Controlling The Surface Wettability Of Typical Materials By Nanosecond Laser And Its Application

Wettability is one of the important properties of solid surfaces.Through the study of animals and plants in nature,various solid materials with special wetting properties are applied to many fields,like self-cleaning,anti-fog,anti-icing,anti-frost,anti-corrosion and anti-pollution,underwater drag reduction,oil and water separation and other fields.The interaction between laser and matter can induce rich shape/property changes in materials,along with the laser processing process is highly controlled,it is widely used in the construction of function surface,which the surface wettability regulation is one of them.Although laser surface treatment has been widely used to control the wettability of material surface,there are still a lot of mechanisms,laws and key technical problems unsolved,which leads to the fact that the surface wettability of laser-controlled material has not been truly applied in engineering.This paper takes 304 stainless steel and carbon fiber reinforced plastic(CFRP)these two important engineering materials as target,the surface wettability was regulated by nanosecond laser,and the relevant mechanism and law were explored to provide scientific basis for the engineering application of related technologies.The specific research content and results are as follows:On the surface of 304 stainless steel,a nano-scale rough structure was constructed using nanosecond laser,after laser processing,the wettability of the stainless steel surface was quickly converted from a super-hydrophilic state to a super-hydrophobic state through a low-temperature heat treatment method.Different wettability surfaces can construct by combing laser processing and low temperature heat treatment methods,and different wettability surfaces are combined on the same surface can build a gradient wettability surface.The surface microstructu re,chemical composition,and contact angle are observed and characterized via scanning electron microscope(SEM),energy spectrum analyzer(EDS),and contact angle measuring instrument.A high-speed CCD camera is used to observe the motion of droplet on the gradient wettability surface.The experimental results show that the content of the carbon(C)on the surface is an important factor that affects surface hydrophobicity after laser processing.For 304 stainless steel,short-time heating at temperature of 200? accelerates the increase of the C content,realizing fast curing of contact angle.Reasonable design of material surface with contact angle gradient can realize directional movement of the droplet on its surface.By further controlling the distribution of the contact angle gradient on the surface of the material,it is possible to control the moving speed and moving distance of the droplet on the surface.The research results can be used in engineering fields such as microfluidics and underwater drag reduction.The surface wettability of CFRP material is controlled by nanosecond laser.CFRP is processed with different laser parameters and then the processed samples are abhesived to test the adhesive strength to evaluate the influence of surface wettability and surface roughness on adhesive strength,The surface microstructure,contact angle and surface roughness are observed and characterized via scanning electron microscope(SEM),contact anglemeasuring instrument and optical profiler.A u niversal electronic experimental machine is u sed to observe the tensile and shear strength,and make a comparative analysis with unprocessed sample and mechanical processed(sanding)sample.The experimental results show that with different laser parameters,the epoxy resin adhesive on the surface of CFRP can be removed to control its surface wettability and surface roughness,and then change its adhesive strength.Compared with unprocessed CFRP samples,after laser surface processing,the wettability of CFRP sample surface is improved,the surface roughness is increased,and the bonding strength is also increased.Compared with mechanical processed CFRP samples,the surface wettability and surface roughness of laser-processed CFRP samples are greater than mechanical processed CFRP samples.However,the heat-affected region caused by nanosecond laser treatment of CFRP has a weakening effect on the strength near the adhesive region,therefore,the adhesive strength of the nanosecond laser treated samples is lower than mechanical processed samples.The above results show that the surface wettability and surface roughness of carbon fiber material have a significant influence on the adhesive strengh,in the way that the stronger the hydrophilicity is and the greater the roughness is,the greater the adhesive strength is.Choosing appropriate laser processing parameters can effectively regulate the adhesive strength of CFRP.The results provide a reliable experimental basis for CFRP adhesive technology.