Piezoelectric Polymer Nanocomposite Materials: Device Design and Fabrication Methods
- Author(s): Kim, Kanguk
- Advisor(s): Sirbuly, Donald J
- et al.
Piezoelectric materials are one of the most important components in various applications including energy harvesting platforms, sensors, and actuators due to their ability to directly convert mechanical energy to electrical energy or vice versa. The typical requirements for piezoelectric materials are low processing costs, high piezoelectric coefficients for sensitivity, mechanical resilience, as well as simple processing strategies. Over the past decade, nanostructured piezoelectric materials have been rigorously studied and energy conversion efficiencies and power outputs of piezoelectric materials have steadily increased. In spite of recent advancements there are still serious limitations for these materials including inefficient means of harnessing non-mechanical energy sources, extreme difficulties in fabricating complex piezoelectric structures, poor mechanical flexibility for integration into non-planar configurations, and an incomplete understanding on the underlying factors that influence piezoelectric performance.
To address some of the aforementioned limitations of piezoelectric materials, this dissertation is divided into two parts. In the first part, a novel piezoelectric energy conversion platform will be presented that can harness mechanical and/or non-mechanical energy sources (e.g., heat) The device geometry leverages an array of vertically aligned ZnO nanowires embedded in an environment-responsive polymer matrix to generate direct current outputs. It is found that the interface between the polymer matrix and piezoelectric element is a key parameter to tune the performance of the device and funnel stress more efficiently to the piezoelectric crystal. This stress management concept within the composite material is supported both by experimentation and simulations.
In the second part, a new optical fabrication tool is described that allows exceptional control over size and shape of piezoelectric materials. The technique relies on a colloidal solution that contains piezoelectric nanoparticles suspended in a photoliable polymer and exposing to user-defined digital optical masks. Initial experiments were carried out on barium titanate (BaTiO3 – BTO) nanoparticles in a polyethylene glycol diacrylate (PEGDA) polymer, but the process is general for other piezoelectric nanomaterials and photoactive polymers. By dynamically altering the digital optical masks and controlling the focal plane of the masks, 3D microstructures can be fabricated in mere seconds. To enhance the piezoelectric properties of the printed nanocomposites, the piezoelectric nanoparticles can be chemically modified with linker molecules that cross-link with the polymer chains under light exposure. This nanoparticle-polymer interface is critical for boosting the efficiency of stress transfer from the polymer matrix to the piezoelectric crystal and is a key parameter in understanding the limits of piezoelectric performance.