1,506 research outputs found

    Theoretical model for the electrospinning nanoporous materials process

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    AbstractThis paper deals with modeling the electrospinning nanoporous materials process. The presented theoretical models offer an in-depth insight into the physical understanding of many complex phenomena and might be very useful at shedding light on the contributing factors. Many basic properties and some special properties (such as the numbers and sizes of the pores) are tunable by adjusting electrospinning parameters such as voltage, flow rate, and others. With the increase of voltage and the decrease of flow rate, ever-increasing numbers and ever-decreasing sizes of the nanoporous microspheres have appeared. Electrospun nanoporous materials which can be regarded as thousands of Helmholtz Resonators forming together will become a kind of excellent sound absorption material

    A multi-phase flow model for electrospinning process

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    An electrospinning process is a multi-phase and multi-physicical process with flow, electric and magnetic fields coupled together. This paper deals with establishing a multi-phase model for numerical study and explains how to prepare for nanofibers and nanoporous materials. The model provides with a powerful tool to controlling over electrospinning parameters such as voltage, flow rate, and others

    Electrospun Nanofiber Yarns for Nanofluidic Applications

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    This dissertation is centered on the development and characterization of electrospun nanofiber probes. These probes are envisioned to act like sponges, drawing up fluids from microcapillaries, small organisms, and, ideally, from a single cell. Thus, the probe performance significantly depends on the materials ability to readily absorb liquids. Electrospun nanofibers gained much attention in recent decades, and have been applied in biomedical, textile, filtration, and military applications. However, most nanofibers are produced in the form of randomly deposited non-woven fiber mats. Recently, different electrospinning setups have been proposed to control alignment of electrospun nanofibers. However, reproducibility of the mechanical and transport properties of electrospun nanofiber yarns is difficult to achieve. Before this study, there were no reports demonstrating that the electrospun yarns have reproducible transport and mechanical properties. For the probe applications, one needs to have yarns with identical characteristics. The absorption properties of probes are of the main concern. These challenges are addressed in this thesis, and the experimental protocol and characterization methods are developed to study electrospun nanofiber yarns

    BaFe12O19 single-particle-chain nanofibers : preparation, characterization, formation principle, and magnetization reversal mechanism

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    BaFe12O19 single-particle-chain nanofibers have been successfully prepared by an electrospinning method and calcination process, and their morphology, chemistry, and crystal structure have been characterized at the nanoscale. It is found that individual BaFe12O19 nanofibers consist of single nanoparticles which are found to stack along the nanofiber axis. The chemical analysis shows that the atomic ratio of Ba/Fe is 1:12, suggesting a BaFe12O19 composition. The crystal structure of the BaFe12O19 single-particle-chain nanofibers is proved to be M-type hexagonal. The single crystallites on each BaFe12O19 single-particlechain nanofibers have random orientations. A formation mechanism is proposed based on thermogravimetry/differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and transmission electron microscopy (TEM) at six temperatures, 250, 400, 500, 600, 650, and 800 �C. The magnetic measurement of the BaFe12O19 single-particle-chain nanofibers reveals that the coercivity reaches a maximum of 5943 Oe and the saturated magnetization is 71.5 emu/g at room temperature. Theoretical analysis at the micromagnetism level is adapted to describe the magnetic behavior of the BaFe12O19 single-particle-chain nanofibers

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    Department of Energy Engineering (Energy Engineering)With the demand to overcome the issues concerning environmental pollution of fossil fuel in large-scale system and various fields, numerous efforts have been devoted toward a design of rational energy storage system (ESS) in order to substitute present energy source. While lots of systems are suggested, lithium-ion batteries (LIBs) have been attracted as one of the promising ESS among various storage devices. Existing one which consists of a graphite anode unfortunately have the trouble to fulfilling required condition such as high power and energy density. Thus, new type of anode materials has been developed to achieve mentioned specifications. As possible candidates, silicon (Si) and germanium (Ge) have been emerged owing to their high gravimetric/volumetric capacity and low operating voltage. Nevertheless, those materials remain under challenge level because inferior electronic properties have the limit to catch high power density and unexpected volume expansion on a lithiation process into materials, resulting in the electrode failure and capacity decay where factors influence safety and stability issues in LIBs system. Here, we introduce approaches through dimensional manipulation to proceed. Overall synthetic processes are focused on versatile method, a possibility of mass production and evaluation methods obviously demonstrate intrinsic/extrinsic characteristic ways. With in situ microscopic/electrochemical techniques, specific properties and electrochemical reaction mechanism of synthesized materials are clearly unveiled to facilitate power density enhancement and volume change suppression. In Chapter II, we present zero-dimensional (0D) carbon wrapped-hollow Si microparticles which possess porous shell structure from various silica source regardless of their shape. Sequent top-down and bottom-up processes fabricate uniform 0D Si and a key factor for unique formation mechanism is verified through ex situ characterization and simulation results. In electrochemical view, creating cavities in a core and pores in the shell alleviate volume expansion and enable short ion-diffusion length. Surface carbon layer additionally provide fast electron movement to guarantee stable and considerable power density. Besides, in situ transmission electron microscopic (TEM) demonstrate the stability of morphological structure on charge/discharging cycle. In Chapter III, we design one-dimensional (1D) Ge/zinc (Zn)-based nanofibers. Homogeneous Ge/Zn nanofibers via electrospinning method and solid-gas reduction reaction own atomic-level distribution of each element. Well-dispersive metallic Zn in Ge nanofiber could effectively improve electronic conductivity/volumetric stability and nanosized structure also features facile ion transport and stress release by volume expansion on electrochemical cycles. In situ TEM/electrochemical impedance spectroscopy (EIS) deeply investigate the critical role of ionic bond of Zn element in Ge nanofibers. In Chapter IV, we introduce additional 1D Ge nanofibers, which feature numerous sizes of pores in whole morphological structure. Intrinsic metal oxide characters based on Ellingham diagram enable to carve heterogenous pore in and out of nanofibers. This structure shows stable electrochemical cyclability without a large volume expansion. Further, we confirm the unique behavior of Ge, called memory effect in LIBs. In situ TEM characterization supports that numerous pores work as volume buffer sites and keep spatial reversibility on charge/discharge cycles. In Chapter V, we finally suggest synthetic method of three-dimensional (3D) porous Ge clusters from zeotype-borogermanate microcubes, artificial Ge-rich zeolite. This starting material is prepared in a large quantity through a simple hydrothermal process as followed by sequential thermal and etching treatment to produce 3D porous Ge. As-fabricated product interestingly behaves like a pseudocapacitance exhibiting fast electrochemical kinetics. Further, the as-formed pores build up stable solid electrolyte interphase (SEI) layer on the surface for prolonged cycles, improving cycle stability. In Chapter VI, we briefly provide the insight for the correlation of the dimensions and electrochemical properties toward advanced lithium storage system. To handle unsettled issues in large-scale lithium batteries, it is essential to look around the overall circumstances to match the specific purpose.clos

    Chasing μ

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    Conducting and semiconducting, π-conjugated polymers are promising materials for micro- and nano-optoelectronic applications because of their widely tunable physical, electrical, and optical properties. These polymers have been used to fabricate a number of electronic devices including field-effect transistors, light-emitting diodes, and photovoltaic cells. However, widespread commercial application of these devices has yet to be realized, due in part to poor electronic transport characteristics and device degradation. Nanostructuring of conjugated polymers by various methods has demonstrated marked improvements in molecular ordering and electronic transport. In this research, nanoscale, tubular structures of semiconducting polymers fabricated by template wetting nanofabrication procedures are explored. In particular, confinement-induced effects on the electronic carrier transport property mobility, μ, were investigated for both highly ordered and amorphous polymers. Analysis of space-charge-limited currents provided the key means of monitoring transport characteristics and molecular order. The effects of chemical filtration, nanotube diameter, solvent selection, and temperature are examined in detail

    Modeling electrospun nanofibers: An overview from theoretical, empirical, and numerical approaches

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    Electrospinning is a sophisticated material process to manufacture well-tailored nanofibers for fiber reinforcement, tissue scaffolding, drug delivery, nanofiltration, cosmetics, and protective clothing. Abundant information and knowledge are reported from experimental observation and material characterization to determine and control nanofiber properties. However, experimental results need to be interpreted systematically through theoretical, analytical, and numerical models for the optimization of fiber diameter and alignment, porosity, and estimation of mechanical properties of electrospun nanofibers. This paper provides a comprehensive review on current status of modeling approaches used in electrospun nanofibers to elucidate their systematic research approaches including material fabrication, experimental characterization, and modeling

    Light-triggered CO release from nanoporous non-wovens

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    The water insoluble and photoactive CO releasing molecule dimanganese decacarbonyl (CORM-1) has been non-covalently embedded into poly(l-lactide-co-d/ l-lactide) fibers via electrospinning to enable bioavailability and water accessibility of CORM-1. SEM images of the resulting hybrid non-wovens reveal a nanoporous fiber morphology. Slight CO release from the CORM-1 in the electrospinning process induces nanoporosity. IR spectra show the same set of carbonyl bands for the CORM-1 precursor and the non-woven. When the material was exposed to light (365-480 nm), CO release from the incorporated CORM-1 was measured via heterogeneous myoglobin assay, a portable CO electrode and an IR gas cuvette. The CO release rate was wavelength dependent. Irradiation at 365 nm resulted in four times faster release than at 480 nm. 3.4 μmol of CO per mg non-woven can be generated. Mouse fibroblast 3T3 cells were used to show that the hybrid material is non-toxic in the darkness and strongly photocytotoxic when light is applied
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