cecal pH values of this study are similar to other reported values when feeding similar diets (5). Populations of cecal total anaerobic bacteria and lactobacillus were not influenced by housing (P >= 0.21). Treatments did not affect the production of acetate, propionate, or butyrate (P >= 0.15). Additionally, methane and ammonia production were not affected by treatments (P >= 0.17). Forage intake was greater for group housed horses (P = 0.04) than stalled (8.47 +/- 0.89 kg DM/d and 5.17 +/- 0.89 kg DM/d, respectively). In conclusion, confinement housing did not greatly influence the cecal environment of a horse when similar diets were offered.Item Platform-level protection for interacting mobile apps(2016-08) Xu, Yuanzhong, Ph.D.; Witchel, Emmett; Alvisi, Lorenzo; Geambasu, Roxana; Pingali, Keshav; Shmatikov, VitalyIn a modern mobile platform, apps are mutually distrustful, but they share the same device and frequently interact with each other. This dissertation shows how existing platforms, like Android and iOS, often fail to support important data protection scenarios, and describes two systems to improve platform-level security. First, many data leaks in existing platforms are due to the lack of information flow control for inter-app data exchanges. For example, a document viewer that opens an attachment from an email client often further discloses the attachment to other apps or to the network. To prevent such leaks, we need strict information flow confinement, but a challenge to enforce such confinement in existing platforms is the potential disruptions to confined apps. We present Maxoid, a system that uses context-aware custom views of apps' storage state to make information flow enforcement backward compatible. Second, apps' abstraction of data has diverged from platforms' abstraction of data. Modern mobile apps heavily rely on structured data, and relational databases have become the hub for apps' internal data management. However, in existing platforms, protection mechanisms are coarse-grained and have no visibility to the structures of apps' data. In these platforms, access control is a mixture of coarse-grained mechanisms and many ad hoc user-level checks, making data protection unprincipled and error-prone. We present Earp, a new mobile platform that combines simple object-level permissions and capability relationships among objects to naturally protect structured data for mobile apps. It achieves a uniform abstraction for storing, sharing and efficiently protecting structured data, for both storage and inter-app services.Item Retrofit of deficient lap splice with post-installed anchors(2015-12) Beiter, Katelyn Sean; Bayrak, Oguzhan, 1969-; Hrynyk, Trevor DAs concrete infrastructure ages or is re-purposed, there is an increasing need for efficient retrofit solutions, with deficient lap splices being one of many research areas. A possible method to increase the capacity of deficient lap splices is to use post-installed undercut anchors. These anchors function as active confinement in the splice region, potentially allowing members with inadequate lap splice lengths to reach the required design capacity. The solution presented in this thesis requires access to only one face of the reinforced concrete specimen, which could facilitate implementation on existing structures. However, limited research has been done on the use of post-installed anchors as a retrofit strategy for lap splices, and previous research on the retrofit of deficient lap splices has focused primarily on the use of either carbon fiber or metal jackets. To evaluate the capabilities of this retrofit solution, four large-scale tests on beam specimens have been completed at The University of Texas at Austin. The first specimen tested contained the full lap splice length as required by ACI 318-71 provisions, while in the other three, only half of that lap splice length was provided. The specimen with the full lap splice length was tested as a control specimen and one of the specimens with half the lap splice length was tested without a retrofit to determine baseline behavior. These tests formed the basis to evaluate the effectiveness of the retrofit techniques implemented on the other two specimens. Results from these tests indicated that post-installed anchors could enhance both the strength and ductility of members with deficient lap splices, but the enhanced members demonstrated limited ductility.Item The glass transition in confined and heterogeneous systems(Texas Tech University, 2008-08) Zheng, Wei; Simon, Sindee L.; Quitevis, Edward L.; Weeks, Brandon L.; McKenna, Gregory B.The glass transition (Tg) is an interesting but challenging problem. Although this phenomenon has been studied for over half a century, Tg is still not well understood especially at the molecular level. One important feature which seems to be missing in the current understanding is its inherent heterogeneous dynamics. The aim of this work is to study the Tg behavior under various conditions such as for material freeze-dried from dilute solutions, confined in nanopores, and blended with other components, and to examine the relation between the dynamic heterogeneity and the observed Tg behavior. Freeze-dried materials from dilute solutions show different Tg behavior from the bulk; however, the origin of the difference remains unclear. In this work, the residual solvent effect on the calorimetric Tg of freeze-dried polystyrene is investigated. A linear correlation is found between the Tg depression and the residual solvent concentration, in agreement with data in the literature, indicating that the Tg depression observed for polymers freeze dried from dilute solution is due to residual solvent. Confinement at the nanoscale is also found to affect the glass transition behavior. Two hydrogen-bonded liquids, glycerol and propylene glychol, confined in silanized and unsilanized nanopores are studied to elucidate the confinement effects on Tg. Upon confinement, these two materials show similar behavior except that an additional Tg is observed for propylene glycol. We find that the confinement effects strongly depend on the competition between size effects and surface effects. Recently, a self-concentration model was proposed to predict the segmental dynamics of misicible polymer blends. To test this model, in this work, the dynamic properties of athermal blends of poly(á-methyl styrene) with its oligomer is examined. The effective Tgs of the components determined from the calorimetric transition can be described by the self-concentration model. However, the self-concentration value obtained is much lower than the theoretical prediction, indicating weak chain connectivity effects in the athermal mixture. Moreover, compared to the pure materials, the blends exhibit considerably broadened transitions and depressed enthalpy overshoots, presumably resulting from their broader relaxation time distribution. In addition to studies dealing with confined or heterogeneous systems, calorimetric measurements of Tg and the limiting fictive temperature, Tf', as a function of cooling and heating rates are performed for a polystyrene to examine the relationship between the Tg and Tf' and to examine the conversion dependence of the apparent activation energy.