378840 Observation of Rose Petal Effect on Single Microscale or Nanoscale Roughness Surfaces
In 2008, Jiang and coworkers  pointed out that the rose petals possess the characteristic of super-hydrophobicity with strong adhesion to pin water drops. This phenomenon is well known as “petal effect”. It is generally believed that the petal effect is attributed to dual scale roughness and the water droplet can penetrate into the micro-scale roughness but not the nano-scale roughness. In this study, a surface of the single scale (either micro-scale or nano-scale) roughness within certain roughness region is observed to exhibit petal effect. A series of micro- and nano-pillar-like patterned surfaces with different roughnesses are fabricated. The advancing/receding contact angles and sliding angle of a water droplet on these patterned surfaces are carefully measured. When the surface roughness is increased and carefully tuned, a patterned surface of petal effect is consistently observed. That is, the dual-scale roughness is not a necessary condition for a surface of petal effect. Simulation results of the metastable states of a liquid droplet deposited on a hydrophobic sinusoidal surface by using the Surface Evolver [2,3] are discussed and applied to support the viewpoint that single scale roughness surface could exhibit the petal effect.
1. L. Feng, Y. N. Zhang, J. M. Xi, Y. Zhu, N. Wang, F. Xia and L. Jiang, Langmuir 2008, 24, 4114–4119.
2. A. Promraksa and L. J. Chen, J. Colloids Interfacial Sci. 2012, 384, 172-181.
3. A. Promraksa, Y. C. Chuang and L. J. Chen, J. Colloids Interfacial Sci. 2014, 418, 8-19.