Laser textured superhydrophobic surfaces and their applications for homogeneous spot deposition

- Hierarchical structures textured on stainless steel using nanosecond fiber laser.
- Wettability changes from hydrophilicity to superhydrophobicity after 13 days.
- Contact angle of 154° and contact angle hysteresis of 4° are obtained.
- Uniform film deposition observed rather than coffee-ring stain.
- Deposited area is one order of magnitude smaller than the coffee-stain.

This work reports the laser surface modification of 304S15 stainless steel to develop superhydrophobic properties and the subsequent application for homogeneous spot deposition. Superhydrophobic surfaces, with steady contact angle of ∼154° and contact angle hysteresis of ∼4°, are fabricated by direct laser texturing. In comparison with common pico-/femto-second lasers employed for this patterning, the nanosecond fiber laser used in this work is more cost-effective, compact and allows higher processing rates. The effect of laser power and scan line separation on surface wettability of textured surfaces are investigated and optimized fabrication parameters are given. Fluid flows and transportations of polystyrene (PS) nanoparticles suspension droplets on the processed surfaces and unprocessed wetting substrates are investigated. After evaporation is complete, the coffee-stain effect is observed on the untextured substrates but not on the superhydrophobic surfaces. Uniform deposition of PS particles on the laser textured surfaces is achieved and the deposited material is confined to smaller area.

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