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

这项拨款支持在静电纺纳米纤维生成和图案方面产生新知识的研究。纳米纤维具有较高的表面积体积比，具有压电能量收集和高灵敏度气体传感等多种功能。静电纺纳米纤维的随机沉积使纳米复合材料等多种应用成为可能。对纳米纤维可编程图案的需求推动了电纺丝纤维的研究。然而，目前的静电纺丝工艺不能精确控制喷射速度和喷射角度来实现可编程的图案，特别是在三维表面上。本项目研究了一种产生纳米尺度射流的新工艺。这种纳米射流受其表面上的静电力支配，静电力会自动使纳米射流和纳米纤维沿着三维表面的法线方向排列。这一特性使纳米纤维的精确沉积成为可能，有利于各种新兴应用，如柔性和可穿戴电子产品以及三维细胞和组织支架。这些领域的应用的推进对国民经济和繁荣有着重要的影响。本专业涉及先进制造、电子学、控制学、电流体力学、数值模拟和材料科学等多个学科，为学生提供多学科的教育机会。它还增加了妇女和代表性不足的少数民族对研究的参与。自对准纳米射流（SA-N）可以在三维形状（如球面和垂直壁）上实现功能纳米纤维的精确图像化。当SA-N被启用时，在液滴表面形成一个微米尺度的锥体，该锥体沿着液滴和集热器表面之间形成的最大电场排列。SA-N的这种独特性质要求我们在理解作用在射流上的控制力和应力时采用不同的方法，在这种情况下，重力、惯性和体积流不再控制射流的行为。与传统的静电纺丝不同，在SA-N中，与对流和导电电流相比，表面电流对射流的影响更加突出。课题组计划采用水平集方法对SA-N中发生的电流体动力现象进行多物理场建模，并通过实验验证表面电流对SA-N表面产生的静电力明显大于水动力和重力，从而支配SA-N的方向和速度的假设。基于视觉的监测和实时控制施加电压和液滴大小，以持续匹配喷射速度和工作台平移速度，同时利用3D渲染工具生成注射器移动路径。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.