Electro-coiling of liquid jets

Abstract

Interactions of fluid-fluid interfaces with electrical charging has led to a variety of dynamic phenomena and applications. For instance, the charging of a liquid jet can reduce its diameter, resulting in a whipping of the jet that is often used as a template to form nano-structured substrates for tissue engineering; the breakup of electrified jet can also led to small droplets that are used as templates for forming micro-particles. Recently, viscous liquid jets have also been shown to exhibit coiling dynamics, where the coiling frequency and the jet diameter can be conveniently controlled, offering enhanced degree of control in comparison to the traditional liquid rope coiling. In all of these processes, the viscous, electrostatic and surface tension stresses interplay intricately; a comprehensive understanding that connects the often-observed phenomena of jetting, coiling and whipping would be crucial for enhancing the performance of the liquid-jet-based applications. However, the narrow window of the operating parameters, such as the viscosity, electric field and surface tension, has limited the observation of all three phenomena within the same liquid system. In this talk, I will introduce a liquid-liquid system with a low interfacial tension and demonstrate that transitions among the three regimes can be studied, enabling elucidation of the underlying mechanisms. In addition, based on the understanding, we integrate the electro-coiling phenomenon into a translation stage to achieve versatile printing of curved filaments. The electro-coiling can guide the printing of multiscale architectures; as the coding path and the deposited ink-line can be decoupled, the spatiotemporal resolution can be increased. In particular, as the coiling patterns, including straight line, meandering line, alternating loops, and translated coils, are highly sensitive to the electrical conditions, which can be varied conveniently, switching of patterns can be completed within a single wavelength. The electric field also helps to reduce the jet diameter down to the nanometer range; thus nanometersized curved patterns can be printed, representing a 100-fold improvement from existing inertial-coiling techniques. The electro-coiling-guided printing of a centimetersized architectures of nanofibers can be completed within a few minutes using a single liquid jet. The increase in printing speed and resolution creates exciting opportunities for applications that derive their functions from the architectures of the fiber networks, such as those with spatially programmable mechanical properties.