Lotus Leaf Effect: Realization methods and their applications in textile fabrics

1.Principle of the Lotus Effect

In the 1990s, German scientists W. Barthlott and C. Neinhuis conducted research on hundreds of plant leaves represented by lotus leaves. They concluded that the self-cleaning property of lotus leaves mainly stems from two factors: (1) The epidermis of lotus leaves is coated with a layer of waxy crystals, which are insoluble lipids with hydrophobic chemical properties, endowing the leaves with excellent water-repellent characteristics; (2) The lotus leaf surface has tiny papillary structures. When water falls on the leaf surface, these papillary structures prevent direct contact between water droplets and the leaf surface, making the wetting process difficult to proceed. A surface is called a superhydrophobic surface when the contact angle between water droplets and the surface exceeds 150 degrees.

Building on this, the research team led by Academician Jiang Lei conducted more in-depth and detailed studies. They found that the micron-scale papillary structures on the lotus leaf surface are further equipped with finer nano-scale branched structures. This micro-nano composite structure effectively prevents water droplets from infiltrating the underlying structure and is the key factor contributing to the superhydrophobic and self-cleaning effect of lotus leaves.

2. Preparation Ideas of Lotus Effect Materials

Overall, the preparation methods for lotus-effect-inspired hydrophobic surfaces are divided into two categories: top-down and bottom-up.

The top-down method generally refers to fabricating nanoscale materials from macroscopic objects through techniques such as photolithography, cutting, and templating. For example, using the lotus leaf surface as a template, a layer of PDMS is coated on it. After shaping, the PDMS is peeled off to form an inverse replica complementary to the lotus leaf surface structure. Subsequently, this inverse replica is used as a new template, and the above operation is repeated to prepare a positive replica with the same structure as the lotus leaf surface. Experimental results show that this positive replica exhibits the same superhydrophobic properties as natural lotus leaves, with a surface contact angle reaching 160 degrees.

In contrast, the bottom-up method starts with atoms, molecules, or other nanoscale raw materials, and manufactures the desired nanostructures or devices through methods such as chemical deposition, self-assembly, and sol-gel. For instance, using Zn(NO₃)₂, NH₄Cl, urea, and ammonia water as starting materials, a superhydrophobic surface containing ZnO nanorods was successfully prepared on a glass substrate via chemical deposition.

3. Applications of the Lotus Effect

Textile Fabrics: Textile fabrics with the superhydrophobic and self-cleaning properties of the lotus effect have been prepared through various methods. Such fabrics must meet the following requirements: ① Breathable, allowing water vapor molecules to pass through; ② Water-repellent, where water droplets form beads on the fabric surface and roll off, carrying dust particles away; ③ The fabric surface achieves nanoscale roughness, rather than taking fibers as the smallest unit. Based on the above analysis, the ideas for constructing lotus-effect textile materials are as follows: ① Mimic the nanoscale protrusions on the lotus leaf surface to prepare fabrics with a relatively rough surface; ② Mimic the insoluble lipid film covering the lotus leaf surface and apply it to the fabric surface; ③ Coat the fabric surface with a water repellent.

Clothing with superhydrophobic and self-cleaning properties has been developed by many researchers. For example, some researchers constructed rough fabrics with superhydrophobic surfaces (taking polyester as an example) by combining silver nanoparticles and a polystyrene graft layer. Similarly, other researchers obtained lotus-effect-inspired waterproof and moisture-permeable fabrics by adding fluorine-containing water repellents to the fabric surface.