Theoretical Explanation of the Lotus Effect: Superhydrophobic Property Changes by Removal of Nanostructures from the Surface of a Lotus Leaf

Abstract

Theoretical study is presented on the wetting behaviors of water droplets over a lotus leaf. Experimental results are interpreted to clarify the trade-offs among the potential energy change, the local pinning energy, and the adhesion energy. The theoretical parameters, calculated from the experimental results, are used to qualitatively explain the relations among surface fractal dimension, surface morphology, and dynamic wetting behaviors. The surface of a lotus leaf, which shows the superhydrophobic lotus effect, was dipped in ethanol to remove the plant waxes. As a result, the lotus effect is lost. The contact angle of a water drop decreased dramatically from 161° of the original surface to 122°. The water droplet was pinned on the surface. From the fractal analysis, the fractal region of the original surface was divided into two regions: a smaller-sized roughness region of 0.3-1.7 μm with D of 1.48 and a region of 1.7-19 μm with D of 1.36. By dipping the leaf in ethanol, the former fractal region, characterized by wax tubes, was lost, and only the latter large fractal region remained. The lotus effect is attributed to a surface structure that is covered with needle-shaped wax tubes, and the remaining surface allows invasion of the water droplet and enlarges the interaction with water.

Postfunctionalization of Azido or Alkyne Poly(3,4‐ethylenedioxythiophene) Surfaces: Superhydrophobic and Parahydrophobic Surfaces

“…[ 14 ] Usually, superhydrophobic properties are obtained by combining high surface roughness (often both of the micro and nanoscale) and low surface energy materials. [ 15,16 ] However, the water adhesion can be controlled by playing with the geometry of the surface structures or by lowering the surface energy. [17][18][19][20] In order to prepare these types of surfaces different approaches can be imagined.…”

Photochromic Crystalline Systems Mimicking Bio‐Functions

“…Recently, it has become possible to control the fine motion of a water droplet by using surface structure . Here, we would like to show that it is possible to understand the water‐bouncing and ‐sliding phenomena based on the model experiments’ characteristic scales of a double‐roughness surface and on simple theory . To estimate this ability, we performed a water‐droplet‐bouncing experiment from a height of 1.8 mm on a diarylethene microcrystalline surface with double‐roughness structures and then compared the results with those of diarylethene with a single‐roughness structure and natural lotus leaf (Figure ).…”

“…The CAs of water droplets on the surfaces in Figure 4, 5, and 6 are 132.5°, 130.4°, and 161.9°, respectively. Only the double‐roughness surface showed super hydrophobicity …”

Nanograting Structured Ultrathin Substrate for Ultraflexible Organic Photovoltaics

“…Nanopatterning onto the surfaces of polymer substrates provides additional functions including the lotus effect and self‐cleaning effect . Among these effects, modified optical characteristics such as the antireflection effect and plasmonics effect are beneficial especially for optical devices including light‐emitting diodes and photovoltaics …”