Directed motion of two-component droplets on wedge-shaped composite copper surfaces without back-end pinning
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RESEARCH PAPER
Directed motion of two‑component droplets on wedge‑shaped composite copper surfaces without back‑end pinning Hui Zhang1 · Jiang Cheng1 · Shouping Xu1 · Pihui Pi1 · Xiufang Wen1 · Cailong Zhou2 Received: 30 April 2020 / Accepted: 27 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The motion of three-phase contact line of a droplet is always halted by the contact angle hysteresis on a common solid surface. In this work, the Ag/Cu surface and Cu(OH)2/Cu surface with water contact angle of 25.0° were fabricated and found favorable for two-component droplet moving. The droplet, water with propylene glycol in irregular shape could restore to a circle (top view) on these prepared surfaces. Inspired by the shape restoration, the directed motion of two-component droplet without back-end pinning was achieved on both the wedge-shaped Ag/Cu and Cu(OH)2/Cu composite surfaces. The two-component droplet moves in a way of the front-end spreading with the subsequent back-end shrinking. The needle-like Cu(OH)2 microstructure is more conducive to the front-end spreading, while the spheroidal Ag particles on Cu substrate is in favor of the back-end shrinking. In addition, the segmented Ag@Cu(OH)2/Cu wedge-shaped composite surfaces with Ag film on the narrow end of the track and Cu(OH)2 on the wide end could enhance the droplet moving. Finally, a microchemical reactor was designed capable of driving two dispersed droplets to move in a specific direction, converge, and then react with each other. Keywords Two-component droplet · Shape restoration · Copper · Wedge-shaped composite surface · Directed motion
1 Introduction Droplet manipulation technology in recent years has attracted great interest for promising applications in the fields of heat and mass transfer (Al-Sharafi et al. 2018; Edalatpour et al. 2018), virus detection (Prakash et al. 2013, 2015), and micro-reactor (Song et al. 2019). Lots of efforts have been made to realize the motion of droplet on solid surface through adjusting factors such as chemical concentration (Cira et al. 2015; Man and Doi 2017; Singh et al. 2017), magnetic (Aziz et al. 2018), light (Ichimura et al. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10404-020-02376-w) contains supplementary material, which is available to authorized users. * Jiang Cheng [email protected] 1
School of Chemistry and Chemical Engineering, Guangdong Provincial Key Lab of Green Chemical Product Technology, South China University of Technology, Guangzhou 510640, People’s Republic of China
School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, People’s Republic of China
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2000; Thomas and Unni 2019), and electricity (Mugele 2019; Tian 2016). Droplet motion can also be achieved by patterning the surface to irregular shape which can induce an unbalanced interfacial tension (Alheshibri et al. 2012; Chen 2017; Deng 2017; Katoh et al. 2018; Xu and Chen 2019). However, the contact line pini
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