Spraying PMMA/SiO₂ Superhydrophobic Coating On The Metal Surface And Its Properties Research

Superhydrophobic surfaces that inspired by lotus leaf have developed rapidly in recent years.Surfaces with water contact angle(CA)above 150° and sliding angle(SA)less than 10°have satisfactory applications for anti-corrosion,anti-icing,self-cleaning,drag reduction,oil purification,and medical science,etc.Multiple methods have been developed to create air-trapping and low energy surfaces,such as,chemical etching,sol-gel,chemical vapor deposition,electrodeposition,laser irradiation.However,most of those technologies need complicated processings or multistep procedures.Here,Superhydrophobic coating was fabricated by spraying the mixture of poly(methyl methacrylate)(PMMA)and hydrophobic silica nanoparticles(SNs)on steel surface.Compared with other technologies,spraying coating method is economic,simple,and convenient for substrates with different shapes.In this work,the SNs were prepared by stober process,and the prepared SNs were modified by low surface free energy components.The prepared SNs were uniform dispersion.With the addition of ammonia hydroxide(NH4OH)increasing,the particle size of SNs was larger,however,the contact angle of SNs was decrease.SNs stack in size of nanometers to several micrometers,obtaining a great deal of micropapillae and concave.With the addition of SNs increases,a great deal of micropapillaes and concaves were obtained.The research showed that the contact angle is proportional related to the surface roughness and low surface free energy.Freezing water was dropped on the superhydrophobic surface.But no ice film could be observed compared with steel substrate,due to the bouncing behavior of water droplet.In the condensing condition,the superior anti-icing behavior could be attributed to the overcooled water that formed on superhydrophobic coating.Thus,solidification process of condensed water was delayed on superhydrophobic surface.Liquid of different pH was dropped on the surface of coating,and their contact angles were measured.The coating exhibited great superhydrophobicity.An electrochemical corrosion test was carried out to investigate the corrosion resistance.Because of parallel hydrophobic plates will trap air bubbles and create volume regions where water is vanished,the superhydrophobic coating has much better corrosion resistance than the bare steel.And the superior anti-corrosion of superhydrophobic coating is not determined by the barrier effect of PMMA layer.In the drag reduce test,the drag reduce effect was dependent on Reynolds numbers and the superhydrophobicity.This dependence was examined by the rotating disc-drag tester.The superhydrophobic coating was conspicuous at low Reynolds number.But,as the Reynolds number was increased,the drag reduction rate decreased.Better superhydrophobicity ability would enhance the efficiency drag reduce.The superhydrophobic coating introduces a performance penalty in the form of a local increase in drag at the no-slip-free-slip edge.This adverse effect is caused by the inhomogeneity of the near-wall flow field.