Designing Bionic Micro-Nanostructures For Creating A Superhydrophobic Coating With Icephobicity And Corrosion Resistance

Since an artificially superhydrophobic surface inspired by the water-repellent of lotus leaves was reported,researchers have tried various methods to develop different kinds of superhydrophobic coatings on the basis of a unique functionality of the flora and fauna in nature.It is generally believed that superhydrophobic coatings have versatile applications such as self-cleaning,anti-icing,corrosion resistance and oil-water separation.The freezing of water droplets under low temperature conditions is a common phenomenon in nature,but this kind of ice grows and accumulates on the material surfaces brings a lot of trouble to human life.Likewise,material corrosion has been a major problem threatening the development of the world’s industry because the corrosion of materials is an irreversible phenomenon in nature.Superhydrophobic coating is favored by many researchers due to its strong water-repellent characteristics,and thus such a coating provides innovative ideas for the applications of anti-icing and anti-corrosion on the material surfaces.Regarding to current superhydrophobic coatings,poor mechanical stability and insufficient chemical durability have always been a problem to be solved.Moreover,many problems such as sophisticated and time-consuming operations,expensive raw materials,toxic chemicals and environmental pollution hinder the real-time applications of the superhydrophobic coatings.With the development of the superhydrophobic coatings,the challenges,research controversies and academic blind areas in the field of superhydrophobicity become increasingly obvious.The existence conditions and mechanism of the anti-icing properties need to be explained for the superhydrophobic coatings.The relationship between the bionic micro-nanostructures,low surface energy,the icing nucleation theory of small droplets,the energy conversion of the icing interface and the ice adhesion strength on the iced surface needs to be further analyzed.On the other hand,the corrosion resistance of the superhydrophobic coatings needs to be improved.The anti-corrosion mechanism of the superhydrophobic coatings based on the model of air pockets still needs to be explained deeply.More importantly,a superhydrophobic coating with single function can no longer meet the requirements of the development of the times for materials.Therefore,creating a superhydrophobic coating with anti-icing and anti-corrosion properties will be an inevitable trend in future researches.A time-saving method based on chemical etching and fluorine-free STA modification is employed to create a superhydrophobic coating on different kinds of metals such as aluminium alloy.There are irregular rough structures on the resultant superhydrophobic coatings.In this section,the influence of a synergistic etching treatment by hydrochloric acid and hydrogen peroxide on the irregular rough structures and the surface wettability after stearic acid modification is analyzed.The relationship between the surface rough structures and the water sliding angle on the superhydrophobic coating is revealed.It should be noted that this superhydrophobic coating can show the bouncing dynamics for different sizes of a water droplet.On the basis of the analysis results of bouncing dynamics,our group believes the water sliding angle of below 1°is the vital for a superhydrophobic coating achieving excellent properties such as the self-cleaning and surface anti-icing.In addition,the self-cleaning,anti-icing and anti-corrosion properties of the resultant superhydrophobic coating are measured and analyzed.A laser texturing technique can endow bare aluminum alloy surface with regular dimple-pattern array and thus generates a case hardening.After the fluorine-free STA treatment,these laser-textured samples become superhydrophobic.The surface wettability of the laser-textured samples can be regulated by controlling the dimple-pattern dimensions during the laser processing.In this section,the influence of a synergic relationship of multiple factors such as laser texturing geometry,array distribution and chemical composition on the surface superhydrophobicity and low water adhesion is revealed.The principle of tribology is employed to analyze and demonstrate that the laser-textured superhydrophobic surface has excellent mechanical stability.It is noteworthy that a fluorescence method is utilized to record the zones on the superhydrophobic surface penetrated by small enough water droplets.Compared with a general method of the Cassie-Baxter theoretical calculation,this fluorescence method intuitively exhibits the air trapping ability of the superhydrophobic surface.The reason that superhydrophobic surfaces with the same water contact angle show different water sliding angles is explained.In addition,an ice adhesion strength device at low temperature is built.The testing results show that small size of micro-nanoscale structures is beneficial to obtain an ultralow water sliding angle on the metals for achieving anti-icing performance,but it is not conducive to the ice removal when its surface iced.The two-dimensional（STA-PDMS sample）and three-dimensional（STA-PDMS-Zn O sample）superhydrophobic coatings are prepared by the same fluorine-free STA modification method.The difference between two kinds of superhydrophobic coatings in the preparation is whether adding raw Zn O powders to the STA-PDMS modifier.By the comparison of two superhydrophobic coatings on the corrosion resistance,the research results demonstrate that the construction of a three-dimensional surface structure is beneficial to improve the corrosion resistance of the superhydrophobic coating.Based on the results of the corrosion resistance comparison,it is illustrated that not all superhydrophobic coatings can provide corrosion protection to the substrate.A superhydrophobic STA-PDMS-Zn O coating with stepwise multilayered micro-nanostructures is designed and prepared to extend the engineering service life of the superhydrophobic surface.The resultant superhydrophobic coating shows excellent repellency to water with a water contact angle of 152°and a water sliding angle of below 2°.A synergistic method of fluorine-free superhydrophobic nanoparticles and epoxy resin curing is employed to develop a nano-functionalized superhydrophobic coating.A relatively smooth surface structure in the microscale but rough in the nanoscale is detected within this nano-functionalized superhydrophobic coating.The free-sliding phenomenon of one water droplet between two superhydrophobic coatings,the water rebounding and bouncing phenomenon on the superhydrophobic coating indicate that the non-fluorinated and nano-functionalized superhydrophobic coating has excellent repellency to water.Besides,this superhydrophobic coating has strong mechanical stability and good chemical durability against acid/alkaline droplets even though upon being scratched or left traces.More importantly,such a coating has the integrated characteristics of anti-icing and anti-corrosion.In this section,a Programmable Temperature&Humidity Chamber is modified to measure the anti-icing performance of the nano-functionalized superhydrophobic coating.The testing results show that the resultant superhydrophobic coating has a strong effect of delaying icing on its surface.When this superhydrophobic coating surface is frozen,the ice adhesion strength between the coating and the ice is 53.6 k Pa,thus the ice on the surface of the nano-functionalized superhydrophobic coating is easy to remove.Simultaneously,the anti-icing mechanism of the nano-functionalized superhydrophobic coating is explained through the classification nucleation theory of water droplets,the inhibition of nucleation energy and the thermodynamic relationship between the three-phase interfaces.In addition,the corrosion current density of the resultant superhydrophobic coating in the corrosive medium is 3.744×10^-10 A·cm^-2,and its resistance value can reach the level of 8×10⁸Ω·cm².The corrosion inhibition efficiency of this coating is greater than 99.5%even after the Na Cl immersion for 5 days.And the as-prepared coating can display excellent repellency to water even through lasting immersion for 5 days.