Study On Micro-nano Structures And Wettability Of Aluminum Surfaces Induced By Nanosecond Laser

Super hydrophobic surfaces is becoming a highly active area of research in recent years because its properties in industrial applications.Many existing methods for the preparation of super hydrophobic surfaces are based on two steps,the first being the generation of hierarchical micro-nano structures followed by the modification of that surface by the addition of low surface energy materials.This paper proposes a fast non-chemical method for the preparation of super hydrophobic surfaces utilizing aluminum substrates using a pulsed nanosecond laser to generate the microstructure combined with a heating process to effect the surface chemistry change.A pulse width of 240 ns was used to scan the aluminum plate surface where the spot diameter was 50?m,the scan direction overlap was69% and the vertical scanning interval was 14.75?m.Varying pulse energy allowed Aluminium processing with different laser fluencies and the subsequent surfaces were heated for 12 h in an oven to yield super-hydrophobic surfaces with a water contact angle of up to 166.1° and that displayed low hysteresis having a rolling angle of 7.2°.Through the analysis of the sample surface morphology and surface composition it is observed that,with the increase of the laser fluence,the surface roughness progresses through a sharp rise to ultimately achieve a steady state.When the laser fluence is greater than 25 J/cm~2,hierarchical micro-nano structure on the aluminum plate surface is readily observed with water being more than 90% is contact with the air as opposed to the metal surface.After baking the aluminum plate,the surfaces were found to contain measurable amounts of carbon based matter and we conclude that the aluminum plate surface wettability change is the combined result of laser generated surface morphology and chemical composition.Processing of the aluminum plate was also conducted by varying six different pulse widths whilst otherwise employing constant laser processing parameters and combining these laser processing conditions with other post-exposure factors: temperature,humidity and time.Temperature was observed to be the main factor affecting the sample surface and water contact angle revealing that different post exposure storage temperature needed different post-processing time to become hydrophobic or super-hydrophobic.Laser fluence also is also influential in the time required for the sample to exhibit non-wetting behavior.Humidity was shown to have are makeable effect on the oil contact angle as determined by measuring the oil angle of a “heavier than water” oil substitute,di-iodomethane,underwater.In summary,surfaces with different wettability can be achieved through controlling the temperature and humidity that ns laser roughened samples experience after laser processing.Optimum conditions to achieve the hydrophobic and oleophilic surfaces were found to be at a temperature of 80? and a relative humidity of 90%.This paper studies the mechanism of aluminium plate surface wettability by nanoseconds fiber lasers.In order to achieve a good super hydrophobic surface structure,the relationship between surface roughness and microstructure with surface wettability have been analyzed.The post-processing factors of temperature,humidity and time are highly influential and enable the generation of surfaces with different oil and water wettability to be obtained.