Characterization and Modeling of Piezo-Resistive Properties of Carbon Nanotube-Based Conductive Polymer Composites

• Other Authors: Pham, Giang Truong, 1971- (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Industrial engineering; Manufacturing processes
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-1965

Electrically conductive polymers (ECPs), offering capabilities such as electrostatic discharge protection and electromagnetic interference shielding, have been the subject of intensive research and development both in academia and industry. The emergence of new conductive nano-fillers in recent decades, particularly carbon nanotubes (CNTs), further fuels more enthusiasm. Thanks to CNTs' excellent mechanical, thermal, and electrical/electronic properties, CNT-filled polymers possess not only conductive properties, but a range of other properties desirable for multi-functional and high performance applications. In order to fully exploit the benefits of CNT-based conductive polymers (CNT-ECPs), researchers have conducted diverse studies primarily to characterize the electrical conductivity of the composites. A crucial area that is less studied is the piezoresitive behaviors of CNT-ECPs, that is, the change in material conductive properties due to an applied stress or strain. Given broad usage of ECPs, it would be reasonable to assume that ECP products commonly operate under certain stress or strain conditions. For instance, an electrostatic discharge (ESD)-protected conductive coating for spacecraft would be affected by strain induced by mechanical or aerodynamic loads. A more systematic understanding of the materials' piezoresistivity, therefore, is instrumental in ensuring satisfactory conductive performance of those material applications. Additionally, knowledge of conductive characteristics of the CNT-ECPs against stress/strain can open the door to newer material applications, e.g., strain gage or multifunctional conductive coating with strain-sensing capability. This research aims to achieve a more fundamental understanding of the mechanism of piezoresistive property of CNT-ECPs, and to develop a model that permits quantifying the structure-property relationships of CNT-ECPs' piezoresistivity. In this research, expanded experimental studies with various thermoplastic CNT-ECPs revealed that piezoresistivity in CNT-ECPs is dominated by changes in inter-tube resistances. Additionally, the gauge (sensitivity) factors of the CNT-ECPs follow an exponential relationship with (v – vc), where v is the volume concentration of CNT in the composite and vc is the tube volume concentration at its percolation threshold. The model development effort yielded a semianalytical piezoresistivity model capable of analyzing and predicting piezoresistivity in three-dimensional CNT-ECP samples. The model is most applicable to systems with straight short MWNTs randomly dispersed in thermoplastic polymers. === A Dissertation Submitted to the Industrial & Manufacturing Engineering Department in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. === Fall Semester, 2008. === November 07, 2008. === Nanocomposite, Sensor, Percolation Theory === Includes bibliographical references. === Zhiyong (Richard) Liang, Professor Directing Dissertation; Chuck Zhang, Committee Member; Joseph J. Pignatiello, Jr., Committee Member; Young-Bin Park, Committee Member; Petru Andrei, Outside Committee Member.