Degree Type

Dissertation

Date of Award

2015

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

Major

Materials Science and Engineering

First Advisor

Nicola Bowler

Abstract

Capacitive polymer-matrix composites (PMCs) were fabricated with various nanofillers, defined as nanodielectrics. Surface modification of nanofillers was conducted to improve the homogeneity of nanocomposites. A capacitive sensor was designed and fabricated to measure dielectric properties of thermally aged cable jackets for the purpose of nuclear power plant (NPP) cable status monitoring.

Silanized-Si/epoxy nanocomposites were studied for structural capacitors. The surface treatment of Si nanoparticles by silane coupling agents was achieved to improve dispersion of nanofillers in an epoxy matrix. The nanocomposite shows an increase of dielectric breakdown strength and dielectric constant with no significant increase in loss tangent at 10 wt.% silanized-Si loading. Furthermore, the introduction of silanized nano-Si increases the storage modulus of epoxy and the Tg shows good thermal stability. The silianized Si/epoxy nanocomposite is a promising material for future structural capacitors.

Dielectric properties of silanized-Si/epoxy nanocomposites were investigated for a comprehensive understanding of the nanodielectric system. Dielectric spectra of nanocomposites were fitted by Havriliak-Negami (HN) dielectric relaxation functions with a power-law conduction term. Maxwell-Wagner-Sillars (MWS) interfacial polarization relaxation was observed in silanized-Si/epoxy nanocomposites. Further, Weibull distribution analysis was applied to study the dielectric breakdown behaviors. Silanized Si/epoxy exhibits high dielectric breakdown strength and a narrow distribution of failure points.

Dielectric properties of another nanodielectric system, poly(methyl methacrylate) (PMMA)/montmorillonite (MMT), were investigated to study the effect of MMT and the interface to the polymer. The data was analyzed with a sum of HN functions and a power-law conduction term. As MMT content increases, an MWS relaxation emerges in the nanocomposites and α-relaxation is contributed by main-chain movements above T¬g. The characteristic frequency of β-relaxations is influenced by the mergence with the α-relaxation above T¬g.

A capacitive sensor was created for monitoring NPP cable jacket degradation. Ethylene propylene rubber (EPR) and cross-linked polyolefin (XLPO) cable jackets were studied in this research. Accelerated thermal aging was conducted on cable jackets. The decrease of capacitance against aging time measured on XLPO correlates well with observed changes in elongation-at-break. Capacitance of aged EPR, however, did not show a strong correlation with observed EAB for the samples studied here.

Copyright Owner

Weixing Sun

Language

en

File Format

application/pdf

File Size

119 pages

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