Mechanism Of Hydrophobicity Transition On Silicone Rubber Surface Induced By Femtosecond Laser

Silicone rubber insulator has been widely used on the power transmission lines at home and abroad due to its good hydrophobicity and mechanical strength.In order to further improve the surface hydrophobicity of the silicone rubber insulating material,femtosecond laser was used to modify its surface.According to the change characteristics of wettability of silicone rubber by femtosecond processing,the relationship between the surface physical property and wettability was emphatically discussed.On this basis,the influence mechanism of laser processing parameters on various physical and chemical changes on the silicone rubber surface was discussed.Combined with the specific use environment of silicone rubber insulating material,the influence of actual environment on the subsequent change of wettability was analyzed.The research results shows that after etching by femtosecond laser,the surface wettability of the silicone rubber surface has a obvious transition process of loss and recovery:After femtosecond laser treatment,the hydrophobicity of the silicone rubber surface decreased obviously,and the contact angle dropped from about 110°to a minimum of about 35°.This loss of hydrophobicity was mainly caused by the increase of the hydrophilic-OH groups and the decrease of the hydrophobic-CH₃ groups on the sample surface.However,after the femtosecond etched samples were stored in the natural environment,it was found that the surface hydrophobicity gradually recovered and further developed into a superhydrophobic state.The water contact Angle of the surface could rise to more than 160°,and the rolling Angle could drop to less than 5°.It was found that the microstructure and chemical groups on the surface of the samples did not change significantly during storage,and that the migration of LMW cyclic and/or linear siloxane oligomers was responsible for the recovery of hydrophobicity.In addition,the surface roughness is a prerequisite for converting the wettability of the silicone rubber insulator surfaces into a superhydrophobic state.When the sample surface was irradiated with a small laser fluence,a larger roughness appears on the surface.Since the chemical change produced at this time is not obvious,the laser-treated silicone rubber surface immediately shows a good hydrophobicity after processing,and there was no obvious change with the increase of storage time.As the laser fluence increases,the influence of the changes in the chemical groups of the silicone rubber surface on its wettability dominates.So the hydrophobicity of the sample surface shows the obvious loss and recovery characteristics.On this basis,this work further explores the subsequent changes in the surface wettability of silicone rubber in the actual use environment.By simulating the sun and rain conditions in the natural environment,a 700-hour accelerated aging test was carried out on the silicone rubber processed by the femtosecond laser.The results show that the contact angle of the sample surface will drop to 150°after accelerated aging.Among them,the sample treated with a laser fluence of 5J cm^-2 has the best hydrophobicity after aging.It was found that the sun and rainfall had a significant impact on the microstructure of the silicone rubber surface,and induced the generation of hydrophilic-OH groups and carbonyl groups.The hydrophobicity of silicone rubber surface will decrease due to the changes of surface microstructure and chemical groups.By exploring various physical and chemical changes of silicone rubber surface by femtosecond laser processing,the relationship between surface physical properties and wettability evolution process was established.The research results have a good theoretical guiding value for understanding the mechanism of silicone rubber surface wettability,thereby constructing an effective silicone rubber hydrophobic surface,and improving its reliability in the practical application environment.