Polymer-based nanocomposites are becoming an attractive set of organic-inorganic materials due to their multifunctionality and many potential applications. The aim of this project is to develop a novel electroactive polymeric composite for multifunctional applications that require self-sensing and self-actuation capabilities. We propose to design wide nanowires-polymer composites whose morphology in the polymer matrix is micro-tailored by external fields. The goal is to achieve controlled alignment and dispersion of nanowires in the polymer matrix, resulting in a composite that combines electrostrictive and piezoelectric properties. Electromechanical response of such nanocomposite is expected to exceed the best single-phase ceramics, polymers or thin films currently available and preserve advantages of the polymers. The combination of superb properties of nanomaterials with the lightweight, flexibility, and manufacturability of dielectric polymers provides the route for future generations of multifunctional materials. The novel nanocomposites will have tremendous impact in intelligent materials and structure applications, including piezoelectric sensors and actuators, biological sensors, structural health monitoring and vibration control in numerous industrial, civil, medical and aerospace applications.
The research will involve graduate student and undergraduate education and training. Graduate and undergraduate student researchers will be trained to work on nanomaterials fabrication, property characterization, and device design and evaluation. Research Experience for Undergraduates (REU) will be created for students from underrepresented groups through the Summer Engineering Academy (SEA) program coordinated by the Pitt Engineering Office of Diversity. This project will also provide hands-on research training opportunities for K-12 students each summer semester through Pitt Engineering Career Access Program (PECAP). The research topics in this project will be incorporated into a new course on Nanomaterials and Devices for senior undergraduate and graduate students.
Project Summary: This project aimed to fabricate novel multifunctional polymer nanocomposites and to exploit their properties for the development of inherently directional dynamic sensing and actuation devices. We proposed to design nanotubes, nanowires, and fiber composites whose morphology in the polymer matrix is micro-tailored to have unique electromechanical properties for sensing and actuation. The devices fabricated from the nanocomposites can be integrated with general micro fabrication processing to form sensors and actuators for a broad range of MEMS devices such as microphone sensors, micro-accelerometers, breath sensors, strain and stress sensors, and micro pumps, etc. Broader Impact: The research also involved graduate student and undergraduate education and training. Graduate student and undergraduate students were trained in state-of-the-art methods of nanomaterials fabrication, property characterization, and device design and evaluation, providing a workforce well qualified for industrial and academic research. The research activities proposed in this project have been incorporated into new courses for both undergraduate and graduate student as advanced topics. Research Outputs 1. Technology development for batch fabrication of nanowires, nanorods, and nanotubes: Three processing methods have been applied for the batch manufacturing of functional nanomaterials and nanostructures (ZnO nanowires), including 1) microwave thermal evaporation and deposition method, 2) Hydrothermal growth in low temperature condition, and 3) SAM assisted growth. The first and third methods are new approaches we have developed in this NSF project. Microwave thermal evaporation and deposition have been developed to fabricate various ZnO nanomaterials (nanowires, nanotubes, nanorods, microtubes, etc) under different processing conditions, and using different substrates. This technique is an innovative evaporation (sublimation)-condensation approach that can be used for single crystal materials growth. The evaporation (sublimation) growth is driven by the temperature difference between the powder material source and a substrate (or single crystal seed). By microwave processing, a much higher growth temperature can be obtained to achieve high growth rates and high quality nanocrystals. High quality and well controlled growth of ZnO nanomaterials has also achieved by hydrothermal growth. Large size substrate can be used in this method to yield large quantity of ZnO nanomaterials fabrication. In addition, a unique method was developed for the controlled batch fabrication of arrayed ZnO nanowires. This is self-assembled-monolayer (SAM) assisted growth of ZnO nanowires with well-defined diameters and lengths. 2. Electric Field assisted fabrication of ZnO nanowires/polyimide composite for functional device fabrications. A field assisted alignment/distribution method was developed to fabricate the ZnO nanowires/polymer composites with multifunctionality. Thin and thick film ZnO nanowires-polymer composites have been fabricated using interdigital transducer electrode configuration. The devices formed by using the IDT and nanocomposites demonstrated unusual dielectric properties, piezoresistive properties, and tunable electrical polarization. 3. Acoustic wave gas sensors with ZnO nanowires grown on the surface are being developed for intermediate and high temperature sensing applications. 4. Piezoresistive properties of ZnO nanowires/polymer nanocomposite films have been systematically studies. Large gauge factors are obtained for the nanocomposites strain sensors. Strain sensors were applied both static and dynamic strain detection. 5. Comparison study was also extended to the property of carbon nanotube/polyimide nanocomposites for strain sensing, and gas sensing application. 6. Low frequency vibration and strain sensors using anisotropic ZnO nanowires/polymer nanocomposites have been studied. The comparison with PZT fiber/polymer composites was also explored. 7. Three PhD students were supported or partially supported by this project to conduct PhD dissertation research on nanomaterials, piezoresistive sensors and piezoelectric sensors. 8. Two undergraduate students were offered summer Research Experience for Undergraduate (REU) in in this project. The summer program provided full time research training for the students for a period of 12 weeks in each summer. These students closely worked with graduate students in the nanomaterials and device group and the PI to gain a unique research experience in the emerging nano-manufacturing field. During the course of the summer program, the students were trained to be able to carry out a planned series of experiments, including: 1) fabrication of nanomaterials and nanostructure by using the microwave evaporation-deposition method; 2) electrical filed–assisted alignment of ZnO nanowires in liquid phase polyimide to form multifunctional nanocomposites; 3) fabrication of interdigital electrodes on top of nanocomposite thin films; 4) dielectric, piezoresistive, and piezoelectric property characterization of ZnO nanowires and CNT/polymer composite film transducers. 9. K-12 outreach activity in this project was arranged by offering a local high school honor student a summer research opportunity. The research activity was on the piezoresistive nanocomposite thin film sensor for tensile strain test using a small tensile tester. 10. The research discoveries have been incorporated in two graduate courses, ME 2080 Introduction to Micro and Nanofabrication, and ME 2082 Principles of Electromechanical Sensors & Actuators.
