Zirconium tungstate (ZrW2O8) is a ceramic that shows large isotropic negative thermal expansion over a wide range of temperature. This unique property makes it an interesting candidate for applications where thermal expansion mismatch between components constitutes a problem. ZrW2O8 is typically produced by solid-state reaction between zirconium oxide and tungsten oxide at 1200oC. In some studies, ZrW2O8 precursors have been produced from relatively expensive zirconium and tungsten sources. While the origin of negative thermal expansion has been the main focus in the majority of publications, production of particles with controlled size, distribution and morphology has not been studied extensively. Electrospinning is a simple technique for producing micron/nano sized fibers from polymer solutions. The method can also be used for producing ceramic or polymer/ceramic composite fibers by electrospinning of a mixture of ceramic precursors or ceramic nanoparticles with suitable polymers. Ceramic precursors could be synthesized either by sol-gel or chemical precipitation routes before mixing them with polymer solutions and a final burnout step would be needed, in case the fiber is desired to be composed of the ceramic phase. Electrospinning technique has not been employed to the production of ZrW2O8 ceramic fibers. In this study a novel precursor for ZrW2O8 from relatively cheaper and abundant starting chemicals, namely zirconium acetate and tungstic acid were used. Experimental details of development of the precursor are presented with a discussion on the effects of solution parameters on the phase purity of the fired product. Besides the solution parameters investigated (i.e. solubility of tungstic acid, adjustment of the stoichiometry, final pH of the solution, ageing time), evolution of the heat treatment protocol was used in the production of phase pure ZrW2O8. Second, the suitability of the developed precursor for producing ZrW2O8 in fiber form was investigated. Preliminary studies involved the adjustment of the viscosity of precursor solution for electrospinning with poly (vinyl alcohol) (PVA). Optimum PVA concentration leading to bead-free nanofiber mats and a method to increase the fiber production rate were reported. The characterization of the products was achieved by SEM and XRD.

This study aims synthesis of metal/polymer one dimensional nanostructures by micelle formation, reduction, and electrospinning route, and to analyze the morphological characteristics of composite nanofibers. The study was carried out in three main steps. First, the reverse micelle structures were established between the anionic surfactant and the metal ion. The surfactant acts as an agent to bind metal ions together so that the arrangements of metal ions can be controlled in the solution. As the surfactant concentration increases, reverse micelles grow and reverse wormlike micelle structures are observed. Wormlike micelles are elongated semi flexible aggregates which form a spherocylinder form repeating units. Metal ions are in the core and surrounded with the surfactant. The polymer attached to the wormlike structure acts as a shield and prevents phase separation in a hydrophilic medium. Different polymer and surfactant concentrations were tried to determine the optimum polymer and surfactant concentrations for reverse micelle formation. The size analyses of the reverse micelle structures were done by dynamic light scattering technique. In the second step, metal ions in the micelles were reduced by using hydrazine hydrate to obtain metal cores in the center of wormlike micelles. Finally, electrospinning was carried at room temperature and in air atmosphere. The characterization of nano composites was done by Scanning Electron Microscopy. It was found that the size of the reverse micelle structures affects the distribution of metal nano partices in polymer nano fibers. In order to distribute the metal nano particles homogeneously, the optimum size of reverse wormlike micelles was found to be between 420 and 450 nm.

Cellulose nanowhiskers reinforced poly(vinyl alcohol)(PVA) nanofiber web is successfully fabricated using electrospinning technique and the mechanical properties of the single electrospun fiber are measured using nanoindentation method. The morphology and mechanical properties of highly aligned electrospun fiber webs are investigated. It is found that the modulus and tensile strength of aligned webs are higher than those of isotropic electrospun fiber webs. Experimental results are compared with a longitudinal Halpin-Tsai model. Ice-templated(IT) cellulose microfibril porous foams are successfully fabricated via unidirectional freezing methods. The morphology and growth mechanism of IT surfaces are investigated successfully using cellulose microfibrils and hydrophillic substrates. By controlling the temperature gradient between cellulose microfibril suspensions and secondary freezing mediums, various surface structures including honey-comb like structures, ellipse-shape channel strcutures, fully developed multichannel structures are obtained. For the honey-comb like patterned surface, high contact angles are observed. On the other hand, for the layered patterned surface, anisotropic wetting properties are observed.

Fullerene research has advanced to elevated levels in a short period of time due to the unique chemical and physical properties of the caged molecule that have been utilized in numerous applications. Due to the spherical shape of the fullerene molecule which allows for a hollow cavity, encapsulation of atoms or small molecules can occur within the ball structure. This encapsulation creates an endohedral component that is limited from interacting with other molecules which creates potential of control over electronic information of the isolated molecule. Endohedral fullerenes have the potential as serving as the base unit in a quantum computer if control over global alignment is attained. Thus, by using the inherent self-assembling capabilities of some organic materials, ordered endohedral fullerenes can be achieved. This dissertation investigates the ability to use self-assembling strategies to obtain alignment which include ordering within a morphologically controlled copolymer matrix, forming a supramolecular polymer complex with cyclodextrin, and encapsulation within the helical wrap of polymer chains. The ultimate goal is to understand the dynamics that control association and orientation of varying fullerene-based molecules in each strategy in order to maximize control over the final alignment of endohedral elements.

Thesis (M.S.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed Jan. 29, 2010). Includes bibliographical references (p. 66-70).

This dissertation has aimed to fabricate polypeptide based biomaterial and characterize physical properties. Electrospinning is used as a tool for the sample fabrication. Project focused on determining the feasibility of electrospinning of certain synthetic polypeptides and certain elastin-like peptides from aqueous feedstocks and to characterize physical properties of polymer aqueous solution, cast film and spun fibers and fiber mats. The research involves peptide design, polymer electrospinning, fibers crosslinking, determining the extent of crosslinking, fibers protease degradation study, fibers stability and self-organization analysis, structure and composition determination by various spectroscopy and microscopy techniques and characterization of mechanical properties of individual suspended fibers. Fiber mats of a synthetic cationic polypeptide poly(L-ornithine) (PLO) and an anionic co-polypeptide of L-glutamic acid and L-tyrosine (PLEY) of defined composition have been produced by electrospinning. Fibers were obtained from polymer aqueous solution at concentrations of 20-45% (w/v) in PLO and at concentrations of 20-60% (w/v) in PLEY. Applied voltage and spinneret-collector distance were also found to influence polymer spinnability and fibers morphology. Oriented fibers were obtained by parallel electrodes geometry. Fiber diameter and morphology was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). PLO fibers exposed on glutaraldehyde (GTA) vapor rendered fiber mats water-insoluble. A common chemical reagent, carbodiimide was used to crosslink PLEY fibers. Fiber solubility in aqueous solution varied as a function of crosslinking time and crosslinker concentration. Crosslink density has been quantified by a visible-wavelength dye-based method. Degradation of crosslinked fibers by different proteases has been demonstrated. Investigation of crosslinked PLEY fibers has provided insight into the mechanisms of stability at different pH values. Variations in fiber morphology, elemental composition and stability have been studied by microscopy and energy-dispersive X-ray spectroscopy (EDX), following the treatment of samples at different pH values in the 2-12 range. Fiber stability has been interpreted with reference to the pH dependence of the UV absorbance and fluorescence of PLEY chains in solution. The data show that fiber stability is crucially dependent on the extent of side chain ionization, even after crosslinking. Self-organization kinetics of electrospun PLO and PLEY fibers during solvent annealing has been studied. After being crosslinked in situ, fibers were annealed in water at 22 °C. Analysis by Fourier transform infrared spectroscopy (FTIR) has revealed that annealing involved fiber restructuring with an overall time constant of 29 min for PLO and 63 min for PLEY, and that changes in the distribution of polymer conformations occurred during the first 13 min of annealing. There was a substantial decrease in the amount of Na+ bound to PLEY fibers during annealing. Kinetic modeling has indicated that two parallel pathways better account for the annealing trajectory than a single pathway with multiple transition states. Bacteria have been engineered to make novel 250-mer elastin-like polypeptides (ELPs). Each was predicted to have an absolute net charge of less than 0.05 electron charges per amino acid residue in aqueous solution at neutral pH. Polymer structure in solution has been assessed by Circular dichroism spectroscopy (CD) and dynamic light scattering (DLS). Suitability for materials manufacture has been tested by electrospinning. Here, we have also tested the hypothesis that blending polypeptides of radically different amino acid composition will enable the realization of novel and potentially advantageous material properties. Aqueous polymer feedstock solutions consisted of pure ELP or ELP blended with a synthetic polypeptide, PLEY, which is highly ionized at neutral pH and spinnable. Morphology analysis of blended fibers by SEM has revealed the formation of a surprising variety of structures that are not seen in fibers of ELP or PLEY alone, for example, hollow beads. Analysis of blended fibers by fluorescence microscopy showed that there was little or no phase separation, despite the large difference in electrical properties between ELP and the synthetic polymers. Structure and composition of PLO, PLEY, ELPs and blends and electrospun fibers made of these polymers have been determined and compared. CD and FTIR have been utilized to obtain structural information on these polymers in aqueous solution, cast films and fibers. Fiber composition has been analyzed by EDX. Protein adsorption has been analyzed by quantitative fluorescence microscopy. The polymers adopted random coil-like conformations in aqueous feedstocks at neutral pH and in dehydrated cast films and fibers on glass, and the fibers comprised numerous counterions, according to spectral analysis. Adsorption of model proteins and serum proteins onto hydrated and crosslinked fibers depended on the electrical charge of the proteins and the fibers. The surface charge density of the fibers will be comparable to, but less than, the charge density on the outer leaflet of the plasma membrane of usual eukaryotic cells. Mechanical properties of a series of as-spun and crosslinked PLO and PLEY nanofibers with various diameters have been analyzed by using the pure bending mode and AFM technique. Aligned nanofibers were deposited on top of a microsized groove etched on a glass substrate. AFM tip was used as a probe, which could apply a measurable deflection and force onto the suspended nanofiber at a force calibration mode, so that the Young's modulus of a single nanofiber can be calculated based on the basic beam bending theories. The Young's moduli of the studied peptide nanofibers increased significantly with decreased fiber diameters. This study has also demonstrated that crosslinked electrospun PLO and PLEY fibers have a higher Young's modulus compared with their as-spun counterparts. Taken together, the results will advance the rational design of polypeptides for peptide-based materials, especially materials prepared by electrospinning. It is believed that this research will increase basic knowledge of polymer electrospinning and advance the development of electrospun materials, especially in medicine and biotechnology. The study has yielded two advances on previous work in the area: avoidance of an animal source of peptides and avoidance of inorganic solvent. The present results thus advance the growing field of peptide-based materials. Non-woven electrospun fiber mats made of polypeptides are increasingly considered attractive for basic research and technology development in biotechnology, medicine and other areas.

Polyamide 6 (PA6) was melt-blended with an intumescent flame retardant (FR) and nanoparticles (multi-wall carbon nanotubes [MWNTs] and nanoclays) to produce multi-component FR-PA6 nanocomposites. Thermal, flammability properties, char residue morphology, and mechanical properties of FR-PA6 nanocomposites were characterized. The flame retardant properties were enhanced according to UL 94 and microscale combustion calorimeter (MCC) measurements, whereas the thermal stability was decreased. Mechanical properties of the bulk material, especially elongation at break, were severely reduced, with the exception of tensile modulus which increased significantly. FR-PA6 nanofibers were processed via electrospinning. Electrospinnability, morphology of the nanofibers, combustion, and thermal properties were also analyzed. As for the bulk-form nanocomposite, improved combustion properties of these nanofibers were successfully achieved though thermal stability was compromised. With proper FR additive, the synergism between MWNTs and nanoclays was observed in PA6 resin. / text

The objective of this research is to develop a new class of miniaturized sensors on-catheter technology through the integration of functional nanomaterials and flexible microsystems, with high sensitivity, fast recovery time, reduced form factor, for in situ blood pressure and flow monitoring with minimal invasiveness. Real-time endovascular pressure measurement techniques are crucial to evaluate the hemodynamics, which indicates the physiological state of the cardiovascular system. Current technology relies on fluid filled catheter coupled to remote transducers to measure endovascular pressures and gradients. The fluid filled catheters are bulky, inherently inaccurate due to the tubing mechanical resonance, and with low signal integrity due to the vibration noises from the environment. Silicon based conventional pressure sensors have complications due to issues of catheter stiffness, biocompatibility or small form factor integration. We propose a paradigm shift in designing the endovascular pressure sensing technology, through developing compact flexible sensing structures using nanoengineered piezoelectric polymers which can be integrated on catheters without consuming the internal lumen space. We focused on designing novel nanostructures using PVDF-TrFE (Polyvinyledene fluoride trifluoroethylene), with well controlled [Beta]-crystalline phase to significantly improve the resulting sensor performance. The research objectives include: (1) Thin-film structures for higher piezoelectric effect without any mechanical stretching or poling requirements, (2) High density highly-aligned electrospun nanofibers through electrospinning towards enhanced sensitivity; (3) Core-shell electrospun nanofiber for tapping the near [Beta]-crystalline phase formation and high cyrstallinity by virtue of inherent stress and stretching involved in the fabrication procedure. For pressure sensor design and characterization, we worked on two main form factors designs: thin-film, and aligned electrospun nanofiber based sensors patterned on catheter tips which are ready to be deployed in intra-vascular environment. Testing results showed promising results from PVDF based pressure sensors. The average sensitivity of the PVDF sensors was found to be four times higher than commercial pressure sensor while the PVDF sensor had five fold shorter response time than commercial pressure sensor, making the PVDF sensors highly suitable for real-time pressure measurements using catheters. / text

Electrospun, non-woven, fibers have high surface area compared to conventional cast films. The thesis reports on the modification of electrospun fibers to concentrate and/or detect biohazards. In one study, electrospun fibers with affinity for the lectins ricin/concanavalin A were fabricated using molecular imprinting or through binding to immobilized antibodies, aptamers or lectin specific sugars. Attempts to fabricate imprinted electrospun fibers through inclusion of the template during the spinning process proved unsuccessful. However, electrospun fibers with affinity towards biohazards were successfully produced by post-modification with antibodies, aptamers or lectin specific saccharides. With regards to the latter, dextran, mannose and chitosan were immobilized onto nylon electrospun fibers that were partially hydrolyzed or treated with cyanuric chloride. The sugar-modified fibers bound significantly higher amount of lectins. Electrospun fibers were also fabricated, post modified with antibodies to capture and detect Salmonella. The study has illustrated the utility of electrospun fibers for biohazard diagnostics. / The National Center for Food Protection and Defense. USA

The primary objective of my thesis was to investigate the effect of crimp-like fibrous scaffolds on bovine fibroblasts and to develop a scaffold for anterior cruciate ligament (ACL) tissue engineering. To achieve this objective, fibrous biodegradable polymeric scaffolds were fabricated, which upon relaxation developed a crimp-like structure, which resembled the crimp seen in native collagen. The understanding of the crimp mechanism allowed for controlling crimp-like patterns in various polymer fibre systems, and was determined to be due to residual stress coupled with an operating temperature (Top) above the glass transition temperature of the polymer (Tg). The benefit of crimp was evaluated by seeding fibroblasts on crimp-like fibres that were subjected to dynamic mechanical loading. The results showed a significant increase in extracellular matrix (ECM) accumulation by fibroblasts that experienced crimp unfolding. In addition, fibroblasts seeded on mechanically stimulated crimp-like fibrous scaffolds formed ECM bundles that resembled collagen fibre fascicles. Two separate studies were conducted to fabricate fibrous scaffolds with high modulus: one on thermoplastic polyesters and the other on a photocrosslinkable polyester. Of the thermoplastic polyesters investigated, poly(L-lactide-co-D,L-lactide) P(LLA-DLLA) exhibited the highest modulus, and was the most resistant to hydrolytic degradation. These fibres were placed in a heated aqueous environment to exhibit a crimp-like pattern similar to that of native collagen. Bovine fibroblasts were shown to attach, proliferate and deposit ECM on the surface of the P(LLA-DLLA) fibrous scaffolds. In addition, the deposited ECM appeared to be organized in distinctive bundles that resembled fascicles found in native ACL. However, upon crimp unfolding the crimp was not completely recovered. Photocrosslinkable poly(L-lactide-co-trimethylene carbonate cinnamate) P(LLA-TMC cinnamate) fibres in addition to supporting cell proliferation and ECM accumulation, completely recovered their crimp-like pattern, via [2 + 2] cycloaddition of the cinnamate groups. The recovery of crimp upon unfolding is a novel design feature incorporated into electrospun fibres as it innately mimics the function of collagen fibres found in the ACL. From the results obtained it is evident that crimp and its unfolding are key design features/conditioning techniques that need to be incorporated into fibrous scaffolds that possess high modulus, intended for ligament tissue engineering. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-01-05 14:11:25.965