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

这笔拨款支持在电纺纳米纤维的产生和图案化方面产生新知识的研究。纳米纤维具有很高的比表面积与体积比，可以表现出多种功能，如收集压电能量和高灵敏度的气体传感。通过电纺纳米纤维的随机沉积，已经使得各种应用成为可能，例如纳米复合材料。最近研究电纺纤维的努力是由对纳米纤维的可编程图案化的需求推动的。然而，目前的电纺工艺不能精确地控制喷射速度和喷射角度来实现可编程的图案化，特别是在三维表面上。该项目研究了一种产生纳米级射流的新工艺。这种纳米射流是由其表面的静电力控制的，这会自动使它和纳米纤维沿着三维表面的法线方向对齐。这一特性使纳米纤维能够精确沉积，这有利于各种新兴应用，如柔性和可穿戴的电子设备以及三维细胞和组织支架。推进这些领域的应用将极大地影响国民经济和繁荣。这项研究涉及多个研究学科，包括先进制造、电子学、控制、电流体力学、数值模拟和材料科学，因此为学生提供了多学科的教育机会。它还增加了妇女和代表性不足的少数群体参与研究的机会。自对准纳米射流(SA-N)可以在球面和垂直墙壁等三维形状上精确绘制功能纳米纤维的图案。当启用SA-N时，液滴表面会形成一个微米级的锥体，该锥体沿液滴和收集器表面之间形成的最大电场对齐。SA-N的这一独特特性需要不同的方法来理解作用在射流上的控制力和应力，在这种情况下，重力、惯性和体积流不再主导射流的行为。与传统的电纺不同，在SA-N中，与对流和传导电流相比，表面电流对射流的影响变得更加突出。研究小组计划通过结合水平集方法对SA-N中发生的电流体动力学现象进行多物理建模，并通过实验验证表面电流在SA-N表面诱导的静电力明显大于流体动力和重力的假设，从而主导SA-N的方向和速度。实施了基于视觉的监测和应用电压和液滴大小的实时控制，以持续匹配喷射速度和舞台平移速度，同时利用3D渲染工具生成注射器移动路径。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.