Light-induced wettability changes on polymer surfaces

Altering the surface wettability by external stimulation has received great attention recently. While different stimuli, such as temperature, pH, etc. can be applied for this purpose, light combines several advantages. It is a contact-free stimulation, which can be applied locally, thereby allowing a versatile patterning. This review article summarizes recent developments in the area of polymers that allow a light-induced change in surface wettability. For this purpose, different photochromic dyes have been incorporated into polymers, which enable a photo-isomerization upon light irradiation resulting in a change in polarity. Several examples based on azobenzene or spiropyran will be discussed, but also some more exotic examples, such as those based on salicylideneaniline, will be highlighted. The different approaches how to apply these photochromic dyes to various surfaces are presented and discussed. Additionally, the combination with other stimuli-responsive moieties will be explored and the paper will be concluded by mentioning the remaining challenges and by providing a future perspective.