Preparation Of Superhydrophobic MnO₂Films By A Simple Hydrothermal Method And Anti-icing Behavior Study

Due to the excellent hydrophobic performance, superhydrophobic surface hasvery broad application prospects in the fields of industry, agriculture, business, andnational defense. In recent years, the research on superhydrophobic surface hasreceived much attention. Meanwhile, manganese dioxide has attracted a great deal ofattention owing to its special optical, electrical, catalytic and microwave absorbingproperties. Demands of functional applications have been driven the research ofsuperhydrophobic to move forward and keep going. Under this trend, combining theproperties listed above with superhydrophobicity could open up new possibilities forthe use of MnO2in various fields. However, up to date, the simple fabrication of asuperhydrophobic MnO2hierarchical structure has been barely reported in theliterature. Here we present simple and inexpensive ways to achieve superhydrophobicMnO2films through hydrothermal procedures in this paper. The main researchcontents and conclusions of this paper are as follows:(1) With ammonium persulfate and manganese sulfate as reactants, we preparedmanganese dioxide superhydrophobic surface on glass substrates. As the change ofreaction conditions，surface topography and crystalline types all changed. Under thecondition of120°C/6h, products had excellent surperhydrophobicity with very highwater contact angles, and the smallest sliding angles. Through the experiment, wefound that the surface can maintain superhydrophobic properties for4months in theindoor environment and delay the droplets freeze.(2) With potassium chlorate and manganese sulfate as raw materials, weprepared superhydrophobic γ-MnO2films with urchin-like structures on aluminiumsubstrates via a facile hydrothermal reaction method at150°C. The results of contactangle measurement showed that the modified γ-MnO2films exhibited extraordinarysuperhydrophobicity with a water contact angle of164.34°as well as a small slidingangle of5°. Utilized Cassie-Baxter equation, we calculated the actual contact area ofsolid and liquid. And the calculation result was only4.2%.(3) We have put more efforts into the study of the weather resistance, differentsuperhydrophobicities to solutions of different pH value, and icephobic property ofthe γ-MnO2films. We found that the surface can maintain superhydrophobicproperties for6months in the indoor environment The water droplets with different pH value were used to measure the contact angle on the surface. And the resultsshowed that the γ-MnO2films still keep nice hydrophobicity under these conditions.The contact angles were more than160°when the pH value of water droplets kept inthe range of3to13. We had observed the freezing process of water droplets on threekinds of substrates (pure aluminium, aluminium modified by stearic acid andsuperhydrophobic γ-MnO2surface) in the low temperature environment, and foundthat the water droplets on superhydrophobic γ-MnO2surface had the longest freezingtime. This means that superhydrophobic γ-MnO2surface has the function of delayingthe freeze time. Furthermore, the effect of the delaying is more obvious as the watervolume increased.