In Situ Reversible Control between Sliding and Pinning for Diverse Liquids under Ultra-Low Voltage

Abstract

Thermally responsive paraffin-infused slippery surfaces have demonstrated intriguing performance in manipulating the behaviors of versatile droplets. However, present methods have been limited to ex situ rigid heat sources with a high voltage of 220 V or certain specific photothermal materials, which greatly hinders its practical applications. To solve this problem, an intelligent droplet motion control actuator (DMCA) composed of paraffin wax, hydrophobic micropillar-arrayed ZnO film, and a flexible transparent silver nanowire heater (SNWH) is reported in this work. Due to the good portability of DMCA, in situ switchable wettability for several liquid droplets with different surface tensions can be achieved by simply loading and unloading Joule heat at an ultra-low voltage (12 V). The relationship among sliding velocity and droplet volume and inclined angles was quantitatively investigated. By virtue of the flexible and mechanical endurance, this smart DMCA is dramatically functional for droplet motion manipulation (e.g., reversible control between sliding and pinning) on complex 3D surfaces. Significantly, an impressive self-healing ability within 22 s is also demonstrated through the in situ application of Joule heat on the scratched DMCA, which renders its practical usability in various harsh conditions. This work provides insights for designing intelligent, flexible, and portable actuators dealing with the challenges of smart temperature-responsive surfaces.

A Review of Smart Lubricant-Infused Surfaces for Droplet Manipulation

“…By tilting the LIS, the droplet can slide along the fluid pathway [41]. This technique was improved by integrating a flexible silver nanowire heater with the paraffin-infused micropillar-arrayed zinc oxide LIS [38]. By loading a 12 V voltage on the nanowires, the paraffin becomes melting, with the interface transition from an air-liquid-liquid to a lubricated air-liquid-solid one within 40 s.…”

“…Targeting this active direction, Yang et al summarized developments of wettability-tunable LISs induced by external stimuli and their applications in fog collection, oil-water separation, complex-flow distribution, droplets' delivery in 2019 [37]. However, with the fast advancement of smart LISs, many important and successive works on improvements of responsive LISs and other nonconventional LISs were developed for droplet manipulation [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55], but these studies are not reported by Yang' work. This review is an overview of the recent progress in smart LIS for droplet manipulation induced by external stimuli, as presented in Figure 1. We first give a summary of some unique properties and fundamentals of droplets on LIS.…”

Design Principles for Aqueous Interactive Materials: Lessons from Small Molecules and Stimuli‐Responsive Systems

“…Several attempts have been made to switch between the two states, mainly by manipulating the surface topology using an electrical or magnetic field 120,121. Only two recent publications highlight the use of stretchable surfaces, which show remarkable interactions with water and can be considered as mechanoresponsive materials.…”

Slippery liquid‐infused porous surface via thermally induced phase separation for enhanced corrosion protection

“…Slippery liquid-infused porous surface (SLIPS), as an emerging surface inspired by Nepenthes pitcher plant, has attracted widespread interest in diverse application fields such as self-cleaning, [1][2][3][4] liquid manipulation, [5][6][7][8][9] anti-biofouling, [10][11][12] anti-icing, [13][14][15] anti-corrosion, [16][17][18][19] and so on. SLIPS refers to a dynamic surface composed of a macro-or nano-structured porous substrate infused with a lubricant fluid, normally immiscible with water.…”