자료유형  

 학위논문

Control Number  

0017164449

International Standard Book Number  

9798346383505

Dewey Decimal Classification Number  

621

Main Entry-Personal Name  

Saikia, Nayan Jyoti.

Publication, Distribution, etc. (Imprint  

[S.l.] : The Pennsylvania State University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

144 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-05, Section: A.

General Note  

Advisor: Hickner, Michael A.

Dissertation Note  

Thesis (Ph.D.)--The Pennsylvania State University, 2024.

Summary, Etc.  

요약Ion exchange membrane (IEMs) are poised to play an important role in emerging energy conversion devices such as batteries, soft actuators and electrochemical cells, especially polymer-electrolyte-membrane fuel-cells (PEMFCs). IEMs are typically composed of a hydrophobic backbone which is covalently attached to an ionic group with a mobile counter-ion. The ion functionalized group dissociates in the presence of water releasing the counter ion and hence is responsible for ionic conduction. These materials are often called single ion conductors since only one charge is mobile, versus a salt-based ionic conductor where both anions and cations are mobile in the matrix. In IEMs conduction of counterions rely on a network of water-fille domains to transport the ion through the polymeric matrix. An effective network in the bulk provides for faster transport than an unorganized system, and hence high ionic conductivity of the ensuing material.Researchers have been interested in investigating these ionic domain networks (or microphase separated morphology) since the early days of small angle x-ray scattering (SAXS). SAXS is a fast technique that generates contrast based on electronic density between the phases. This allowed them to investigate the morphology of Nafion and propose representative structures that explain the superior ionic conductivity of the material. However, scattering alone cannot unambiguously elucidate the morphology since it relies on models to fit the experimental data, and hence TEM should be used in tandem with SAXS. In this dissertation, we will employ transmission electron microscopy (TEM) as a tool to understand the phase morphology of ionic polymers and directly visualize size, shape, and distribution of domains in the materials. Apart from this, we will use the different modalities such as field/dark field (BF), scanning transmission electron microscopy (STEM) and energy filtered TEM (EFTEM) to optimize contrast and resolution of the images.It has been well-established that polymeric materials undergo beam damage under irradiation. Radiation damage changes morphology due to heating, electrostatic charging, and sputtering and can produce artifacts that are not inherent to the unaltered material. To mitigate damage, we begin our experiment at low dose rates ( 500 e/nm2s) and slowly increase the beam intensity to make sure radiation damage is minimized. STEM modes were controlled using spot sizes and lenses to achieve variable current. We observed that STEM mode is a more efficient way to image polymers as the contrast can be switched based on atomic number of the elements present or the density variations between the phases. Density variations allowed us image ionic block copolymers based on two common backbone architectures: polystyrene-b-polybutadiene-b--polystyrene (SBS) and polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS). The SEBS-based polymer demonstrated long range perforated lamellar structures with average lamellar thickness of 55 nm while the morphology of SBS polymers were heterogenous without widespread long-range order. Some local ordering was observed in the SBS samples of length scales of about ~150 nm which indicates non equilibrium conditions for the bulk film, but block architecture and ion content can also play a big role in nanophase morphology. In general, these ionic block copolymers demonstrated deviation in phase morphology from traditional block copolymers, which can be attributed to the additional interaction that the ions have on the polymer system.

Subject Added Entry-Topical Term  

Fuel cells.

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Software.

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Humidity.

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Acids.

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Protons.

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Water.

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Sulfur.

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Fluorides.

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Research & development--R&D.

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Energy consumption.

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Caustic soda.

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Nitrogen.

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Membranes.

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Polymers.

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Transmission electron microscopy.

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Chloride.

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Carbon black.

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Permeability.

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Copolymers.

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Geometry.

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Alternative energy.

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Analytical chemistry.

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Atomic physics.

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Chemical engineering.

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Nanotechnology.

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Polymer chemistry.

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Literature.

Added Entry-Corporate Name  

The Pennsylvania State University.

Host Item Entry  

Dissertations Abstracts International. 86-05A.

Electronic Location and Access  

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Control Number  

joongbu:656964