Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 13: Solid / liquid interfaces I

O 13.7: Talk

Monday, March 14, 2011, 16:30–16:45, WIL B321

Light induced switching of surfaces: turning superhydrophobic into hydrophilic surfaces — •Jonas Groten and Jürgen Rühe — University of Freiburg - IMTEK, D-79110 Freiburg, Germany

We report on a method to generate a surface whose wettability can be switched between a superhydrophobic and hydrophilic state by simple, short UV irradiation. The system is based on a silicon surface with a nanoscale roughness (black silicon) to which a polymer monolayer is attached.The polymer contains a fluorinated azobenzene moiety. In these polymers the azobenzene moiety can be switched between the cis and trans states depending on the wavelength of the light used during illumination. In the described system the surface energy of the polymer coating is carefully adjusted to the energy value which separates distinct wetting regimes of the nanorough surface. This coupling of light induced switching to a wetting transition can cause large changes in the surface wetting behavior even when the surface energy is changed only in a rather small range. In one state the surface is superhydrophobic and has a critical tilt angle for roll off of only 3. Upon short illumination, however, the drop completely sticks to the surface and does not roll off upon tilting at any angle. Such strong changes in the wetting behavior offer an interesting potential for applications in microfluidic systems.