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The Effect of Chemical Functionality on Interfacial Dielectric Breakdown in Filled Silicone Elastomer Composites

Diebold, Roger Mitchell
Degree Grantor:
University of California, Santa Barbara. Materials
Degree Supervisor:
David R. Clarke
Place of Publication:
[Santa Barbara, Calif.]
University of California, Santa Barbara
Creation Date:
Issued Date:
Engineering, Materials Science
Self assembled monolayers
Polymer composites
Electrical insulators
Dielectric breakdown
Silane coupling agents
Dissertations, Academic and Online resources
Ph.D.--University of California, Santa Barbara, 2012

Dielectric elastomer actuators and sensors form a unique class of conformal and high strain devices whose performance is fundamentally limited by the elastomer's ability to withstand dielectric breakdown. In order to design new materials for dielectric elastomers, it is desirable to understand how breakdown occurs in these systems; a specific goal of this work is to clarify the role of chemistry in determining breakdown. For filled elastomer composites, commonly used as dielectric elastomers, the interface between matrix and filler particle is thought to be the primary region for electrical conduction. However, macroscopic investigations of such interfaces are prohibitively difficult in light of the complex and manifold factors which affect dielectric breakdown, such as material flaws and filler particle dispersion. Electrically characterizing chemically distinct but morphologically similar nanoscale interfaces allows the removal of particle-particle and other convoluting effects to isolate dielectric breakdown as a function of chemical modification.

A method is described which permits the fabrication of idealized nanoscale interfaces through vapor depositing silane coupling agents as self assembled monolayers on silicon dioxide incorporating a diffusion barrier layer. With particular emphasis on filled silicone elastomers, these idealized interfaces are probed electrically at high fields in order to gain insight into how silane coupling agent functionality affects dielectric breakdown.

Through Weibull and I-V analysis, conductive atomic force microscope breakdown experiments in 'strike' through the thickness of the organic monolayer on silicon native oxide reveal that fluorinated moieties suppress tunneling and improve breakdown resistance relative to their hydrocarbon analogues, attributable to the electron attaching ability of the highly electronegative fluorine atom. Additionally, a nanoscale test structure is fabricated to investigate surface breakdown in 'creep' at the interface between a silicone elastomer encapsulant and a chemically functionalized silicon dioxide substrate. Breakdown is found to occur primarily within two siloxane bond lengths outward from the oxide surface, and is heavily influenced by the presence of strongly bound 'ice like' water acting as a deep electron trap. Hydrogen bonding between different surface species is found to dictate the breakdown characteristics rather than silane coupling agent R group chemistry. Numerical simulations approximating creep breakdown reproduce qualitatively the Weibull characteristics observed in the experimental data.

Physical Description:
1 online resource (259 pages)
UCSB electronic theses and dissertations
Catalog System Number:
Inc.icon only.dark In Copyright
Copyright Holder:
Roger Diebold
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