Block copolymers have been subject of tremendous research interest owing to their capability of undergoing self-assembly which allows them to tailor their electrical, optical, and mechanical properties. Statistical mechanics of flexible block copolymers is well understood. However, there are many unresolved issues with confinement of block copolymers as well as structure formation in block copolymers having non-flexible polymer blocks. We develop mean field theory models to address the issues arising in thermodynamics of such complex block copolymers. Also, we develop theoretical formalisms to understand the link between morphology and macroscopic properties in these block copolymers. We study the stability and ordering in thin films of flexible diblock copolymer in the presence of compressible solvent using a combined polymer mean field theory and lattice gas model for binary fluid mixtures. We utilize mean field theory model to understand the self-assembly behavior in side-chain liquid crystalline block copolymers which involve interplay between microphase separation and liquid crystalline ordering of side chain mesogenic units. We extend the field theoretic models for block copolymer to account for self-assembly in semicrystalline block copolymers. The semicrystalline chain is modeled as a semiflexible chain having non-bonded attractions between parallel bonds. We characterize the structure formation in such block copolymers as a function of the rigidity of the semicrystalline chain. Then we extend the formalism to study semicrystalline triblock and pentablock copolymers and evaluate bridging fractions in different sequences of semicrystalline multiblock copolymers. Rod-coil block copolymers have a flexible polymer covalently linked to rigid polymer. Such polymers have potential applications as organic LEDs and photovoltaic devices. We study the self-assembly of such block copolymer under confinement. To make these block copolymers viable as photovoltaic devices, we performed the photovoltaic modeling of devices based on self-assembly of block copolymers. We characterize the interplay between self-assembly and anisotropy of charge transport (arising due to rigid polymer chains) in determining the eventual photovoltaic properties. / text

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One of the amazing properties of human vision is its ability to feel the depth of the scenes being viewed. This is made possible by a process named stereopsis, which is the ability of our brain to fuse together the stereo image pair seen by two eyes. As a stereo image pair is a direct result of the same scene being viewed by a slightly different perspective they open up a new paradigm where spatial redundancy could be exploited for efficient transmission and storage of stereo image data. This thesis introduces three novel algorithms for stereo image compression. The first algorithm improves compression by exploiting the redundancies present in the so-called disparity field of a stereo image pair. The second algorithm uses a pioneering block coding strategy to simultaneously exploit the inter-frame and intra-frame redundancy of a stereo image pair, eliminating the need of coding the disparity field. The basic idea behind the development of the third algorithm is the efficient exploitation of redundancy in smoothly textured areas that are present in both frames, but are relatively displaced from each other due to binocular parallax. Extra compression gains of up to 20% have been achieved by the use of these techniques. The thesis also includes research work related to the improvement of the MPEG-4 video coding standard, which is the first audiovisual representation standard that understands a scene as a composition of audio-visual objects. A linear extrapolation based padding technique that makes use of the trend of pixel value variation often present near object boundaries, in padding the exterior pixels of the reference video object has been proposed. Coding gains of up to 7% have been achieved for coding boundary blocks of video objects. Finally a contour analysis based approach has been proposed for MPEG-4 video object extraction.

The adsorption and the aggregation behaviour of poly(ethylene oxide-b-propylene oxide- b-ethylene oxide) copolymers (EPE) and their mixtures with surfactants of different ionic characters: sodium dodecyl sulphate (SDS), dodecyltrimethylammonium chloride (DTAC) and tetraethylene glycol monooctyl ether (C₈E₄), have been investigated using surface tension and neutron reflection measurements. The first part of the thesis is concerned with the adsorption properties of EPE copolymers at the air-solution interface. The surface tension curves for the copolymers show two breaks similar to those published for Pluronic 3 surfactants (commercially available EPE copolymers). Earlier explanations of this behaviour are inconsistent with the neutron reflection results. The adsorption isotherms obtained by neutron reflection have two steps, one at low concentrations leading to a plateau followed by a substantial rise up to the CMC. The low-concentration breakpoint is attributed to two different effects, the depletion of copolymer molecules in the bulk of the solution and the composition polydispersity. In general, the structure of the adsorbed layer can be described in terms of four layers. The outermost layer is always water free and contains only PO units. The EO residues form tails, which extend into the solution over a distance shorter than the fully extended length. Depending on the conditions, some PO is also found in this tail region. The second part of the thesis is concerned with the effect of mixing EPE copolymers with surfactants of different ionic characters. The formation of mixed micelles and mono layer between EPE 3000-14 and ionic surfactants show a surprisingly strong attractive interaction, which is attributed to a dehydration mechanism. In the mixed micelle formation, in particular, the loss of hydration water molecules found in the micelle core of the copolymer would lead to a substantial gain in entropy. The surface compositions from neutron reflection generally disagree with the predictions of Pseudophase Separation Model. It is believed that changes of hydration upon mixing may be responsible for the deviations as it is not taken into account by the Pseudophase Separation Model. From the neutron reflection studies, DTAC appears to accumulate preferably in the uppermost part of the mixed interfacial layer, while SDS would rather stay in the aqueous phase region. In the C₈E₄/EPE 3000-14 system, the mixed micellization results in strong repulsive interaction, which is attributed to a further hydration of the copolymer micelle core by the incorporation of the solvated C₈E₄ headgroups. However at the air-solution interface, both C₈E₄ and EPE 3000-14 are found to mix ideally. The difference between mixed micelle and mono layer formation observed for such a system is believed to be associated with the structure of the two states. The orientation of the copolymer molecules in the interfacial layer is such that the contact of PO groups with water molecules is significantly reduced. C₈E₄ molecules appeared to adsorb preferentially within the uppermost part of the interfacial layer rich in PO groups.

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Simple molecular building blocks, arranged in a repeating manner with hierarchical levels of organization, may lead to emergent functional properties, which would not otherwise be exhibited by the building blocks alone. The design principles of periodicity and hierarchical order are pervasive in nature, and have been borrowed to engineer man-made materials with functionality beyond their component parts. This thesis explores the development and application of block copolymers as templates for the fabrication of functional nanostructures. The core linear diblock copolymer may be pre- or post-functionalized with elements such as semiconducting moieties, topochemical precursors, and biomolecules. Periodicity is observed in the highly-ordered packing of the small molecules and patterns resulting from the cooperative self-assembly of the block copolymers and small molecules. The collective order of periodic structures at multiple lengths scales, ranging from the nanometer to micrometer regime, leads to the fabrication of hierarchical systems. These findings contribute to the critical development of complex architectures and understanding their structure-property relationships.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Frank Steven Bates. / Sc.D.

archives@tulane.edu / Silicon-based block copolymers have gained prominence because of their inherent ability to self-assemble at the low molecular weight. By utilizing this vital factor, we synthesize poly(vinylmethylsiloxane-block-methyl methacrylate) (PVMS-b-PMMA) intending to create small characteristic features with the potential application for lithography and membrane filtration. The polymer is made by a combination of anionic synthesis of PVMS, ATRP (atom radical transfer polymerization) of PMMA, and then cojoining the end-group functionalized blocks with a “click” reaction. After synthesis, thin films (10-100 nm) were self-assembled to form structures aligned perpendicular to the substrate. The morphology was observed by atomic force microscopy, grazing incidence small-angle X-ray scattering (GISAXS), and transmission electron microscopy (TEM). Additionally, the hydrophobicity of PVMS prompted us to develop a coating on microporous membrane supports for separation of water-in-oil mixtures. The PVMS was used as an effective coating to prevent fouling while maintaining high selectivity for both water-in-toluene and water-in-decane emulsion in gravity-based filtration. Finally, cyclic block copolymers (BCPs) have garnered increased attention because of their unique structure, which differs from linear BCPs due to a lack of end groups. This feature in combination with the high segregation strength of silicon-based polymers is desirable for nanolithography. Thus, we synthesized a new class of silicon-based cyclic polymer, cyclic PVMS-b-PMMA, intending to later understand the impact of topology on phase behavior, domain spacing, and nanoconfinement in thin films. / 1 / Baraka Lwoya

This thesis presents modeling of bilinear flow in tight gas wells and its behavior on single matrix block drainage. The objectives of this research are to: simulate a tight gas well using matrix block drainage under constant production pwf and with a constant production rate; be able to predict the behavior of matrix block drainage; study the effect of natural fracture(s) near a well; examine the matrix block drainage in a natural fracture network; and to validate a matrix block drainage model with a hydraulic fracture analytical solution. Two different production scenarios, constant pwf and constant rate, are assigned to a tight gas well in matrix block drainage. Matrix block drainage has two distinct permeabilities; a low permeability matrix serves as the tight gas reservoir with a high permeability streak surrounding the matrix. A well only produces from the high permeability fracture. Models were run with different sensitivity cases toward fracture half length, xf, and fracture permeability kf,. The fracture half-length reflects on a/b aspect ratio. The analytical solution for hydraulic fracture developed by Cinco-Ley and Guppy serves as the validation of matrix block drainage. Analysis on the flow regimes which occurred for different geometries and properties are provided. The log-log diagnostic plot of pseudo-pressure drop/gas rates and the log-log plot of dimensionless pressure derivatives and dimensionless reciprocal production rates are presented. Finally, an attempt to normalize the late time and early time of all geometries and properties is presented to obtain one analytical solution.