Janus Fabric with Self‐Propelled Directional Wetting Patterns Induced by Light and Temperature

Janus fabric with self‐propelled directional wetting patterns is achieved. First, the fabric substrate is coated with photosensitive oxide‐based nano titanium dioxide (TiO 2 ) and subjected to post‐thermal treatment to make it superhydrophobic. Then one side of the fabric is photo‐irradiated with ultraviolet (UV) light through a photo mask to transform the irradiated surface from a superhydrophobic to a superhydrophilic one. As a result, two opposing wettabilities are formed on one side of the fabric surface whereas the opposite side retained its superhydrophobicity. The fabric system utilizes the dual stimuli‐responsive properties of nano TiO 2 : the well‐known, light‐induced superhydrophilicity; and the rarely studied, thermally induced superhydrophobicity. These two properties give rise to the self‐propelled movement of liquid in two and three dimensions: the liquid moves spontaneously from the superhydrophobic side to the opposite side and then it spreads out along the wetting patterns. The wetting pattern formed only on one side of the fabric without penetrating through to the superhydrophobic side. Such self‐propelled directional wetting patterns arise from a combination of the photo‐ and thermal‐induced chemical change of surface properties of TiO 2 as well as the wetting contrast of the macroscale and nanoscale that developed within the fabric system facilitate the directional movement of liquid.