Rapid mixing of viscous liquids by electrical coiling

Abstract

The control for the processing of precursor liquids determines whether the properties and functions of the final material product can be engineered. An inherent challenge of processing viscous liquids arises from their large resistance to deform. Here, we report on the discovery of an electric approach that can significantly contribute to address this challenge. The applied electric force can induce a straight viscous jet to coil, and the resulting coiling characteristics are governed by the electric stress. We demonstrate the promising use of electrical coiling in the rapid and efficient mixing of viscous liquids. Remarkably, the degree of mixing can be precisely adjusted by tuning the applied electric stress. Our approach of controlling the coiling electrically has important implications on applications such as dispensing and printing of resins, printing patterned surfaces and scaffolds, processing of food and generating non-woven fabrics.

Nanofluidic Behaviors of Water and Ions in Covalent Triazine Framework (CTF) Multilayers

“…The behavior of fluids in such tight confinement may qualitatively differ from that in bulk spaces because the parameters of surface tension, energy dissipation as well as the interaction of fluids with channel walls start to significantly influence the transport process . Understanding the nanofluidic behaviors of fluids inside confined spaces will help to enhance the device performances and also to design new devices in which fluid transport plays a key role . As one of the typical applications of nanofluidics, membrane separation, for example, ultrafiltration, nanofiltration, and reverse osmosis, is the process of fluids passing through the confinement of membrane pores (typically smaller than 100 nm) while components in fluids exhibit their own distinct transport behaviors .…”

Facile Control of Liquid-Rope Coiling With Tunable Electric Field Configuration

“…As an electric field can suppress the Rayleigh-Plateau instability completely for a viscous jet in air [6][7][8], the liquid thread can be deposited onto a substrate continuously without breaking up to achieve a diameter of a filament hundreds of times smaller than that of the nozzle size [9]. A charged jet can manifest a coiling behavior in the presence of an electric field under appropriate operating conditions [10,11], because it is an intrinsic tendency for a significantly thinned and accelerated liquid thread to buckle, bend, and coil, which is commonly termed as liquid-rope coiling [12,13], which contains rich dynamics [14][15][16] and applications [17][18][19][20]. Unlike the spontaneous coiling that can only happen above a critical dispensing height, which allows the jet to get sufficiently thinned and accelerated [21][22][23], the minimum dispensing distance to trigger coiling for a charged jet and the result * ashum@hku.hk jet diameter can be significantly scaled down compared to an uncharged jet.…”

“…Unlike the spontaneous coiling that can only happen above a critical dispensing height, which allows the jet to get sufficiently thinned and accelerated [21][22][23], the minimum dispensing distance to trigger coiling for a charged jet and the result * ashum@hku.hk jet diameter can be significantly scaled down compared to an uncharged jet. This approach has been exploited to print patterns of fibers with improved resolution to as fine as hundreds of nanometers [24] or to handle viscous fluids, which are usually cumbersome to manipulate due to their sticky and thick natures [10]. Besides electric coiling, other techniques such as electrospinning [5,[25][26][27] or electrospray [28,30], where tiny liquid threads and droplets are formed under electric charging, can also be induced under appropriate operating conditions for material synthesis or engineering of functional structures.…”

Bioinspired Helical Microfibers from Microfluidics

“…Microfibers with controllable sizes and morphologies could also be generated continuously using coflow microfluidic approaches. These microfibers have found important applications in many different areas . However, the recent approaches to microfluidics cannot generate helical microfibers with complex morphologies and tunable compositions, and the potential value of the helical microfibers for biomedical engineering remains unexplored.…”