High contact angle hysteresis of superhydrophobic surfaces: Hydrophobic defects

Abstract

A typical superhydrophobic surface is essentially nonadhesive and exhibits very low water contact angle (CA) hysteresis, so-called Lotus effect. However, leaves of some plants such as scallion and garlic with an advancing angle exceeding 150° show very serious CA hysteresis. Although surface roughness and epicuticular wax can explain the very high advancing CA, our analysis indicates that the unusual hydrophobic defect, diallyl disulfide, is the key element responsible for contact line pinning on allium leaves. After smearing diallyl disulfide on an extended polytetrafluoroethylene (PTFE) film, which is originally absent of CA hysteresis, the surface remains superhydrophobic but becomes highly adhesive.

Antimicrobial properties of a nanostructured eggshell from a compost-nesting bird

“…However, unlike lotus leaves, brush-turkey eggs have high hysteresis, meaning that the water droplets remain pinned to the surface and thus do not roll off. Similar effects have recently been found in rose petals [the 'petal effect' (Feng et al, 2008)] and other plants (Chang et al, 2009), which the authors attribute to trapping of the water droplet ('Cassie impregnating wetting state') by micropapillae on the surface or hydrophobic chemicals (Chang et al, 2009). The petal effect on brush-turkey shells may trap condensed water at discrete points, preventing it from spreading uniformly over the surface and thereby inhibiting biofilm formation (Shawkey et al, 2009).…”

A simple surface treatment and characterization of AA 6061 aluminum alloy surface for adhesive bonding applications

“…We have previously reported such a Cassie impregnating wetting regime and named it as a "sticky Cassie state" in the case of our ZnO nanotowers where the water drop remained stuck to the surface in spite of very high water contact angles [24]. The rose petal effect has also been widely observed by many other researchers recently [27], [28], [29] and [30]. Since the adhesion of water drops to the surface is higher as defined by the rose petal effect in spite of the higher water contact angle, it may be expected that these surface may exhibit high adhesive bond strength.…”

The rose petal effect and the modes of superhydrophobicity

“…The so-called 'petal effect' is exhibited by a surface that has a high CA, but also a large CA hysteresis and strong adhesion to water. The phenomenon of large CA hysteresis and high water adhesion to rose petals (and similar surfaces), as opposed to small CA hysteresis and low adhesion to lotus leaf, has been observed by several research groups (Bormashenko et al 2009;Chang et al 2009;Bhushan & Her 2010). Bormashenko et al (2009) reported a transition between wetting regimes, e.g.…”

“…It may be useful also to see the transition between the Wenzel, Cassie and dry states as a phase transition, and to add the ability of a surface to bounce off water droplets to the definition of superhydrophobicity (Nosonovsky & Bhushan 2008b). In addition, there is an argument on how the various definitions of CA hysteresis are related to each other (Krasovitski & Marmur 2004;Bormashenko et al 2007Bormashenko et al , 2009Chang et al 2009). …”