Abstract
Liquid marbles (LMs) have many promising roles in the ongoing development of microfluidics, microreactors, bioreactors, and unconventional computing. In many of these applications, the coalescence of two LMs is either required or actively discouraged, therefore it is important to study liquid marble collisions and establish parameters which enable the desired collision outcome. Recent reports on LM coalescence have focused on either two mobile LMs colliding, or an accelerating LM hitting a sessile LM with a backstop. A further possible scenario is the impact of a mobile LM against a non-supported static LM. This paper investigates such a collision, using high-speed videography for single-frame analysis. Multiple collisions were undertaken whilst varying the modified Weber number (We*) and offset ratios (X*). Parameter ranges of 1.0 < We* < 1.4 and 0.0 < X* < 0.1, resulted in a coalescence rate of approximately 50%. Whereas, parameter ranges X* > 0.25, and We* < 0.95 or We* > 1.55 resulted in 100% non-coalescence. Additionally, observations of LMs moving above a threshold velocity of 0.6 m s-1 have revealed a new and unusual deformation. Comparisons of the outcome of collisions whilst varying both the LM volume and the powder grain size have also been made, revealing a strong link. The results of this work provide a deeper understanding of LM coalescence, allowing improved control when designing future collision experiments.
Highlights
Liquid marbles (LMs) consist of tiny droplets of liquid, coated in a hydrophobic powder
Whilst there was variation in the non-coalescing events, all impacts that did result in coalescence followed the same pathway, as demonstrated in Fig. 6, and in the video available in the Electronic supplementary information (ESI).† As the approaching LM nears the static LM, it is travelling at high speed (n 4 0.5 m sÀ1) and with a small offset ratio
It was shown that for a PE LM with a volume of 15 mL at optimal collision conditions (1.0 o Weber number (We)* o 1.4 and 0.0 o X* o 0.1), the occurrence of coalescence was no greater than 50%
Summary
Liquid marbles (LMs) consist of tiny droplets of liquid, coated in a hydrophobic powder. Despite the hydrophobic powder barrier, several studies reporting and investigating the coalescence of LMs have been published in recent years.[15,16] The impact resulting from the vertical collision of two LMs has been reported on by Planchette et al.,[17] and more recently by Jin et al in 2018.18 In both cases, a LM was dropped from a known height onto a stationary LM These impacts were monitored by high-speed camera, using individual frames to determine speed and impact behaviour. The potential for use of LMs in microfluidics is growing rapidly,[28] as is their use in micro- and bio-reactors.[10,29] This is because they hold many advantages over more traditional techniques, such as faster kinetics, reduced chemical cost, and discrete encapsulation (eliminating the contamination from the oil phase frequently used in digital microfluidics) In each of these fields coalescence of LMs, in order to mix chemicals, is often required. By considering the size, coating, volume, velocity, Weber number (We), and offset ratio (X*) of these collisions, the parameters required for coalescence were investigated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
