Monolithic, Hierarchical Surface Reliefs by Holographic Photofluidization of Azopolymer Arrays: Direct Visualization of Polymeric Flows

Hierarchically ordered, monolithic surface reliefs have attracted a great deal of interest due to their applications in advanced photonics and interface sciences. While many impressive achievements in fabrication of such surface reliefs have been made over the last decade, all established methods are still restricted by a number of factors, such as limited control of structural features, inherently induced structural defects, impractically low throughput, and technical barriers caused by mechanical contact. Herein, a deterministic and scalable fabrication of hierarchically ordered, monolithic surface reliefs by holographic photofluidization of azopolymer line arrays is demonstrated. In particular, it is shown that the structural features of monolithic surface reliefs including shapes and modulation heights can be deterministically tunable by adjusting the polarization and irradiation time of the holographic interference pattern. Moreover, by a direct visualization of azopolymeric flow according to the light polarization, a long‐standing question about the origin of surface‐relief‐grating formation on azopolymer film is addressed in terms of polymeric flows. Finally, as proof of concept for the practical application of the obtained hierarchical surface reliefs, dependence of wetting properties on modulating height is demonstrated. Directional photofluidization allows a facile fabrication of various large‐area, hierarchically ordered monolithic surface‐relief gratings (SRGs) with precisely controlled structural features. Furthermore, the use of a micrometer‐scale periodic line pattern rather than a flat thin film, which has been generally used in conventional SRG studies, provides a powerful way to quantify the direction of flows of azopolymer during SRG formation.