Field-Induced Wettability Gradients for No-Loss Transport of Oil Droplets on Slippery Surfaces

Abstract

Transporting oil droplets is crucial for a wide range of industrial and biomedical applications but remains highly challenging due to the large contact angle hysteresis on most solid surfaces. A liquid-infused slippery surface has a low hysteresis contact angle and is a highly promising platform if sufficient wettability gradient can be created. Current strategies used to create wettability gradient typically rely on the engineering of the chemical composition or geometrical structure. However, these strategies are inefficient on a slippery surface because the infused liquid tends to conceal the gradient in the chemical composition and small-scale geometrical structure. Magnifying the structure, on the other hand, will significantly distort the surface topography, which is unwanted in practice.In this study, we address this challenge by introducing a field-induced wettability gradient on a flat slippery surface. By printing radial electrodes array, we can pattern the electric field, which induces gradient contact angles. Theoretical analysis and experimental results reveal that the droplet transport behavior can be captured by a nondimensional electric Bond number. Our surface enables no-loss transport of various types of droplets, which we expect to find important applications such as heat transfer, anticontamination, microfluidics, and biochemical analysis.

Electrothermally Assisted Surface Charge Density Gradient Printing to Drive Droplet Transport

“…Tang et al. established a field-induced wettability gradient strategy to drive an oil droplet on a slippery surface . Unlike previous studies that relied on slippery surfaces with surface-piercing structures, this study eliminated the disadvantage of distorting the macroscopic topography.…”

Recent Growth of Wettability Gradient Surfaces: A Review

“…The achieved wettability gradient on SLI-WGS can better be understood with the help of electrowetting and dielectrowetting theories, stating that the change in contact angles of droplet is proportional to the applied electric potential, which has been practically presented via contact angle (precisely advancing contact angle which is particularly employed for LISs/SLIPSs) reducing from 71.5 °to 52.9 °, evidencing the wide range of wettability gradient in the hydrophilic wetting regime. The water vapor condensation has been examined on SLI-WGS, as shown in Figure 9(f) [84]. It implies that SLI-WGS is the promising candidate to promote the condensation since the water droplets could easily move and were finally collected at the center driven by the wettability gradient.…”

“…A novel approach has been envisioned on stimuli-responsive slippery liquid-infused (SLI) WGS, anticipating the considerable potential of the droplet dynamics induced by electric potential (i.e., substrate tilting is exempted). On the glass substrate [84], ITO-based (indium tin oxide) electrodes at various angles have been radially fabricated via the printing-infusion method, as depicted in Figures 9(a)-9(d). Further, the electrodes are surrounded with polymeric film (polytetrafluoroethylene) with two functions, i.e., insulating the electrodes, as well as creating the porous scaffold into which a slippery liquid (Krytox GPL oil-103) has been impregnated, resulting in electrowetted SLI-WGS.…”

Reliable and Low Temperature Actuation of Water and Oil Slugs in Janus Photothermal Slippery Tube

“…Actuation of liquid droplet or liquid slug is crucial for microfluidic applications. , Many liquid actuation methods have been developed, making use of forces from external stimuli, such as optical, − magnetical, − or electrical forces. , However, most of the research has been focused on the manipulation of droplets on open surfaces. Much less attention has been paid to actuate liquid in closed tubes or channels, despite the fact that most microfluidic applications are performed in microchannels.…”