Dissertation/Thesis Abstract

Online impedance spectroscopy of thermoset nanocomposites for materials in situ process control
by Jacobs, John David, Ph.D., University of Cincinnati, 2009, 331; 3371010
Abstract (Summary)

The goal of this work is to appeal to both the scientific and engineering communities through the purposeful integration of sensors, models, and controls technology to develop a comprehensive thermoset nanocomposite materials processing system with in situ dielectric characterization and electric-field directed morphology capabilities. This may, in turn, provide a systematic path towards a better scientific understanding of nanocomposite dielectric materials, as well as novel methods relevant to feedback process control strategies for next generation nanocomposite materials.

A nanocomposite material process control system incorporating online impedance spectroscopy, automated environmental control (temperature and pressure), and electric-field actuation into a modular and extensible control platform is designed and used to investigate thermoset nanocomposite dielectric materials. Specifically, this work emphasizes the development of online sensing based on impedance spectroscopy (1Hz to 1MHz) to detect in situ material properties and features related to charge transport, morphology, and molecular dynamics (across a wide range of length-scales) that evolve during nanocomposite processing. This system also features the unique ability to actuate nanocomposite materials using applied AC electric fields. This control affects the statistical alignment of nano-particles through electrophoretic forces induced on the particle interfacial surfaces, thereby directing material morphology (i.e., rotational alignment of nanofiller along the applied electric-field direction) which can subsequently be “locked in” upon thermoset crosslinking.

Although the techniques developed here are applicable to a wide range of nanocomposite and dielectric materials, the subclass of organically-modified layeredsilicate thermosets is used as the model system for development.

Demonstration of the thermoset process control system is established through key experiments performed to investigate effects of nanoclay loading, impact of excess nanoclay surface modifier (i.e., excess surfactant); ionic conductivity cure monitoring; and thermoset morphologies. Directed morphology using electric-field actuation is exercised and a simple dielectric analysis is provided.

This effort may have significant impact on existing impedance-related sensing techniques, such as dielectric cure monitoring, by enabling access to material states and properties that were previously unobservable. Equally important is the foundation this technology may provide for the development and discovery of more sophisticated nanocomposite material process control methods. Novel control architectures based on morphology sensing may facilitate the ability to harness the processing techniques required for future advancement of materials and devices with all of the performance-enhancing properties afforded by nanocomposites.

Indexing (document details)
Advisor: Garrett, Patrick
School: University of Cincinnati
School Location: United States -- Ohio
Source: DAI-B 70/08, Dissertation Abstracts International
Subjects: Electrical engineering
Keywords: Dielectrics, Layered silicates, Online impedance spectroscopy, Thermoset nanocomposites
Publication Number: 3371010
ISBN: 978-1-109-35915-2
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