Electro-Collapse Jetting: Towards the Next Generation of Printing Technologies

喷射或液滴形式的小尺寸液体的产生在许多层面上对我们的日常生活产生了重大影响。当对从喷嘴形成的液体弯月面施加电场时，电荷聚集在液体表面上产生应力。这种电力驱动的应力将半月面变形成称为泰勒锥的锥形，由于尖端的奇异性，产生了尺寸比喷嘴小得多的细小射流(电射流)。然后，由于瑞利不稳定性，这种喷流会分解成液滴。由于它在各种技术应用中的应用，如电喷雾质谱学和电流体动力学印刷，了解这一现象的物理机制一直是科学家和工程师关注的焦点。自由液体表面的空穴坍塌是另一个有趣的现象，在这种现象中，动量聚焦等效应会导致产生微小的液滴和气溶胶。这一现象已被用于废水处理、微流体药物输送、作物喷雾和喷墨打印等应用。虽然上述两种现象都会产生小液滴，但每一种现象都有局限性，使其无法产生亚微米级的高粘度和高密度的复杂液体液滴。然后，我们的建议旨在首次全面研究空腔坍塌喷射和电喷射的行为，以深入了解当这两种现象结合时出现的微滴的动力学。这将使我们能够在整个研究过程中获得的知识基础上开发一种新的打印技术。我们还将根据操作条件和液体的物理性质开发一个预测液滴大小和速度的理论模型。该项目的最终目标是使用所提出的打印方法来制造高性能的压电器件，以证明该技术的适用性和有效性。目前可用的液滴生成技术可以产生与喷嘴大小相当的液滴。小而薄的喷嘴更容易堵塞和断裂，制造起来也更困难。这阻碍了这些技术在各种应用中的实施，在这些应用中，需要高颗粒负载油墨(&gt；5000 CP)的高分辨率打印。本项目旨在通过提出一种新的技术来解决这一问题，该技术能够打印小尺寸(&lt；1微米)的高粘性功能材料，超越了市场上当前打印系统提供的尺寸和材料范围。初步数据显示，新技术可以产生尺寸比喷嘴小100倍的喷嘴(不需要小喷嘴)，打印频率比传统的自然电喷脉冲技术(快速打印)高一个数量级。该系统还为非导电表面的电喷问题提供了一种解决方案。在非导电表面上沉积具有相同极性的后续带电液滴是有问题的，因为这会在液滴之间产生排斥力，导致飞溅，从而导致糟糕的印刷。这是因为非导电表面不允许液滴内的电荷消散。然而，拟议系统的灵活性可以使我们中和后续液滴的电荷，这将解决问题并确保即使在非导电表面也能实现高分辨率打印。这将推动高分辨率印刷电子、沉积液晶微/纳米液滴制造微透镜等应用的实现，以及许多依赖于打印复杂流体和高分辨率活性材料的应用，如组织和器官的添加剂制造。

The generation of small sizes of liquids in forms of jets or droplets has a significant impact on our daily life in many levels. When an electric field is applied to a liquid meniscus formed out of a nozzle, electric charges are accumulated on the liquid surface producing stress. This electrically-driven stress deforms the meniscus into a cone shape known as Taylor cone and due to the singularity at the apex, a fine jet, much smaller than the nozzle in size is produced (electrojetting). This jet then breaks up into droplets due to Rayleigh instability. Understanding the physical mechanisms of this phenomenon has been the focus of scientists and engineers due to its use in a variety of technical applications, such as electrospray mass spectrometry and electro-hydrodynamic printing. The collapse of cavities on free liquid surfaces is another interesting phenomenon, in which effects such as momentum focusing can lead to the production of diminutive droplets and aerosols. This phenomenon has been exploited in applications such as wastewater treatment, drug delivery in microfluidics, crop spraying and inkjet printing. While both phenomena described above produce small droplets, each one of these has limitations that prevent it from producing submicron droplets of complex fluids with high viscosity and density. Our proposal then aims to comprehensively study, for the first time, the behavior of both cavity collapse jetting and electrojetting to provide deep insights into the dynamics of the micro-droplets emerged when both phenomena are combined. This would then allow us to develop a novel printing technique based on the knowledge acquired throughout our study. We will also develop a predictive theoretical model for the droplet size and its speed based on the operation conditions and the physical properties of the liquids. The ultimate goal of the project is to use the proposed printing method to fabricate high performance piezoelectric devices as evidence of the applicability and the effectiveness of the technique.The current available droplets generation techniques can produce droplets comparable to the nozzle size. Small and thin nozzles are more prone to clogging and breaking and more difficult to manufacture. This has hindered the implementation of these technologies in a variety of applications, in which the high-resolution printing of highly particle-loaded inks (>5000 cP) is required. This project aims to solve this problem by proposing a novel technique that capable of printing highly viscous functional materials with small sizes (< 1 micron), surpassing the range of sizes and materials offered by the current printing systems in the market. A preliminary data shows that the new technique can produce jets that are up to 100 times smaller than the nozzle in size (no need for small nozzles) and printing frequency that is one order of magnitude higher than the traditional natural electrojetting pulsation technique (fast printing). The proposed system offers also a solution to the problem of electrojetting on non-conductive surfaces. Depositing subsequent charged drops with the same polarity on nonconductive surfaces is problematic because this creates a repulsion force between the droplets leading to splashing and hence poor printing. This is because the nonconductive surface does not permit the charges within the drops to dissipate. However, the flexibility of the proposed system could allow us to neutralize the charges of the subsequent droplets, which will solve the problem and ensure high-resolution printing even on non-conductive surfaces. This will push forward the implementation on applications such as high-resolution printed electronics, manufacturing microlenses by depositing liquid crystals micro/nano droplets and many other applications that depends on printing complex fluids and active materials with high resolution such as additive manufacturing of tissues and organs.