In oriental cultures the lotus has long been extolled as the "beauty of purity" as evidenced by the lotus eulogies of Chinese poets in ancient times. The lotus has self-cleaning function so called lotus effect which is attributed to the water- and soil-repellent characteristics of its micro- and nanostructured surfaces. To make the self-cleaning lotus effect technologically useful the lotus-like polymer surface is recently studied by J. Xu and J. Dong's groups.

The bionic polymer surface is prepared by the formation of multi-molecular micelles of polypropylene and polymethylmethacrylate copolymer(PP-b-PMMA) in N N'-dimethylformamide selective solvent. Every micelle composes of the insoluble core of PP chains and the soluble shell part of PMMA its diameter of about 50~200nm and the aggregate sphere composed by several multi-molecular micelles is mostly around 1.5~2mm. The study demonstrated that the PP-b-PMMA multi-molecular micelle aggregates provide the micro-scale roughness while the nano-scale individual multi-molecular micelles on the aggregates surface provide the nano-scale roughness. The combination of micro-scale and nano-scale roughness induces more fraction of space for the air that is trapped between the water drops and the surface. In the same time such a micro-nano-binary structure(MNBs) minimizes the contact area of polymer surface with the water drops. The contact angle and sliding angle of water drops of 5ml on the rough surface of PP-b-PMMA copolymer becomes 160.5+/-2.1o and 9+/-2.1o respectively. Obviously such a method in this study can easily be extended to prepare superhydrophobic surfaces using different types of di-block or tri-block copolymers which are the most common form in polymer materials. (Adv. Mater. 2004 16(20) 1830-1833)

 

SEM images of bionicsurface and natural lotus. (A)Surface microstructure of natural lotus leaf. (B)Micelle aggregates deposited surface cast from DMF solution at PP-b-PMMA concentration of 5*10‑2 g/ml. (C)Enlarged view of an individual sphere with MNB structure in (B).