Title

Development of Conductive Silver Nanocomposite-Based Sensors for Structural and Corrosion Health Monitoring

Date of Award

6-1-2021

Degree Name

Ph.D. in Educational Leadership

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Khalid Lafdi

Abstract

In this study, silver/epoxy conductive nanocomposite-based sensors were developed as follows: First, abundant silver nanomaterials were synthesized using a rapid polyol reduction method. Factors that affected silver nanomaterial morphology and the mechanism of nanosilver growth in large-scale synthesis were studied in detail. Controlling the silver nanomaterial's size and uniformity and efficiently purifying the silver nanowire were the main challenges in the development of large-scale synthesis. Second, the morphology, crystallinity, and orientation of various silver nanofillers were characterized. Then, silver nanoparticle/polyacrylonitrile and silver nanowire/polyacrylonitrile-based nanocomposites were fabricated by spin coating and used to investigate the silver nanocomposite conductive network. Silver nanowire-based nanocomposite showed a lower percolation threshold. A conductive unit-based model was established and successfully explained the evolution of the conductive network and aggregation. The aggregation geometry of nanofiller appeared as a dominant factor in altering the percolation behavior. Small-sized, irregularly shaped silver nanoparticle aggregates can lower the percolation threshold by introducing anisotropy to the nanocomposite. In contrast, large-sized, irregularly shaped silver nanoparticle aggregates hinder the formation of the conductive network due to the number of aggregates decreasing. Lastly, the silver conductive nanocomposite-based structural health monitoring sensors were designed to detect the progress of chemical diffusion and material degradation as a function of time. A comparison study between the silver nanowire/epoxy sensor and silver nanoparticle/epoxy sensor was conducted to investigate the concentration and geometry of the silver nanomaterial's effect on acid penetration. It appeared that the structural health monitoring sensors' resistance decreased in three stages as the diffusion time progressed. When the volume percentage of silver nanomaterial increased, the electrical resistance-time curve became less smooth, which was considered as conductive network formation affecting the sensing behavior. Moreover, with the increase in volume percentage of silver nanomaterial, response time decreased.Furthermore, the silver nanowire-based sensors showed a shorter response time, and with the volume percentage of silver nanomaterial increase, the difference became dominant. Modeling work based on Fick's second law was conducted using MATLAB to study the geometry effect of silver nanoparticle, silver nanoparticle aggregate, and silver nanowire on acid penetration progress. The higher aspect ratio of nanofiller resulted in a higher effective diffusion coefficient. Thus, improved durability of the nanocomposite is expected with excellent dispersion of nanofillers.

Keywords

Materials Science, Chemical Engineering, silver nanomaterials, nanomaterials synthesis, conductive nanocomposite, percolation model, structural health monitoring, sensor, ion diffusion, modeling

Rights Statement

Copyright 2021, author

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