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

这项资助支持在静电纺丝产生和图案化方面产生新知识的研究。纳米纤维具有高的表面积与体积比，并且可以表现出多种功能，例如压电能量收集和高灵敏度气体传感。各种应用，例如，通过静电纺丝纳米纤维的无规沉积，已经使纳米复合材料成为可能。最近在电纺纤维的研究中的努力是由对纳米纤维的可编程图案化的需要驱动的。然而，目前的静电纺丝工艺不能够精确地控制喷射速度和喷射角度以实现可编程图案化，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方法。该纳米喷射由其表面上的静电力支配，该静电力自动地使其对准，并且因此使纳米喷射沿着三维表面的法线方向对准。这一特性使得纳米纤维的精确沉积成为可能，这对于各种新兴应用都是有益的，例如柔性和可穿戴电子产品以及三维细胞和组织支架。这些领域的应用对国民经济的发展和繁荣有着重要的影响。这项研究涉及各种研究学科，包括先进制造，电子，控制，电流体力学，数值建模和材料科学，因此，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在研究中的参与。自对准纳米喷射（SA-N）可以使功能纳米纤维在三维形状上精确图案化，例如球形表面和垂直壁。当启用SA-N时，在液滴的表面上形成微米级圆锥，其自身沿着在液滴和收集器表面之间形成的最大电场对准。SA-N的这一独特性质要求在理解作用于射流的支配力和应力时采用不同的方法，其中重力、惯性和体积流量不再支配射流的行为。与传统的静电纺丝不同，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，并通过实验来验证表面电流在SA-N表面上引起的静电力明显大于水动力和重力，从而控制SA-N的方向和速度的假设。基于视觉的监控和施加电压和液滴尺寸的实时控制实现了喷射速度与载物台平移速度的连续匹配，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.