The aim of this work is to fabricate nanostructured membranes from polysulfone-based block copolymers through self-assembly and non-solvent induced phase separation. Block copolymers containing polysulfone are novel materials for this purpose providing better mechanical and thermal stability to membranes than polystyrene-based copolymers, which have been exclusively used now. Firstly, we synthesized a triblock copolymer, poly(tert-butyl acrylate)-b-polsulfone-b-poly(tert-butyl acrylate) through polycondensation and reversible addition-fragmentation chain-transfer polymerization. The obtained membrane has a highly porous interconnected skin layer composed of elongated micelles with a flower-like arrangement, on top of the graded finger-like macrovoids. Membrane surface hydrolysis was carried out in a combination with metal complexation to obtain metal-chelated membranes. The copper-containing membrane showed improved antibacterial capability. Secondly, a poly(acrylic acid)-b-polysulfone-b-poly(acrylic acid) triblock copolymer obtained by hydrolyzing poly(tert-butyl acrylate)-b-polsulfone-b-poly(tert-butyl acrylate) formed a thin film with cylindrical poly(acrylic acid) microdomains in polysulfone matrix through thermal annealing. A phase inversion membrane was prepared from the same polymer via self-assembly and chelation-assisted non-solvent induced phase separation. The spherical micelles pre-formed in a selective solvent mixture packed into an ordered lattice in aid of metal-poly(acrylic acid) complexation. The space between micelles was filled with poly(acrylic acid)-metal complexes acting as potential water channels. The silver0 nanoparticle-decorated membrane was obtained by surface reduction, having three distinct layers with different particle sizes. Other amphiphilic copolymers containing polysulfone and water-soluble segments such as poly(ethylene glycol) and poly(N-isopropylacrylamide) were also synthesized through coupling reaction and copper0-mediated reversible-deactivation radical polymerization. Finally, phase inversion membranes were prepared from polytriazole-polysulfone random copolymers, which were obtained by “clicking” 1,2,3-triazole ring substituents bearing OH groups onto the polysulfone backbone via copperI-catalyzed azide-alkyne cycloaddition. The increased hydrophilicity of membranes imparted the higher water permeability and fouling resistance to the ultrafiltration membranes. Polytriazole-b-polysulfone-b-polytriazole triblock copolymer was synthesized by RAFT and post-polymerization click modification. Hydrogen bond-mediated self-assembly induced the formation of a nanostructured polytriazole-b-polysulfone-b-polytriazole / poly(acrylic acid)-b-polysulfone-b-poly(acrylic acid) blend membrane with a 1: 1 stoichiometric ratio of triazole and acid. String-like fused micelles with polytriazole/poly(acrylic acid) corona were present on the membrane surface, after immersion in a coagulation bath of copper2+ aqueous solution.

Detection of volatile organic compounds (VOC’s) in the environment is important for human health and wellness. Long term exposure of certain VOC’s like benzene, toluene, ethylbenzene and xylene (BTEX) has a severe effect on human health. There are techniques such as gas chromatography, photo ionization, and mass spectroscopy that are time consuming, require gas sampling and are ineffective in real time sensing in air. Acoustic wave devices such as surface acoustic wave (SAW) devices can be used for sensing BTEX compounds in both vapor and liquid phase. The quartz crystal microbalance (QCM) is a low-frequency acoustic wave device, which can be used to characterize polymer film sensing quickly and easily by studying the sorption properties of BTEX compounds in them. In this work, thin films (~ 0.5 microns) of polymer/plasticizer blends are spin-coated on a 5MHz QCM for the detection of VOC’s. A polymer/plasticizer combination of poly (ethyl methacrylate) (PEMA) and a copolymer of poly (ethyl methacrylate) and poly (methyl methacrylate) (PEMA/PMMA) with di n-butyl phthalate (DBP), di-n-butyl sebacate (DBS) and n-butyl stearate (BS) are used for the detection of benzene, toluene and ethylbenzene in vapor phase. The working apparatus consists of a stream of solvent vapor diluted with nitrogen to an arbitrary concentration passing over the QCM oscillated to its resonant frequency. The sorption data are reported at 298.15 K in terms of activity as a function of weight fraction curves and are interpreted with the Flory-Huggins ternary model. The addition of plasticizer modifies the free volume properties of the polymer, thereby increasing diffusion and sensitivity of BTEX vapors. The plasticizer composition is tailored to 17.5%, for maximum sorption with minimal viscoelastic effects. The sorption and sensitivity of BTEX are interpreted and studied in terms of plasticizer type and concentration.

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No description available.

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Diblock copolymers like poly(styrene)-block-poly(2-vinylpyridine) pave the way for controllable self-assembled monolayers of nanoparticles. Using particular polymer weights and concentration, spherical micelles of PS-b-P2VP can be constructed with a non-polar PS corona and a polar P2VP core. Various precursor salts can be loaded into the core of the micelles due to interactions with the polar core which forms as the active site for nanoparticle growth. The PS corona protects the core from the atmosphere and non-polar solvents. The micelles can then act as nanobeakers for aqueous chemistry in two ways; spontaneous reactions between precursors result in nanoparticles or the trapping of precursor salts can be oxidized or reduced using polymer removal techniques like gas plasmas. In this way, reverse micelles are a facile method of growing metal, metal oxide or dielectric nanoparticles. Process parameters, such as concentration, molecular weights, nature of solvents and type of precursor salt, offer control over the periodicity and size of the monolayer of nanoparticles. Reverse micelle templating is a potentially useful nanofabrication method for tailor-made nanoparticles for use in electrical and optical devices which is not limited to form-factor of substrates. In this thesis, obstacles are identified that hinder the utility of PS-b-P2VP templated nanoparticles in device fabrication. The polymer is insulating which is detrimental to electrical applications. Additionally, the characterization of a monolayer of polymers, thus far, is limited to structural techniques such as SEM and AFM. This thesis sheds light on the mechanism of precursor loading in the micelle core, discusses the efficiency of different polymer removal techniques and uses vibrational spectroscopy for the characterization of monolayers of polymer, loaded polymer and nanoparticles. We have tested enhanced Raman methods using AFM probes to extend the resolution of normal Raman to view monolayers of empty polymers as well. Moreover, using FeCl3-loaded polymer micelles, the control offered by PS-b-P2VP templated growth on the crystal structure of nanoparticles is laid bare. The usefulness of the technique is further divulged by using ordered gamma-Fe2O3 nanoparticles in water-splitting photoanodes where they show an increased efficiency with the inclusion of nanoparticles and their periodicity. This is just an example of devices using reverse micelle templated nanoparticles, paving the way for future applications. The flexibility of this method is further revealed by constructing self-assembled Au/SnO2 nanojunctions within the PS-b-P2VP micelle cores. This was done by exploiting the spontaneous redox reaction between HAuCl4 and SnCl2 in an aqueous environment, and so can be replicated for other metals and metal oxides like Pt, Pd, Ag, TiO2 and ZnO2. The composite nanoparticles formed exhibit a tunable size and dispersion as typically seen with PS-b-P2VP micelles and so, can be used for various applications which require metal/metal oxide junctions. / Thesis / Doctor of Philosophy (PhD)

<p> Self-consistent field theory (SCFT) is a well established theoretical framework for describing the thermodynamics of block copolymer melts and blends. Combined with numerical methods, the SCFT can give useful and accurate predictions regarding the phase behavior of polymer blends. </p> <p> We have applied SCFT to study the phase behavior of blends composed of diblock copolymers (AB) and homopolymers (C). Two cases are studied in detail. In the first case the homopolymers have a repulsive interaction to the diblock copolymers. We found an interesting feature in the phase diagram that there exists a bump of the phase boundary line when A is the majority-component. In the second case, the homopolymers have an attractive interaction to one of the blocks of the diblock copolymers. A closed-loop of microphase separation region forms for strong interactions. For both cases, we have investigated the effects of homopolymer concentration, homopolymer chain length, and monomer-monomer interactions, on the phase behavior of the system. </p> <p> We also investigated micelle formation in polymer blends. Diblock copolymers (AB) blended with homopolymers (A) can self-assemble into lamellar, cylindrical and spherical micelles. The critical micelle concentrations for different geometries are determined using self-consistent field theory. The effect of varying copolymer block asymmetry, homopolymer molecular weight and monomer-monomer interactions on micelle morphology are examined. \\Then the blends are confined between two flat surfaces, the shape of the micelles may differ from that of the bulk micelles. We study the shape variation of a. spherical micelle under confinement and its dependence on the film thickness and surface selectivity. </p> / Thesis / Doctor of Philosophy (PhD)

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No description available.

Since their discovery in 1991, carbon nanotubes, and especially single walled carbon nanotubes (SWNTs), have attracted significant attention due to their unique structural, mechanical, and electronic characteristics. Although many potential applications for carbon nanotubes have been suggested, several key obstacles currently preclude their practical commercial applications. One of these is their lack of solubility and processability. In order to address this issue, a number of covalent and non-covalent nanotube functionalization techniques have recently been reported in the literature. These methods allow for the manipulation of nanotube properties, such as their solubility, through the attachment of various chemical moieties. Although most of these methods involve covalent attachment of structures to either the ends or sidewalls of SWNTs, several examples of non- covalent functionalization have also been reported. Pyrene, with its flat and aromatic structure, has been shown to form strong pi-pi stacking interactions with the surface of SWNTs. With this in mind, we explored several methods towards SWNT solubilization with diblock copolymers through non-covalent polymer- nanotube interactions. Living free radical polymerizations (SFRP, ATRP) were employed to produce diblock copolymers with narrow polydispersity. Commercial and synthetic monomers with different functionalities could be utilized to produce polymers with varying properties. Specifically, we used polymers such as polystyrene, poly(methyl methacrylate), poly(t-butyl acrylate) and poly(acrylic acid) as one block of our diblock copolymers. The second block was composed of synthetic pyrene-functionalized monomers mixed with different amounts of monomers that match the composition of the first block. It was found that, upon mixing these diblock copolymers with insoluble nanotubes in various solvents, the nanotubes were partially solubilized through pi-pi stacking with the pyrene- containing blocks. / Thesis / Master of Science (MS)