Lubricant-Mediated Strong Droplet Adhesion on Lubricant-Impregnated Surfaces

Abstract

Lubricant-impregnated surfaces have recently emerged as a new type of multifunctional coating with a promising capability in exhibiting low friction or contact angle hysteresis. However, lubricant-infused surfaces severely suffer from the tensile droplet−lubricant adhesion. In this study, we show that lubricantinfused surfaces allow for a strong tensile droplet adhesion, which results in the generation of an offspring residual droplet when a droplet detaches from the surface. Such tensile liquid−liquid adhesion and the corresponding liquid residue are solely mediated by the lubricant, independent of the underlying surface topography. We reveal how the lubricant film mediates droplet adhesion by measuring the maximum adhesion force and liquid residue and theoretically analyzing Laplace pressure force from the droplet shape and surface tension force depending on the contact line. Further, the presence of lubricant-induced adhesion considerably compromises the advantages of lubricant-infused surfaces in some applications. The lubricant-triggered tensile adhesion hampers the loss-free droplet transfer away from the surfaces in the photoelectrically and magnetically driven droplet manipulation. In addition, we demonstrate that the lubricant-triggered adhesion plays a dominant role in attenuating the efficiency of fog harvesting by impeding the shedding of the intercepted droplets by comparing the onset time, droplet radius, and collection efficiency. These findings advance our fundamental understanding of droplet adhesion on lubricant-infused surfaces and significantly benefit the design of lubricant-infused surfaces for various applications.

Droplet Bouncing: Fundamentals, Regulations, and Applications

“…The droplet bouncing on nonwetting solid surfaces is ubiquitous in nature [16,17] and is important in many industrial processes like spraying, [18] anti-icing, [19][20][21] or self-cleaning. [22] There are three elementary parameters to characterize wetting properties of the solid surface (Figure 2): i) the contact angle θ of the droplet on the solid surface, [23][24][25][26] showing the static wetting property; ii) the contact angle hysteresis CAH = θ advancing -θ receding when droplet moves on the solid surface, [27][28][29][30] being the difference between the advancing angle θ advancing and receding angle θ receding and reflecting the mobility of the droplet on the solid surface; and iii) the sliding angle θ sliding , being the inclined angle of the solid surface when the droplet starts sliding. For droplet bouncing, the nonwetting solid surface typically should possess a high contact angle, a low contact angle hysteresis and a low sliding angle.…”

Non‐Hookean Droplet Spring for Enhancing Hydropower Harvest

“…[ 27 ] To explain the divergent spring behaviors for different‐sized patterns, we investigate the origin of the tensile force generated by the droplet‐based spring. The tensile force is the sum of the Laplace pressure F L (related to the droplet‐solid contact area and the contact angle) and the surface tension F S (related to the length of the TCL and the contact angle), [ 28 ] and the latter is dominant. For small patterns, with the stretching of the spring, the contact angle of the droplet gradually decreases and approaches 90° before break‐up of the liquid bridge, which maintains the increasing trend of the surface tension.…”

Spontaneous Charging of Drops on Lubricant-Infused Surfaces

“…It shows a constant depletion speed of 1.4 nL/drop ±0.3 nL/drop. As schematically shown in Figure b, an annular wetting ridge and a cloaking layer are always formed when water drops slide on the lubricant-infused surfaces. ,, Therefore, the lubricant-depletion may be caused by the cloaking layer and meniscus.…”