펨토초 레이저를 이용한 극친수성 금속 표면 가공

Abstract

Wettability is an important characteristic of solid surfaces, and is usually measured by the contact angle between water and the surface. Since hydrophilic surface has been used in many kind of area such as heat transfer device, there has been many researches about introducing the technique to fabricate hydrophilic surface. However, laser processing is the most useful method since it could be applied in a wide range of materials and no specific environment like clean room facility is needed for processing. Especially, femtosecond laser can fabricate micro/nano structures on metal surface much more precisely and more controllably, which is important factor for fabricating hydrophilic surface. In this work, we optimize femtosecond laser processing method for fabricating micro/nano structures on metal surfaces to make surface superhydrophilic and analyze the effect of laser-generated micro/nano structures on wetting behavior. Femtosecond laser can fabricate micro/nano periodic surface structures, which is laser induced periodic surface structure(LIPSS) and these surface topography changes with laser parameters. The size of micro/nano structure decreases, nanovally get deeper and the number of nanovelley increases and ripples agglomerate together by thermal effect. As the surface morphology changes, contact angle gradually decreases and finally, surface become superhydrophilic. Also, nanovalley can induce capillary wicking which induces liquid spreading. These phenomena are important in applications of hydrophilic surface.