Multiscale Hierarchical Surface Patterns by Coupling Optical Patterning and Thermal Shrinkage

A.P. and C.F. gratefully acknowledge the Finnish Cultural Foundation and the Emil Aaltonen Foundation for financial support. The work utilized the facilities of the Otanano and RAMI national research infrastructure and the cleanroom facilities of Micronova. J.V. acknowledges with gratitude funding from the Academy of Finland (Decision Number: 322214) and Flagship Programme, Photonics Research and Innovation (PREIN, Decision Number: 320167). Herein, a simple hierarchical surface patterning method is presented by effectively combining buckling instability and azopolymer-based surface relief grating inscription. In this technique, submicron patterns are achieved using azopolymers, whereas the microscale patterns are fabricated by subsequent thermal shrinkage. The wetting characterization of various topographically patterned surfaces confirms that the method permits tuning of contact angles and choosing between isotropic and anisotropic wetting. Altogether, this method allows efficient fabrication of hierarchical surfaces over several length scales in relatively large areas, overcoming some limitations of fabricating multiscale roughness in lithography and also methods of creating merely random patterns, such as black silicon processing or wet etching of metals. The demonstrated fine-tuning of the surface patterns may be useful in optimizing surface-related material properties, such as wetting and adhesion, producing substrates that are of potentialinterest in mechanobiology and tissue engineering.