Title

Development of Nanocomposites Based Sensors Using Molecular/Polymer/Nano-Additive Routes

Author

Chang Liu

Date of Award

1-1-2019

Degree Name

Ph.D. in Materials Engineering

Department

Department of Chemical, Materials and Bioengineering

Advisor/Chair

Advisor: Khalid Lafdi

Abstract

In this study, multiple approaches were explored for building advanced nanocomposite sensors intended for use in fiber reinforced organic matrix composite structures. One expected application of such technology is sensing of chemical penetration in the walls of large chemical tanks. The work described herein involved development and characterization of various novel conductive nanocomposites from polymeric feedstocks as well as carbon nanoparticles.The first approach consisted of using pitch based, liquid crystal molecular additives to polyacrylonitrile (PAN) to create novel electrospun carbon nanofibers. Raman spectroscopy confirmed the increase of an ordered structure in PAN/pitch based carbon nanofibers by analyzing the sharpness of the G band. As a result, the addition of pitch increased the degree of graphene alignment because of the high amount of liquid crystal present in the pitch. This structure led to enhanced physical properties of the carbon nanofibers.The second approach used a conductive network of conjugated polymer (polyaniline, PAni) nanoparticles dispersed in a blend of polyvinylpyrrolidone (PVP) and polyurethane (PU). PAni was synthesized using an in situ polymerization method which resulted in colloidal PAni or PAni nanowires. PAni nanowires self-assembled into scattered fractal networks. After adding PU, a concentrated PAni/PVP phase occurred. Such a phenomenon was attributed to the balance between blocking force and van der Waals force. When the surface tension is the determining factor in the 'island', the round shaped phase separation occurs. The surface tension and van der Waals force were two determining factors in the formation of bi-continuous phase separation. When the forces were in equilibrium, a fractal network structure was formed and the polymer blends were very stable. A flexible conductive fabric was successfully prepared by coating the conductive ternary mixture onto a non-woven fabric.The last approach uses carbon nanoparticles (carbon nanotube and carbon black) as PAni as additives to an epoxy matrix to alter conductivity in order to predict the chemical penetration in a composite structure. In this study, two nanocomposite formulations were produced: one is based on polyaniline and the second uses CNT as additives. These materials were dispersed in an epoxy resin system and cured into a solid plate which also contained embedded metal electrodes. The sensor assembly was then immersed in an acid solution to evaluate its ability to detect the ingress of ions. It appears as the amount of nano-additives increased, the conductivity increased and the response time towards acid penetration was shorter. The sensing mechanism was depicted using a Fickian model and the experimental and theoretical data were in agreement. Indeed, the penetration and diffusion of hydrogen ions were responsible in connecting the CNT aggregates by forming a continuous conductive network. Finally, the sensor was connected to a radio frequency based wireless system to demonstrate its ultimate use in the field.

Keywords

Materials Science, Polymers, Nanotechnology, nanomaterial, polymer, polyaniline, carbon nanofiber, CNT, carbon black, electrospinning, nanocomposite, conductive network, structural health monitoring, SHM, wireless sensing

Rights Statement

Copyright 2019, author

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