Date of Award

8-1-2018

Document Type

Dissertation

Degree Name

Ph.D.

Department

Materials Science

First Advisor

Maciej Kumosa, Ph.D.

Abstract

Silicone rubber materials are frequently used in extreme environments, including aviation, space, high voltage and other applications. In service, however, complex and difficult to predict damage mechanisms in the rubbers can occur which can lead to severe failures of essential infrastructural components. For example, Non-Ceramic Insulators (NCIs), which support some of the most critical high voltage lines in the world, regularly exhibit severe polymer aging due to environmental pollution, ultra-violet (UV) radiation, and dry band and corona arcing. Designing silicone rubbers to resist aging in these demanding environments is difficult and requires an interdisciplinary approach, including correctly assessing the actual aging factors. This work attempts to determine the actual causes of NCI aging in coastal high voltage environments, and to demonstrate that extreme aging of silicone rubbers can be mitigated through the inclusion of titanium dioxide (TiO2) microparticles. In-service aging of NCIs in salt rich environments was attributed for the first time to the formation of highly oxidizing hypochlorous acid, which forms in the presence of aqueous salt and minimal voltage. The addition of TiO2 was found to significantly improve the resistance of a polydimethylsiloxane (PDMS) material to aging by about 50% in HOCl and electrolyzed aqueous salt. Using molecular dynamics, it was shown that PDMS methyl group reorientation at the nanoscale level causes numerous macroscale effects including, an increase in hydrophobicity and decrease in permeating compound diffusion.

In the second part of this study the experimental and numerical approaches developed for the extreme NCI aging problem were used to improve our understanding of ice adhesion and accumulation on silicone rubber surfaces used as icephobic barriers. The barriers were improved for their resistance to ice adhesion by 80% by embedding TiO2 particles and this positive outcome was attributed mostly to the lotus effect. However, the embedded particles did not prevent ice accumulation on the barriers, especially under the most extreme icing condition associated with the rapid cooling of mist size water droplets. The entire research presented in this dissertation was enhanced by a unique combination of nanotechnology, molecular dynamics, 3D physics modeling, and experimental approaches.

Provenance

Received from ProQuest

Rights holder

Monika Bleszynski

File size

169 p.

File format

application/pdf

Language

en

Discipline

Materials Science, Nanotechnology, Mechanical engineering

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