In this work, we created shear thinning block copolymers that could be potentially utilized as an artificial vitreous replacement. The materials were created using poly(ethylene glycol) (PEG) and silicone polymers, respectively, due to their high biocompatibility. Both the ABA and BAB geometry triblock copolymers were created and were characterized using parallel plate and cone-and plate rheometers. It was observed that the materials from both geometries exhibited a decrease in viscosity with increasing shear rates, thus fulfilling the criteria of being a shear thinning material. The materials were also characterized under different aqueous conditions. It was observed that the materials with a higher PEG composition were better able to retain their physical structure – did not disperse into aqueous solutions – at higher water content levels. The materials that retained their structure were also shown to retain their shear thinning properties. In the absence of solvent, the opacity of the materials increased with increasing PEG composition ratio per copolymer chain. When exposed to different aqueous conditions, the opacity of the materials was found to decrease at specific water concentrations. Materials with larger PEG blocks required a greater water content to exhibit optimal light transmission. / Thesis / Master of Science (MSc)

Nitrile containing siloxane block copolymers were developed as stabilizers for siloxane magnetic fluids. The siloxane magnetic fluids have been recently proposed as internal tamponades for retinal detachment surgery. PDMS-b-PCPMS-b-PDMSs (PDMS = polydimethylsiloxane, PCPMS = poly(3-cyanopropylmethylsiloxane) were successfully prepared through kinetically controlled polymerization of hexamethylcyclotrisiloxane initiated by lithium silanolate endcapped PCPMS macroinitiators. The macroinitiators were prepared by equilibrating mixtures of 3- cyanopropylmethylcyclosiloxanes (DxCN) and dilithium diphenylsilanediolate (DLDPS). DxCNs were synthesized by hydrolysis of 3-cyanopropylmethyldichlorosilane, followed by cyclization and equilibration of the resultant hydrolysates. DLDPS was prepared by deprotonation of diphenylsilanediol with diphenylmethyllithium. It was found that mixtures of DxCN and DLDPS could be equilibrated at 100°C within 5-10 hours. By controlling the DxCN-to-DLDPS ratio, macroinitiators of different molecular weights could be obtained. The major cyclics in the macroinitiator equilibrate are tetramer (8.6 ± 0.7 wt%), pentamer (6.3 ± 0.8 wt%) and hexamer (2.1 ± 0.5 wt%). 2.5k-2.5k-2.5k, 4k-4k-4k, and 8k-8k-8k triblock copolymers were prepared and characterized. These triblock copolymers are transparent, microphase separated and highly viscous liquids. It was found that these triblock copolymers can stabilize nanometer gamma-Fe₂O₃ and cobalt particles in octamethylcyclotetrasiloxane or hexane. Hence PDMS-b-PCPMS -b-PDMSs represent a class of promising steric stabilizers for silicone magnetic fluids. / Master of Science

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

No description available.

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.

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

Thesis (M.S.)--University of Florida, 2006. / Title from title page of source document. Document formatted into pages; contains 61 pages. Includes vita. Includes bibliographical references.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy