ENSCHEDE, the Netherlands - Scientists at the University of Twente’s MESA+ Institute for Nanotechnology have developed a new material that is not only extremely water repellent but also extremely oil repellent. It contains minuscule pillars that retain droplets. What makes the material unique is that the droplets stay on top even when they evaporate. This opens the way to such things as smartphone screens that really cannot get dirty. The study appears as the cover story in the scientific journal Soft Matter.

Water-repellent surfaces can be used as a coating for windows, obviating the need to clean them ever again. These surfaces have an orderly arrangement of tiny pillars less than one-hundredth of a millimeter high (similar to a bed of nails but on an extremely small scale). Water droplets stay on the tips of the pillars, retaining the shape of perfectly round tiny pearls. As a result, they can roll off the surface like marbles, taking all the dirt with them.

Nanotechnologists at the University of Twente have now managed to create a silicon surface that retains not only water droplets but also oil droplets like tiny pearls. What makes the material unique is that the droplets remain in place even when they evaporate (get smaller).

With existing materials, evaporating droplets drop down between the pillars onto the surface after a while, changing in shape to hemispheres that can no longer simply roll off the surface. The surface can therefore still get dirty. By modifying the edges and the roughness of the minuscule pillars, the UT scientists have managed to create a surface on which the droplets do not drop down even when they evaporate, but stay neatly on top.

Surfaces that repel both water and oil are currently used, among other things, as a dirt-resistant coating on smartphones screens. In practice, the screens still get dirty, showing things such as greasy fingerprints. The material developed by the UT scientists brings screens that really never get dirty a lot closer.

The research was done by Arturo Susarrey-Arce, Álvaro Marín, Hrudya Nair, Leon Lefferts, Han Gardeniers, Detlef Lohse and Arie van Houselt of the Mesoscale Chemical Systems, Catalytic Processes and Materials and Physics of Fluids research groups of the University of Twente’s MESA+ research institute. The study appears in the scientific journal Soft Matter.