Biomimetic, hierarchical structures on polymer surfaces by sequential imprinting

Thermal nanoimprint lithography (NIL) is based on the thermo-mechanical deformation of a polymer film above the glass transition temperature (Tg) and at an applied pressure. Sequential imprinting extends the process of thermal NIL to create hierarchical structures by carrying out secondary and tertiary imprintings at temperatures below the Tg of a polymer. In this work, we demonstrate the use of sequential imprinting technique to fabricate two- and three-level hierarchical structures on polystyrene (PS) and poly(methyl methacrylate) (PMMA) films over a temperature range of 70-130 °C, with the aim to mimic the hierarchical structures found in biological systems. By mimicking the hierarchical structure in a plant leaf, the water contact angle of PS film was increased from 95° to 128°, while the water contact angle of PMMA film was increased from 71° to 104°, without any chemical treatment.