Research On The Wettability Of Micro/Nano Structured Solid Surface Fabricated By Femtosecond Laser

Various micro/nano structures can be prepared directly on the metal surface by using femtosecond laser.These structures provide the metal surface with good wettability,for example,hydrophilic or hydrophobic function.Based on these functional characteristics,they find important application in the fields such as aerospace,architecture,medicine and solar energy.In this thesis,we study the preparation of hydrophilic or hydrophobic micro/nano structured surface by femtosecond laser.In the study of hydrophilicity,the groove-like micro/nano structure was fabricated on the metal surface by focusing femtosecond laser pulse.It was found that the size of the groove structure achieved in the condition of in-focus is smaller than that in the laser defocusing condition(the groove width under in-focus condition is about 120 ?m,and the width of the micro groove at the out-of-focus condition is about 70 ?m).The finding is important for the preparation and optimization of the groove micro/nano structure.The spectral monitoring results show that this phenomenon is attributed to the non-linear phenomenon of plasma filament generated during the process of femtosecond laser focusing.On the other hand,the characterization of the hydrophilicity shows that the surface contact angle of the prepared groove micro/nano structures is about 11°,and the surface exhibits super-hydrophilic property.In the meantime,the water inhaled by micro/nano structured surface flows along the groove against gravity and the average speed can reach up to 21.6 mm/s.The inverse gravity transport of water conforms to the diffusion law,and this phenomenon is attributed to the open cavity capillary effect.In the study of hydrophobicity,we focused the femtosecond laser pulse on the nickel surface and scan with a pitch smaller than the size of focused beam size.After a homogeneous laser irradiation on the surface,a cylindrical two-scale micro/nano composite structure was prepared.We found that the wettability of micro-nanostructure surface does not spontaneously change from hydrophilicity to hydrophobicity in air,which is different from the result of micro/nano structured surface prepared on steel,titanium alloy and pure copper surface by femtosecond laser.Nevertheless the contact angle of micro/nano structured surface can reach up to 148.28 ° after silanization.This discovery is of significant importance for the selection of the base materials for the preparation of metal wettability surface by micro/nanostrctures.