RUI: Laser-Zone Drawing and Annealing of High Strength Polymer Nanofibers

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This work generates new knowledge associated with laser heating of polymers to engineer and manufacture high strength nanofibers. The scientific knowledge and technological advances generated in the areas of polymer materials science, engineering and manufacturing promote economic growth and benefit society. Polymer nanofibers have widespread applications in a variety of critical industries including energy, transportation, aerospace, healthcare, electronics and sensing. Theoretically, nanofibers are expected to be stronger than larger conventional fibers, but in practice nanofibers are usually much weaker. This discrepancy arises because the manufacturing processes required to engineer ordered internal structures are difficult to apply to tiny, delicate nanofibers. This grant supports the investigation of fundamental scientific relationships associated with laser heating during polymer nanofiber stretching for exceptional control over the internal structure and resulting enhanced strength. Furthermore, the research uses a unique automated track continuous fiber-drawing system that ensures scale up and a clear path to commercialization. The project provides advanced training in materials science, advanced manufacturing and nanotechnology to numerous undergraduate and graduate students and establishes the Path to BS Research Training Program that supports underrepresented, economically disadvantaged students seeking BS degrees in Engineering.Laser zone drawing has demonstrated the potential to produce polymer fibers with high tensile strengths that exceed what is possible using conventional fiber manufacturing methods. However, the fundamental thermodynamic and material processing relationships governing laser zone fiber drawing have not been studied under tightly controlled conditions, especially for polymer nanofibers. This work fills that knowledge gap by using computational models and experimental investigation of polymer fibers subject to laser heating while the mechanical properties are continuously monitored. To process entire fibers, the laser beam is sequentially scanned to rapidly heat each small portion or zone of a fiber to make it pliable so it can be stretched. Macromolecular structure development during laser zone drawing is investigated with known fiber tension and temporal zone temperature. This approach is expected to facilitate remarkable control over the final internal structure of the processed fiber and result in exceptional mechanical strength. The utilization of automated tracks allows for controlled laser zone drawing of the delicate nanofibers. The hypothesis to be tested is that the rapid heating and cooling of nanofibers, due to their high surface area-to-volume ratio, facilitates alignment of polymer chains at elevated temperatures that are locked in place during rapid cooling before chain relaxation can occur, thereby enhancing mechanical behavior.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.