Phenomena And Mechanism Of Surface Hydrophobization

Superhydrophobic surface has wide application prospects in the fields of self-cleaning,corrosion protection and drag reduction,etc.The formation of a superhydrophoic surface requires a unique combination of low surface energy and surface roughness.In this paper,we studied some phenomenons and science issues about the methods,which can decrease the surface energy,of organic molecules self-assemnled monolayers?SAMs?and carbon deposition with the decomposition of CO₂.In addition,we also studied the forming mechanism of a novel structure on the surface of the polymer and metallic composite hydrophobic coating.The details as follows:Stearic acid?SA?SAMs were fabricated by solution deposition on single-crystal C-plane?0001?aluminum oxide?sapphire?.By annealing the SA SAMs at various temperatures,thermal stability was investigated.The results revealed that the surface coverage remains unchanged in air until the temperature reached⁸0°C,then decreases with further increasing the temperature and finally becomes zero at 220°C.Various of specific transition?phase,surface coverage rate and height difference?were found in the temperature range between 130^oC and 140^oC.The complex bonding type is thought to play an important role in the thermal desorption.It was also found that heat-treating has a great effect on the topographies of SA SAMs after washed with flow water,and the treatment of high relative humidity?RH?atmosphere can enhance the ability of SAMs to resist ethanol washing.The growth mechanism of an octadecyltrichlorosilane?OTS?self-assembled monolayer on a silicon oxide surface at various RHs has been investigated.Atomic force microscopy images show that excess water may actually hinder the nucleation and growth of OTS islands.A moderate amount of water is favorable for the nucleation and growth of OTS islands in the initial stage;however,the completion of the monolayer is very slow in the final stage.The growth of OTS islands on a low-water-content surface maintains a relatively constant speed and requires the least amount of time.The mobility of water molecules is thought to play an important role in the OTS monolayers,and a low-mobility water layer provides a steady condition for OTS monolayer growth.Meanwhile,the nano-mechanical properties of different OTS phases have also been investigated by AFM,results showed that the fine packed OTS islands have greater mechanical strength.Fluff-like structural aggregation on the surface of Cr and PFA mixture coating was produced with an improved plasma nozzle.Test results suggested that the fluff-like materials mainly stem from PFA,and the PFA in the mixture coating is essentially identical to the original PFA powders.The PFA particles were broken up by the volatiles surrounded the Cr particles in the sprayed process is thought to play an important role in forming this fluff-like structure.However,the Fe particles would not evaporate during spraying,so there is no fluff-like structure appeared on the surface of Fe and PFA mixture coating.Absorption and decomposition of CO₂ by active ferrites prepared using APS has been studied.It is found that active ferrites fabricated by APS to incorporate FeO and anoxic iron oxide[Fe₃O_4-??0<?<1?].The complexity of phase composition,especially the presence of FeO,gives the resulting powder a greater ability to decompose CO₂when compared to hydrogen-reduced Fe₃O₄ or Fe₂O₃ particles.Spraying distance is found to play an important role in modulating the decomposition ability of the powders,while elevated temperatures can also enhance the catalytic decomposition of CO₂.