Development of Super-Water Repellent Material from Fullerenes

A team headed by Senior Researcher Takashi Nakanishi of the Organic Nanomaterials Center of the National Institute for Materials Science (President: Prof. Teruo Kishi), and also of the member of the Max-Planck Institute of Colloids and Interfaces, Potsdam, Germany, fabricated micro-sized particles with a nano-sized flake structure on the surface using fullerenes, which are a type of carbon-based nanomaterial, and discovered that a thin film of this structure spread on a substrate expresses a super-water repellent function, repelling water in a manner similar to a lotus leaf.
Fullerenes are a nano-type carbon material which is expected to be used in a variety of applications, including electronic materials, medical materials, hard additives, and others. However, because the current applications as an actual applied material include only an extremely limited number of examples, such as hard polymers additives and additives for lubricants, there is a strong desire for the development of new material applications. On the other hand, the self cleaning function displayed by lotus leaves in the natural world is based on the super-water repellent (SWR) property, by which the leaf surface repels water. Many research projects are investigating the creation of artificial SWR films which imitate this function using fluorine based polymers, etc. However, to date, there had been no examples of application of fullerenes as an SWR material, even though it is known that fullerenes, like fluorine based materials, have small surface free energy.
Dr. Nakanishi's team succeeded in creating a spherical micro-particle (micrometer-sized diameter) with a nanometer-sized flake structure on its surface by self-assembly, in a solvent, of a fullerene compound in which 3 alkyl chains were introduced as substituents. When these particles are coated on a substrate and a thin film is formed, it was found that a surface with a fractal shape is formed, and the film displays a super-water repellent property, having a 152° contact angle of water with this surface. The fractal shape and SWR property of this SWR film were unchanged after exposure for more than 36 hours at 100°C, and the film also displayed extremely high durability with respect to polar organic solvents (acetone, ethanol), and acid and basic solutions. This technology can be considered extremely significant, not only because it is the first method of creating an SWR film using a fullerene material, but also because it imitates the surface system of the lotus leaf in the natural world with only self-assembly and hierarchization of organic molecules.
The technology for creating an SWR film using fullerenes as the basic material in this invention has a number of advantages, including the simplicity of the technique itself, the fact that selection of the substrate is not necessary, and excellent resistance to a variety of environments, and is therefore useful both as a new SWR material and as a novel application of fullerenes. Because this fullerene compound dissolves readily in nonpolar organic solvents (toluene or chloroform) and can be recovered and reused, cost reduction is expected. Moreover, because this is a material which is based on organization of molecules, it also has considerable unexplored potential as a soft material.
The results of this research are scheduled to be published in the near future in the international scientific journal "Advanced Materials."