State-of-the art microfabrication techniques enable new understanding of surface phenomena such as liquid wetting and dry adhesion. This understanding led to a surge of design and fabrication of novel non- and directional wetting, self-cleaning, anti-biofouling and energy efficient surface textures. This work focuses on designing new dynamic surfaces that can change their micro and nanoscale texture due to in-plane mechanical strain. The studied textured surfaces have vertical 1D nanostructures, such as carbon nanotubes, integrated on flexible carrier films with inclined angle-tunable microstructures. An example of hierarchical geometry is proposed and fabricated using a double-molding technique. Finite Element Analysis shows that the nanostructure angle can be tuned from –45 to +40 degrees while the space among their periodicity changes by 320% due to in-plane tensile film strain. Two types of molds are designed and fabricated: inclined wavy surface features fabricated with stereolithography with periodicity of 250 microns and kinematically coupled alignment grooves; tilted SU8 microstructures with periodicity of 50 microns made by inclined photolithography. Both molds were used to cast films of 100 micron thickness from polydimethyl siloxane (PDMS); and releasing the film was achieved using a sacrificial mold coating of 300 nm thick PMMA. With PDMS thin films bearing arrays of nanostructures with tunable angles, these surfaces can change surface roughness by external stimuli; for instance, by applied mechanical strain, further change a wide range of optical, wetting, adhesive and other surface properties. In other words, the strategy here is not only with reversible surface properties but also can be triggered by a wide range of stimuli.
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Design and manufacturing of PDMS micro structures with dynamic inclination angle
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