DEVELOPMENT OF NANOCOMPOSITES BASED SENSORS USING MOLECULAR/POLYMER/NANO-ADDITIVE ROUTES Dissertation Submitted to The School of Engineering of the UNIVERSITY OF DAYTON In Partial Fulfillment of the Requirements for The Degree of Doctor of Philosophy in Engineering By Chang Liu Dayton, Ohio May 2019 DEVELOPMENT OF NANOCOMPOSITES BASED SENSORS USING MOLECULAR/POLYMER/NANO-ADDITIVE ROUTES Name: Liu, Chang APPROVED BY: ________________________________ _________________________________ Khalid Lafdi, Ph.D. Donald A. Klosterman, Ph.D. Advisory Committee Chairman Associate Professor Professor; Wright Brothers Endowed Department of Chemical & Materials Chair in Nanomaterials Engineering Department of Chemical & Materials Engineering ________________________________ _________________________________ Erick S. Vasquez, Ph. D. Vikram K. Kuppa, Ph.D. Committee Member Committee Member Assistant Professor Research Scientist Department of Chemical & Materials University of Dayton Research Institute Engineering ________________________________ _________________________________ Robert J. Wilkens, Ph.D., P.E. Eddy M. Rojas, Ph.D., M.A., P.E. Associate Dean for Research and Innovation Dean Professor School of Engineering School of Engineering ii © Copyright by Chang Liu All rights reserved 2019 ABSTRACT DEVELOPMENT OF NANOCOMPOSITES BASED SENSORS USING MOLECULAR/POLYMER/NANO-ADDITIVE ROUTES Name: Liu, Chang University of Dayton Advisor: Dr. Khalid Lafdi 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. iii 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. iv DEDICATION Dedicated to my parents Yumen Liu & Aizhu Zhang v ACKNOWLEDGEMENTS My special thanks are giving to Dr. Khalid Lafdi, my advisor and friend, for providing the time, material and equipment necessaries, for guiding me to be a competent researcher, for directing this dissertation and bringing it to an accomplishment patiently and professionally, for being a kind and inspiring mentor. Great thanks to my committee members for their guidance. I would also express my appreciation to everyone who helped me. This includes but not limited to Dr. Donald A. Klosterman, Dr. Erick S. Vasquez, Dr. Cao Li, Dr. Francisco Chinesta, Dr. Abdulaziz Baçaoui, Robyn Braford, Qichen Fang, Yuhan Liao, Jean-Baptiste Dumuids, Nuha Al Habis, Saja M. Nabat Al-ajrash, Ali A. Muhsan, Tseng-Hsiang Ho, Robert Busch, and Shuangshan Li. The support and accompany from Yufei Liu is invaluable. vi TABTLE OF CONTENTS ABSTRACT .................................................................................................................................... iii DEDICATION ................................................................................................................................. v ACKNOWLEDGEMENTS ............................................................................................................ vi LIST OF FIGURES ........................................................................................................................ ix LIST OF TABLES ........................................................................................................................ xiii LIST OF EQUATIONS ................................................................................................................ xiv LIST OF ABBREVIATIONS AND NOTATIONS ...................................................................... xv 1. CHAPTER I INTRODUCTION ...................................................................................................... 1 1.1 Nanocomposites ............................................................................................................ 1 1.2 Nano-additives .............................................................................................................. 2 1.3 Nano Fabrication ........................................................................................................... 5 1.4 Conductive Network ..................................................................................................... 8 1.5 Structural Health Monitoring ........................................................................................ 8 1.6 Thesis Statement ........................................................................................................... 9 2. CHAPTER II THE EFFECT OF CARBONACEOUS MOLECULAR ADDITIVE ON ELECTROSPUN CARBON NANOFIBER .................................................................................. 11 2.1 Background ................................................................................................................. 11 2.2 Materials and Characterization ................................................................................... 14 2.3 Results and Discussion ............................................................................................... 15 2.4 Conclusion .................................................................................................................. 25 3. CHAPTER III SELF-ASSEMBLY AND SURFACE TENSION INDUCED FRACTAL CONDUCTIVE NETWORK IN TERNARY POLYMER SYSTEM ........................................... 27 3.1 Background ................................................................................................................. 27 3.2 Materials and Characterization ................................................................................... 29 3.3 Results and Discussion ............................................................................................... 30 3.4 Conclusion .................................................................................................................. 39 4. CHAPTER IV CNT AND POLYANILINE BASED SENSORS FOR THE DETECTION OF ACID PENETRATION IN POLYMER COMPOSITE ................................................................ 41 vii 4.1 Background ................................................................................................................. 41 4.2 Materials and Methods ................................................................................................ 44 4.3 Result and Discussion ................................................................................................. 47 4.4 Conclusion .................................................................................................................. 56 5. CHAPTER V FABRICATION OF HIGH PERFORMANCE NANOCOMPOSITE BASED CHEMICAL SENSOR USING LOW CONCENTRATION ADDITIVES .................................. 58 5.1 Background ................................................................................................................