School of Materials Science & Engineering, Clemson University, 161 Sirrine Hall, Clemson, South Carolina 29634, United States.
Langmuir. 2011 Mar 15;27(6):3206-10. doi: 10.1021/la104855b. Epub 2011 Feb 20.
Many engineering applications assume the generation of single spherical droplets on demand. Piezo and thermo droplet-on-demand (DOD) instruments are not able to produce droplets with a broad range of size distributions from the same nozzle. We show that this challenge can be resolved using the principles of electrostatic generation and capillarity. A thin conductive wire threaded through a needle can be used as the droplet electrogenerator (or DOD generator). By applying a weak-bias electric field, one can deliver a drop from the needle edge to the free wire tip. When the drop moves toward the wire tip, it leaves behind a thin coating film. The capillary pressure of this cylindrical film helps isolate the droplet from the liquid source: the film spontaneously thins, breaking the connection between the droplet and the liquid source. The detachment of a pendant drop from the wire is then achieved by applying a short voltage pulse. Using the wire-in-a-needle nozzle, we were able to produce single droplets ranging from 50 to 500 μm, and we were able to deposit them with controlled velocity in a prescribed position. Therefore, the proposed method offers new opportunities in fields dealing with the DOD applications.
许多工程应用都假设能够按需生成单个球形液滴。压电和热式按需（DOD）仪器无法从同一喷嘴产生具有广泛尺寸分布的液滴。我们表明，使用静电生成和毛细作用的原理可以解决这一挑战。一根细的导电丝穿过一根针，可以用作液滴发生器（或 DOD 发生器）。通过施加弱偏置电场，可以将液滴从针的边缘输送到自由的丝尖。当液滴向丝尖移动时，它会在后面留下一层很薄的涂层。该圆柱形薄膜的毛细压力有助于将液滴与液体源隔离：薄膜会自动变薄，从而切断液滴与液体源之间的连接。然后，通过施加短电压脉冲，就可以实现从丝上悬挂液滴的脱离。使用针内丝喷嘴，我们能够产生 50 到 500 微米的单个液滴，并能够以受控的速度将它们沉积在预定位置。因此，该方法为涉及 DOD 应用的领域提供了新的机会。
