Visualization. 2. Schematic device configurations and fabrication processes

Polished titanium plates (99.99 wt.%, Sigma-Aldrich) with size of 10×10×1mm³ were used as the substrate. The equipment used in this study includes a 515 nm picosecond (ps) laser (TRUMPF, micro 5000) with 10 ps pulse width, 50 W average laser power at 400 kHz pulse repetition frequency, and less than 2% average power and pulse-to-pulse energy fluctuations. A beam expander was used to improve the laser beam quality. A 2-D galvanometer scanner system was used to control the laser beam. The focal plane was fixed on the sample surface, and the optical spot size of the focused laser beam was approximately 20 μm in diameter. The laser fluence adopted in this paper was 1.43 J/cm². After laser ablation was finished, for achieving the LASH surface, the samples were modified with 0.01 mol/L solution of stearic acid (Sigma-Aldrich) at ambient temperature for 60 min and dried in atmosphere condition. Then, the chemical modification layer was removed by the ps laser to fabricate a superhydrophilic surface with designed pattern.

The surface morphology of LASH surfaces and deposited patterns was detected using a scanning electron microscope (SEM, Zeiss, supra 55) and a laser scanning confocal microscopy (OLYMPUS, OSL 4100). The CAs and SAs were measured for five times at different tested area with 4μL water by video optic CA instrument (Dataphysics, OCA15EC). The SA was estimated as the tilted LASH surface on which deposited drops start to roll downwards. The temperature and relative humidity in this experiment were 25 ℃ and 50%.