Replicating and Resolving Wetting and Adhesion Characteristics of a Rose Petal

Publication date: Available online 15 October 2018Source: Colloids and Surfaces A: Physicochemical and Engineering AspectsAuthor(s): Udita Uday Ghosh, Sachin Nair, Anuja Das, Rabibrata Mukherjee, Sunando DasGuptaAbstractA Rose petal is well known for a unique form of hydrophobicity, exhibiting simultaneously high apparent equilibrium contact angle (θ*) as well as high adhesion that hinders the rolling off of droplets. This behaviour is fundamentally different than that commonly encountered in other bio-mimetic superhydrophobic surfaces (like a lotus leaf) that have air entrapped in th esolid-liquid contact zone (Cassie Baxter wetting state), thereby exhibiting low adhesion. Based on laser scanning confocal microscopy as well as underwater in-situ atomic force microscopy, we obtain high resolution image of the water-substrate contact region (~ 0.9 – 20 µm) which is significantly higher than that reported so far in the literature. We clearly demonstrate that this unique "Petal effect" can indeed be attributed to the Cassie impregnating wetting state, thereby resolving the prevailing ambiguity on this topic. We have also replicated the structure of the actual rose petals using soft lithography on cross-linked polydimethylsiloxane (PDMS, Sylgard 184) and show that both θ* as well as the adhesive properties of the replicated surface to be nearly identical to that of an actual petal. This implies that the force of adhesion depends on the wetting state and the area of contact...
Source: Colloids and Surfaces A: Physicochemical and Engineering Aspects - Category: Chemistry Source Type: research