Droplet evaporation on superhydrophobic surfaces

Abstract

Over the last decades, a fabulous variety of synthetic superhydrophobic surfaces have been created, offering unique anti-wetting properties. A significant focus for these surfaces has been on their stay-dry and self-cleaning properties. However, unless in a saturated environment, water droplets lose mass through evaporation and this itself is a field of significant interest, which is illustrated by a flood of recent studies on surface contamination and potential surface transmission of infection by evaporating sessile droplets during the Covid-19 pandemic. Superhydrophobic surfaces alter a droplet's contact with a substrate and the surrounding environment, thus changing pinning and heat transfer properties. The droplet shape also alters the space into which vapor can diffuse. Despite the many excellent reviews on superhydrophobic surfaces, there does not appear to have been a focus on the overlap with evaporating sessile droplets. Here, we address this gap by outlining the diffusion-limited sessile droplet evaporation theory, applications on patterned superhydrophobic surfaces, effect of evaporative cooling on drop evaporation rates, and practical applications of drop evaporation on superhydrophobic surfaces, such as nanoparticle assembly, biomedical assay, analytical chemistry, and crystallization applications. Finally, we provide our personal views of possible future directions in these overlapping areas.

The fractal geometry of polymeric materials surfaces: surface area and fractal length scales

“…ref. 42 and 80), specifically in the way the fractal scaling is treated and in the consistency relationship between the fractal dimension and the effective surface area of the polymeric samples.…”

Fundamentals and Applications of Surface Wetting

“…204 The evaporation of sessile droplets on such surfaces has also been characterized recently. 205,206 More detailed reviews of distinct aspects of sessile droplet evaporation can be found elsewhere, such as evaporation on superhydrophobic substrates, 207 and an analytical description of the process. 208 In addition to well-studied contact line dynamics, the solid− liquid interaction during evaporation affects thermal and internal flow fields.…”

“…Similarly, evaporation of sessile droplets is also analyzed on soft viscoelastic surfaces, , where, for instance, a deformation near the contact line can impact the wetting transition affecting the overall evaporation process. , Interestingly, in an effort to battle the COVID-19 pandemic, the viability of virus-laden droplets on different surfaces is also studied using droplet evaporation as the primary fundamental mechanism. , With the ongoing research efforts to create surfaces with unique wetting properties, biphilic substrates also have gained attention . The evaporation of sessile droplets on such surfaces has also been characterized recently. , More detailed reviews of distinct aspects of sessile droplet evaporation can be found elsewhere, such as evaporation on superhydrophobic substrates, and an analytical description of the process …”

Numerical Analysis of the Dispersion and Deposition of Particles in Evaporating Sessile Droplets

“…The combination of these features makes evaporating sessile droplets with dispersed particles an intriguing and challenging topic for research. Recently, intense research has been conducted on this topic as suggested by the number and the quality of reviews and books published in the past decade. − …”