Investigation on femtosecond laser irradiation energy in inducing hydrophobic polymer surfaces

► Ultrashort femtosecond laser pulses can induce hydrophobic properties on PMMA surfaces. ► The wettability modification depends on the laser energy deposition. ► A simple equation deduced from the laser parameters can express the energy deposition. ► Water contact angle exceeds 120° with a maximum of around 125° at the energy deposition range 600–900 J/cm 2. This study investigates the use of ultrashort femtosecond laser pulses to induce hydrophobic properties on PMMA surfaces. The modification of surface wetting property exhibits a strong dependence on the amount of energy deposited on the PMMA surface. A simple equation has been deduced from the laser parameters to express the energy deposition. It was revealed that water contact angle (WCA) of more than 120°, with a maximum of around 125°, could be achieved when the total energy deposited per unit area on the PMMA surface ranged from 600 J/cm 2 to 900 J/cm 2 at an energy deposition rate of around 50 J/cm 2/s. Beyond this range, WCA reduced with increasing amount of energy deposition. Furthermore, with higher energy deposition rate or higher laser fluence, total energy required to induce hydrophobic surfaces was reduced. Under different energy deposition, the quantity of polar groups or non-polar groups induced was responsible for the changes in WCA and thus the different surface hydrophobicity.