Reversibly Light-Switchable Wettability of Hybrid Organic/Inorganic Surfaces With Dual Micro-/Nanoscale Roughness

Here, an approach to realize smart solid substrates that can convert their wetting behavior between extreme states under selective light irradiation conditions is described. Hybrid organic/inorganic surfaces are engineered by exploiting photolithographically tailored SU-8 polymer patterns as templates for accommodating closely packed arrays of colloidal anatase TiO2 nanorods, which are able to respond to UV light by reversibly changing their surface chemistry. The TiO2-covered SU-8 substrates are characterized by a dual micro-/nanoscale roughness, arising from the overlapping of surfactant-capped inorganic nanorods onto micrometer-sized polymer pillars. Such combined architectural and chemical surface design enables the achievement of UV-driven reversible transitions from a highly hydrophobic to a highly hydrophilic condition, with excursions in water contact angle values larger than 100 degrees. The influence of the geometric and compositional parameters of the hybrid surfaces on their wettability behavior is examined and discussed within the frame of the available theoretical models.