Patterning of Nanofibers on Three-Dimensional Surfaces Using Self-Aligning Nanojets Driven by Electrostatic Forces

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This grant supports research that generates new knowledge in electrospun nanofiber generation and patterning. Nanofibers have high surface area-to-volume ratios and can exhibit multiple functionalities such as piezoelectric energy harvesting and high-sensitivity gas sensing. A variety of applications, e.g., nanocomposites, have been made possible by the random deposition of electrospun nanofibers. Recent efforts in the study of electrospun fibers are driven by a need for programmable patterning of nanofibers. However, current electrospinning processes are not capable of precisely controlling the jet speed and jet angle to achieve programmable patterning, especially, on three-dimensional surfaces. This project studies a novel process to generate a nanometer-scale jet. This nanojet is dominated by the electrostatic force on its surface, which automatically aligns it and, hence, the nanofiber, along the normal direction of the three-dimensional surface. This feature enables the precise deposition of nanofibers, which is beneficial for various emerging applications such as flexible and wearable electronics and three-dimensional cell and tissue scaffolds. Advancing applications in these areas greatly impacts national economy and prosperity. This study involves various research disciplines including advanced manufacturing, electronics, control, electrohydrodynamics, numerical modeling and material science and, thus, provides multi-disciplinary educational opportunities to students. It also increases the participation of women and underrepresented minorities in research.A self-aligning nanojet (SA-N) can enable precise patterning of functional nanofibers on three-dimensional shapes, such as spherical surfaces and vertical walls. When SA-N is enabled, a micron-scale cone is formed on the surface of the droplet that aligns itself along the maximum electric field formed between the droplet and the collector surface. This unique property of SA-N requires a different approach when understanding the governing force and stress acting on the jet in which gravity, inertia and volumetric flow no longer govern the behavior of the jet. Unlike conventional electrospinning, in SA-N, the effect of surface current on the jet becomes more prominent compared to convective and conductive currents. The research team plans to perform multi-physics modeling by incorporating level-set method on the electrohydrodynamic phenomenon occurring in SA-N and experiments to test the hypothesis that the surface current induced electrostatic force on the SA-N surface is significantly greater than the hydrodynamic and gravitational forces, and hence dominate the direction and speed of SA-N. Vision-based monitoring and real-time control of applied voltage and droplet size are implemented to continuously match the jet speed with the stage translation speed, while a 3D rendering tool is exploited to generate the syringe moving path.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.