Ultra-hydrophobic materials

The Lotus Effect

A special family of nano-powders was developed, capable of forming surfaces with exceptional super-hydrophobic (or ultra-hydrophobic) properties. This effect is characterized by the formation of spherical droplets of water on the surface, without any wettabillity.

In nature, such properties are characterized by the "lotus effect". Lotus leaves exhibit very high water repellency, which is caused by the combination of a complex nano-scopic surface structure and hydrophobic micro-surface properties of the leaves. Water repellency results in high mobility of water droplets on the leaves. It gives the leaves unique sefl-cleaning properties, as the droplets pick up dirt particles while rolling away.

The shape of the water droplets and either hydrophobic or hydrophilic properties of a surface are determined by the "contact angle". The higher the contact angle the higher the hydrophobicity of a surface, resulting in a very limited contact area between the droplet and the surface i.e. more spherical shape of the droplets. Surfaces with a contact angle < 90° are referred to as hydrophilic and those with an angle >90° as hydrophobic.

Contact angles of 160° and above are called super-hydrophobic meaning that only several % of a droplet base is in contact with the surface. This gives an almost spherical shape of the water droplet and as a result - increased ability to to move (roll) on the surface. The ultra-hydrophobic effect is shown on the pictures showing spherical water droplets on the surface formed of the nano- powders developed by Hydrogen Link.

Superhydrophobic materials lead to significant practical industrial applications, such as self-cleaning surfaces and water repelling coatings.