Objectives: Omniphobic surfaces, which have both hydrophobicity and oleophobicity, are needed as an industrial application technique because liquid in the environment is a complex mixture of water and oil. The purpose of this study was to optimize the fabrication conditions on a polymer using direct laser interference patterning (DLIP) with a high liquid repellency and durability.

Methods: An optical unit was fabricated from (i) a liquid crystal on a silicon-spatial light modulator (LCOS-SLM; Hamamatsu Photonics K.K., Japan), (ii) a collimated lens (f1 = 200), (iii) a mask with two holes (200 μm of hole diameter), (iv) a beam expander (f2 = 60 and f3 = 300), and (v) an aspheric condensing lens (f4 = 20). Patterned surfaces were produced on a polyethylene terephthalate by two-beam laser interference using a femtosecond laser (Pharos-6W, Light Conversion UAB, Lithuania) at a wavelength of 515 nm, pulse length of 277 fs, repetition rate of 10 kHz, fluence of 0.04 J/cm2, and spot diameter of 220 μm. The surface free energy of the patterned surface samples was lowered after dipping the sample into a 0.5% fluoroalkylsilane (1H,1H,2H, 2H-perfluorodecyltrimethoxysilane) solution (in alcohol) for 36 h. As the final step, silicone oil was infused as the lubricating fluid, which wet and infused into the laser-induced micropores due to oleophilicity and resulted in the formation of a lubricating layer on the sample surface. Various periodic structures were compared based on repetition shots between 20 and 100 and pulse intervals between 0.5 and 8 ms using a scanning electron microscope (JEM-6010LA, JEOL Ltd., Japan).

Results and Discussion: Both the sliding speed and sliding durability increased in proportion to the depth of grooves. The amount of silicone oil supplied from the groove of the periodic structure increased in proportion to the depth of grooves; therefore, the oil film thickened. On the other hand, both the sliding speed and sliding durability decreased in inverse proportion to the surface roughness. This might be due to the smaller surface roughness and the lower contact between the surface textures and the droplets.

Conclusion: The depth of grooves and surface roughness affected the sliding speed and sliding durability. This technology might be an effective physical treatment in liquid repellency and is expected to be an approach for decarbonization.