Continuous Twisted Nano-fibrous Yarns for Smart Piezo-Textiles

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Clothing, after food, is perhaps the most common human essential, and textiles are a basic aspect of human life that has not changed from their “passive” form for many decades. Current fabrics are made of passive materials such as nylon and cotton. The goal of this project is to investigate scientific foundations to realize controllable, and reproducible production of functional smart fabrics from nano-sized smart (piezoelectric) polymer yarns, and their integration with conventional fabrics. Applications of smart textiles could include power generation and storage, personal protection, sports, fashion, communication, medical and physiological monitoring applications, and the internet of things. In particular, smart piezoelectric fabrics can be used for mechanical energy harvesting, for thermal energy harvesting through the pyroelectric effect, for ferroelectric applications, as pressure and force sensors, for motion detection, and for ultrasonic sensing. Smart fabrics will have the ability to react to different physical stimuli (mechanical, electrical, thermal, etc.) and as such can interact (sense, respond, communicate, and/or adapt) with their environment. This project will address the following challenges to realize smart piezoelectric polymer fabrics: development of processing and scale-up fabrication capabilities for production of continuous (weavable, knittable, and sewable) piezoelectric yarns; significant improvement in their electromechanical conversion efficiency; and design strategies for integration and packaging of piezoelectric yarns with conventional and conductive threads. The educational objective of the project is focused on increasing the diversity in nanotechnology-STEM through summer programs for high school students. These students will be trained on nanotechnology research, in particular smart fabrics made of piezo nanofibers. In this project, a manufacturing process based on continuous electrospinning is proposed that enables continuous production of twisted yarns. A major obstacle in the utilization of piezoelectric polymers for smart fabric applications has been the low electromechanical conversion efficiency of piezo polymers (~2%) compared to the piezo ceramics (~50%), which are inherently brittle and not suitable for smart fabric applications. The scientific outcomes of this research will be the inter-relation of thermomechanical processing, percentage of crystallinity, and orientation of crystallites and elastic and piezoelectric properties of the piezoelectric nanofibers and twisted bundles. Through fabrication and processing steps combined with computational analysis, the project will produce polymer yarns with significantly enhanced piezoelectric efficiency. This will be achieved through thermomechanical processing (thermal annealing, and drawing) designed to control the morphology (percentage of crystallinity, and orientation of crystallites), and hence properties (elastic and piezoelectric properties) and performance and output power under various external loads of piezoelectric polymer fibers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.