The effect of femtosecond laser fluence and pitches between V-shaped microgrooves on the dynamics of capillary flow

Open microgroove is one kind of capillary-driven superwicking surface structure. In this study, arrays of parallel V-shaped microgrooves were fabricated on an aluminum surface by using a femtosecond laser to obtain a superwicking surface which can quickly transport the water uphill against gravity. The relationships between the flowing time and flowing distance were investigated and compared with theoretical results. We demonstrated both laser fluence and scanning step size can affect the superwicking performance. The aluminum surfaces fabricated at a laser fluence of 18.49 J/cm2 and 52.67 J/cm2 showed the best superwicking performances with the average water flow velocities approximately 16.2 mm/s and 16.4 mm/s, respectively, in the distance of 30 mm. On the other hand, the superwicking surfaces show an anisotropic flow characteristic due to the parallel microgrooves structure. However, when the scanning step size drops to 25 µm, the surface will form irregular rough structures that result in the isotropic flow characteristics. Moreover, by using a thermal camera, we found that after a 10 µL water droplet was dropped into the heated surface, the superwicking surface temperature quickly dropped from 92.4 °C to 82.5 °C which indicated that laser processing of the superwicking surface has potential application in heat dissipation.