Photocontrolled Variations in the Wetting Capability of Photochromic Polymers Enhanced by Surface Nanostructuring

The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation since the embedded nonpolar spiropyran molecules convert to their polar merocyanine isomers. The process is reversed upon green laser irradiation. Structuring of the photochromic polymeric surfaces with soft lithography enhances significantly the hydrophobicity of the system, indicating that the water droplets on the patterned features interact with air that is trapped in the microcavities, thus creating superhydrophobic air−water contact areas. Furthermore, the light-induced wettability variations of the structured surfaces are enhanced by a factor of 3 compared to those on the flat surfaces. This significant enhancement is attributed to the photoinduced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the l..

Controlling the reversible wetting capability of smart photochromic-polymer surfaces by micro patterning

We demonstrate the wetting behavior control of polymer surfaces doped with photochromic molecules by modifying the surface patterning features introduced by soft molding lithography. Such surfaces enhance their hydrophilicity upon UV irradiation due to conversion of the non-polar spiropyran dopant molecules to their polar merocyanine isomers. The process is reversed upon visible light irradiation. By changing the topological parameters of the introduced pattern, one achieves surface tuning from hydrophobic to hydrophilic situations. The difference for the contact angles between UV- and green-irradiated surfaces may become significantly higher than for the flat surfaces, for the specific patterning parameters analyzed