Evaporation of Sessile Droplets on Slippery Liquid-Infused Porous Surfaces (SLIPS)

Abstract

Over the past decade, the most common approach to creating liquid shedding surfaces has been to amplify the effects of nonwetting surface chemistry, using micro/ nanotexturing to create superhydrophobic and superoleophobic surfaces. Recently, an alternative approach using impregnation of micro/nanotextured surfaces with immiscible lubricating liquids to create slippery liquid-infused porous surfaces (SLIPS) has been developed. These types of surfaces open up new opportunities to study the mechanism of evaporation of sessile droplets in zero contact angle hysteresis situations where the contact line is completely mobile. In this study, we fabricated surfaces consisting of square pillars (10−90 μm) of SU-8 photoresist arranged in square lattice patterns with the center-to-center separation between pillars of 100 μm, on which a hydrophobic coating was deposited and the textures impregnated by a lubricating silicone oil. These surfaces showed generally low sliding angles of 1°or less for small droplets of water. Droplet profiles were more complicated than on nonimpregnated surfaces and displayed a spherical cap shape modified by a wetting ridge close to the contact line due to balancing the interfacial forces at the line of contact between the droplet, the lubricant liquid and air (represented by a Neumann triangle). The wetting ridge leads to the concept of a wetting "skirt" of lubricant around the base of the droplet. For the SLIP surfaces, we found that the evaporation of small sessile droplets (∼2 mm in diameter) followed an ideal constant contact angle mode where the apparent contact angle was defined from the intersection of the substrate profile with the droplet spherical cap profile. A theoretical model based on diffusion controlled evaporation was able to predict a linear dependence in time for the square of the apparent contact radius. The experimental data was in excellent quantitative agreement with the theory and enabled estimates of the diffusion constant to be obtained.

Slippery Liquid-Infused Porous Surfaces and Droplet Transportation by Surface Acoustic Waves

“…In our previous work on droplet evaporation from SLIPS surfaces, we have observed that a droplet will inherently have a very low contact angle hysteresis [37] and be highly mobile, typically moving when a surface is tilted from the horizontal by less than 1 o , due to the existence of the lubricating layer. Ensuring conditions in eq.…”

“…In the present work, we propose a new method for SAW-induced droplet actuation, which is built on our understanding of SLIP surfaces [22,33,34,37,38]. In our case the infused liquid is chosen to be a lubricant oil and by designing the SLIP surface layer to be significantly thinner than the SAW wavelength, we ensure that little damping of the acoustic wave occurs by the lubricant in the SLIP layer.…”

Grafting of amphiphilic block copolymers on lignocellulosic materials via SI‐AGET‐ATRP

“…145°) is observed. The decrease of CA over time in the case of pure POFPMA is likely due to the evaporation of the water drop …”

Emerging Applications of Bioinspired Slippery Surfaces in Biomedical Fields

“…Beyond antibiofouling and antithrombosis of medical devices/materials, slippery surface were applied to enhance the sensitivity of Raman scattering detection . It is well noted that LISS allow a constant contact angle evaporation (contact line pinning‐free evaporation) because of the high mobility and low hysteresis of the apparent contact line . By using slippery surface as a platform to enrich and delivery to molar level solutions (Figure ), researchers demonstrated ultrasensitive detection (down to the subfemtomolar level (<10 −15 mol L −1 )) of chemical and biological molecules (e.g.…”

“…[15c] It is welln oted that LISS allow ac onstant contact angle evaporation (contact line pinning-free evaporation)b ecause of the high mobility and low hysteresis of the apparent contact line. [55] By using slippery surface as ap latform to enrich and delivery to molar level solutions (Figure 12), researchers demonstrated ultrasensitive detection (down to the subfemtomolar level (< 10 À15 mol L À1 )) of chemical and biological molecules (e.g. thymine, adenine and BSA) and environmental contaminants in different fluids throughs lippery surface enhanced Ramans cattering and molecular sensing.…”