Femtosecond laser manipulating underoil surface wettability for water removal from oil

The oil containing a small amount of water droplets have induced serious operation malfunctions for precision industrial equipment and even brought fatal disasters, which have aroused widespread concern. However, developing an effective strategy for removal of water from oil is still an enormous challenge. Here, we present a rapid and facile method for fabricating underoil superhydrophilic surface by one-step femtosecond laser direct writing technology. Interestingly, two extreme underoil wettability statuses can be achieved through tuning the scanning velocity (V). Concretely, the pristine underoil hydrophobic titanium sheet will become underoil superhydrophilicity when V is 0.1 m/s, while it will exhibit underoil superhydrophobicity when V increases to 3 m/s. Moreover, the underoil superhydrophilic surface shows excellent water absorption, which could realize the purification of oil contains water droplets regardless of the oil types, and the corresponding mechanism is propounded. We believe that femtosecond laser micromachining has tremendous superiority in solving the problem of oil containing water droplets.