Thesis (M.S.M.E.)--University of Delaware, 2005. / Principal faculty advisor: Ajay K. Prasad, Dept. of Mechanical Engineering. Includes bibliographical references.

The research work presented in this thesis comprises a detailed investigation of conductivity mechanism in crystalline polymer electrolytes and development of a new class of ceramic-polymer composite electrolytes for Li-ion batteries. Firstly, a robust methodology for the synthesis of monodispersed poly(ethylene oxides) has been established and a series of dimethyl-protected homologues with 13, 15, 17, 28, 29, 30 ethylene oxide repeat units was prepared. The approach is based on reiterative cycles of chain extension and deprotection, followed by end-capping of the oligomeric chain ends with methyl groups. The poly(ethylene oxide) homologues show a superior level of monodispersity to previous work and were subsequently used to prepare crystalline PEO6:LiPF6 polymer electrolytes. A correlation between the number of ether oxygens in the polymer chain and the ionic conductivity of crystalline polymer electrolytes has been established. The structure and dynamics of the monodispersed complexes were studied using solid-state NMR spectroscopy for the first time. The results are in agreement with the proposed mechanism of ionic conductivity in crystalline polymer electrolytes. A new class of composite solid electrolytes for all-solid-state batteries with a lithium metal anode is reported. The composite material consists of a 3D interpenetrating network of a ceramic electrolyte, Li₁.₄Al₀.₄Ge₁.₆(PO₄)₃, and an inert polymer (polypropylene), providing continuous pathways for the ionic transport and excellent mechanical properties. 3D connectivity of this novel composite was confirmed using X-ray microtomography and AC impedance spectroscopy.

Les dendrimères et polymères contenant des métaux de transition comme le fer, lecobalt et le rhodium peuvent servir à la fabrication des nanomatériaux utiles à lacatalyse, la reconnaissance moléculaire et l’électronique moléculaire. Pour leurconstruction, des liaisons ioniques, de la chimie click : CuAAC et hydroamination, lapolymérisation ROMP et la polymérisation radicalaire ont été utilisés et ont permis laformation de nouveaux types de polyélectrolytes metallocéniques. La synthèse denouvelles nanoparticules d’or, d’argent et de palladium à partir de cesmétallopolymères et métallodendrimères ont été mises au point, conduisant à desréseaux à architecture spécifique bien définie. Ces assemblages supramoléculaireset ingénierie moléculaire ouvrent la voie vers l’application de la chimieorganométallique dans la conception de nouveaux nanomatériaux nanoparticulairesstructurés à l’aide des propriétés rédox des métallomacromolécules. / Dendrimers and polymers containing transition metals such as iron, cobalt andrhodium can serve in the fabrication of useful nanomaterials for catalysis, molecularrecognition and molecular electronics. For their construction, ionic bonds, clickchemistry: CuAAC and hydroamination, ROMP and radical polymerization were usedand allowed the formation of new types of metallocenyl polyélectrolytes. Thesynthesis of new gold, silver and palladium nanoparticles from these metallopolymersand metallodendrimers has been developed, leading to specific and well-definedarchitectures. These supramolecular assemblies and molecular engineering opensthe way towards the application of organometallic chemistry in the design of newstructured nanoparticle-containing nanomaterials using the redox properties ofmetallomacromolecules.

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Two-photon absorption and upconverted fluorescence has been utilized in a variety of applications in pure science and engineering. Multiphoton-based techniques were used in this research in order to understand photophysical and chemical characteristics of several fluorescent dyes and to demonstrate some of their key applications. Two-photon fluorescence microscopy (2PFM) has become a powerful technique in bio-photonics for non-invasive imaging in the near-infrared (NIR) region (700~1000 nm) that often results in less photobleaching. In Chapter 1, there is a brief introduction to fluorescence, examples of fluorescence materials, and a discussion of the advantages of two-photon absorption. 2PFM imaging was utilized in Chapters 2 to 4 for various applications. In Chapter 2, a new squaraine dye is introduced and its linear and nonlinear photophysical properties are characterized. This compound has very high two-photon absorption (2PA) cross sections and high photostability both in an organic solvent and when encapsulated in micelles. Based on these properties, this dye was demonstrated as a near-infrared (NIR) probe in in vitro 2PFM imaging with excitation over 800 nm wavelength. In Chapter 3, new profluorescent nitroxides are introduced. Nitroxide radicals are utilized for electron paramagnetic resonance (EPR) spectroscopy and in biological systems as some are known, in some manner, to mimic the behavior of superoxide dismutase (SOD) that detoxifies or mitigates oxidative stress by trapping free radicals. Here, two profluorescent nitroxides investigated for use as a two-photon fluorescent oxidative stress indicator in in vitro two-photon fluorescence microscopy (2PFM) imaging. In Chapter 4, two-photon excited (2PE) fluorescence of a conjugated polyelectrolyte (CPE), PPESO3, was studied in methanol and in water. The results of CPE quenching studies were comparable under both one-photon excitation conditions and two-photon excitation. CPE coated silica nanoparticles were incubated in HeLa cells and 2PFM imaging was demonstrated for this new class of fluorescent probe. Supramolecular structures based on organized assemblies/aggregation of chromophores have attracted widespread interest as molecular devices with potential applications in molecular electronics, artificial light harvesting, and pharmacology. In Chapter 5, J-aggregate formation was investigated for two porphyrin-based dyes, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS, 4) and an amino tris-sulfonate analog (5) in water via UV-vis, fluorescence, and lifetime decay studies. The effect of aggregation on two-photon absorption properties was also investigated. A functionalized norbornene-based homopolymer, synthesized by the ring opening metathesis polymerization technique was used as a J-aggregation enhancement template and had a role of polymer-templating to facilitate porphyrin aggregation and modulate 2PA. In Chapter 6, squaraine dye aggregates templated with single wall carbon nanotubes (SWCNTs) that were atomically clean were studied by using optical absorption spectroscopy, atomic force microscopy (AFM), and photoconductivity measurements. SWCNTs selectively promote the formation of squaraine dye aggregates with a head-to-head stacking arrangement, and these dye aggregates effectively photosensitize SWCNTs, demonstrating that this novel approach can yield highly photosensitized devices.

<p> Cationic polyelectrolytes have attracted growing attention in the field of non-viral oligonucleotides (ONs) deliveries because of their ability to bind ONs by electrostatic interactions for efficient cellular uptake. However the formation of electrostatic polymer/ONs complexes and their biological effects are still poorly understood. The relationships between polymer structure and complexation performance have not been well established. The objectives of this research are to synthesize and characterize well-defined and well-controlled cationic polyelectrolytes and to evaluate the effects of polyelectrolyte chain properties on ONs complexation. Poly(2-(dimethylamino) ethyl methacrylate) (polyDMAEMA) and its derivatives are used as the polymer candidate. A fluorescein-labeled oligonucleotide, 5 '-FGCGGAGCGTGGCAGG-3' (F: fluorescein), is used as the oligonucleotide candidate.</p> <p> Low-molecular-weight cationic polyDMAEMA samples having narrow molecular weight distribution were synthesized by living anionic polymerization (LAP) and atom transfer radical polymerization (ATRP) methods. Fully charged polyDMAEMA quats were prepared by sequential quaternization of polyDMAEMA samples, as well as by direct ATRP of the quaternized DMAEMA monomer. An aqueous GPC calibration method was first developed for the characterization of these cationic polyelectrolytes. It was found that the type of counter-ion has little effect on the hydrodynamic volume of polyDMAEMA quat. Therefore the dimethyl sulfate salt of polyDMAEMA provided a reliable calibration standard for other types of quaternized DMAEMA homopolymers.</p> <p> Cationic block copolymers of polyDMAEMA with 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol (PEG) were also prepared by ATRP. It was found that the order of monomer addition, solvent type, temperature, and molecular weight of macroinitiator have significant effects on the living feature of the polymerization. Well-controlled block copolymers were obtained when polyHEMA was used as the macro initiator.</p> <p> The complexation capability of the prepared polyelectrolytes with oligonucleotides (15 mer) was evaluated by a fluorescence technique. It was found that the complexation performance depends on polymer molecular weight, charge density, and counter-ion type, as well as polymer concentration and block composition. The polymer sample that has double molecular weight of the ONs gave the optimal complexation performance.</p> / Thesis / Master of Applied Science (MASc)

In this thesis, we use the self-consistent field theory (SCFT) to study neutral and charged block copolymer melts and blends in thin films and bulk. We showcase the utility of the SCFT by applying it to a number of different model systems. In our first study, we examined the elastic properties of multi-component bilayer membranes composed of amphiphilic AB/ED diblock copolymers. We focused on the effects of chain architecture and interactions between the amphiphilic molecules on the line tension or edge energy of a membrane pore. We discovered a direct relationship between the effective volume of the amphiphilic molecules, which is dictated by their architecture, and the line tension. We found that the addition of cone-shaped molecules to the membrane results in a decrease in the line tension. The opposite effect is seen for inverse cone-shaped amphiphiles, where an increase in their concentration results in an increase of the line tension. Studies two and three fall under the theme of directed self assembly of block copolymer thin films. First we examined the effects of ion concentration on the strength of the external electric field required to reori- ent lamellar domains from the parallel to the perpendicular orientation. The change in the critical electric field is found to be dependent on whether the neutral or charged polymer species is favoured by the top and bottom surfaces. In the second study, we examined the mechanism of using the entropic effect to direct the self assembly of micro domains in star block copolymer thin films. We control the architecture of star block copolymers by varying the number of arms, ranging from a linear chain with 1-arm to 4-arm star block copolymers. Using both experiments and SCFT, we showed that the entropic effect is enhanced in star block copolymer blends with greater number of arms. Furthermore, we showed that the entropic effect can be used to direct the self assembly of micro domains perpendicular to the substrate. In our last study, we examined the unbinding transition of the α-BN phase in pentablock terpolymer/ homopolymer blends. We constructed a phase diagram of the system as a function of homopolymer con- centration. We discovered that the unbinding transition is preempted by the macrophase separation of the blends into block copolymer rich/ homopolymer rich domains. The results presented in this thesis help advance our understanding of various properties of polymeric systems, such as the elastic properties of multi-component membranes, directed self assembly in block copolymer thin films and the phase behaviour of block copolymers in bulk. / Thesis / Doctor of Philosophy (PhD)

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