Tunable lotus-leaf and rose-petal effects via graphene paper origami

Whereas water drops on both lotus leafs and rose petals have high contact angles, the drops can easily roll off lotus leafs but strongly adhere to rose petals. Here, we report a simple and cost-effective approach to fabricate highly stretchable large-area surfaces that give lotusleaf and rose-petal effects by harnessing origami patterns formed in graphene paper (GP) bonded on a pre-strained elastomer substrate. The surfaces of the GP origami exhibit high contact angles (>160 degrees) yet robust adhesion to water drops. After depositing a gold film of a few nanometers on the GP, the origami of GP-Au gives high contact angle (>160 degrees) and low roll-off angles (< 5 degrees) of water drops. We show that the high surface roughness of the GP origami leads to the high contact angle of water drops, and hydrophilic groups and defects on the GP surface significantly enhance the adhesive forces of drops on the GP origami, leading to the rose-petal effect. The coating of gold film does not affect the surface roughness of the origami but significantly reduces the adhesive force, transitioning the rose-petal to lotus-leaf effects. In addition, the wetting properties of both GP and GP-Au origamis can be tuned over a wide range by simply stretching or compressing the substrate elastomer. (C) 2015 Elsevier Ltd. All rights reserved.