Island Organization of TiO2 Hierarchical Nanostructures Induced by Surface Wetting and Drying

We report on the reorganization and bundling of titanium oxide nanostructured layers, induced by wetting with different solvents and subsequent drying. TiO2 layers are deposited by pulsed laser deposition and are characterized by vertically oriented, columnar-like structures resulting from assembling of nanosized particles; capillary forces acting during evaporation induce bundling of these structures and lead to a micrometer-size patterning with statistically uniform islands separated by channels. The resulting surface is characterized by a hierarchical, multiscale morphology over the nanometer-micrometer length range. The structural features of the pattern, i.e., characteristic length, island size, and channel width, are shown to depend on properties of the liquid (i.e., surface tension) and thickness and density of the TiO2 layers. The studied phenomenon permits the controlled production of multiscale hierarchically patterned surfaces of nanostructured TiO2 with large porosity and large surface area, characterized by superhydrophilic wetting behavior without need for UV irradiation.