Cold Sintering of Zinc Oxide Polyimide Composites with Internally Tunable Electrical Properties via Polymer Crosslinking

open_access
Open Access
Author:
Vetser, Adam
Area of Honors:
Materials Science and Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Clive A Randall, Thesis Supervisor
Robert Allen Kimel, Thesis Honors Advisor
Keywords:
cold sintering
sintering
ceramics
polymers
composites
ceramic-polymer composites
varistors
impedance spectroscopy
polyimide
ZnO
zinc oxide
composite cold sintering
crosslinking
internal polymer crosslinking
RTM370
Abstract:
This thesis investigates the fabrication, microstructure, crosslinking, and bulk electrical properties of a ZnO polyimide composite. Single step processing for ceramic-polymer composites has been unattainable due to the gap between ceramic and polymer processing temperatures using traditional sintering methods >1000°C. The cold sintering process (CSP) of ZnO occurs at 250°C, allowing for the integration of polymeric materials below their crosslinking temperature without degradation. Five methods of dispersing the polyimide in ZnO were investigated with the goal of obtaining a homogenous polymer dispersion and high density. Integration of the polyimide to ZnO through the creation of a polymer dispersion in an organic solvent yielded a 94.7% relatively dense composite. Electrical impedance spectroscopy (EIS) was used to characterize the bulk electrical properties of the composite before and after crosslinking at 380°C. Resistivity was shown to decrease by an order of magnitude while the activation energy for electron conduction increased after crosslinking. A mechanism for polyimide crosslinking was proposed using Fourier-transform infrared spectroscopy (FTIR) to explain the observed electrical trends. Ceramic-polymer composites offer applications including semiconductors, piezoelectrics, varistors, and solar cells. The development of single step ceramic-polymer composite processing could allow for devices with internally tunable electrical properties as a function of applied heat.