| Materials with special wettability have a wide application in daily life, industry and agriculture and have attracted attentions of researches.In the study, different surfaces with sepecial wettability were fabricated and characterized including a gecko-inspired superhydrophobic PDMS (polydimethylsiloxane) surface with dry adhesion and self-cleaning property, a superhydrophobic/superoleophilic oil-water separation copper mesh film and a oil-water separation mesh film with rapid reversible wettability between superhydrophobicity and superhydrophilicity. The surface properties and functional characteristics of the special wettable materials were studied in the study. The potential applications of the materials with special wettability were explored in dry adhesive and oil-water separation field. The main contents and conclusions in the study are summarized as follows.(1) A gecko-inspired superhydrophobic PDMS surface with dry adhesion and self-cleaning property was prepared and its adhesion property, wettability and self-cleaning property were studied. The effect of roughness and surface energy of counterface on the adhesion of gecko-inspired microfiber surfaces, superhydrophobicity, and wet self-cleaning were studied. The adhesion of gecko-inspired microfiber surfaces depended on the roughness of the counterfaces due to the influences of contact area and interlocking mechanism. SEM images revealed the matched and dis-matched interfaces between counterfaces with different roughness and gecko-inspired microfiber surfaces directly. The gecko-inspired microfiber surface got the larger adhesive force from the higher surface energy counterface, which is consisted with Johnson-Kendall-Roberts (JKR) theory. The smaller dimension and lower duty ratio of micro fibers on PDMS resulted in the increasing of Water Contact Angle (WCA) and the decreasing of Sliding Angle (SA) compared to those of smooth PDMS. Particularly, sample P-8-28-20 had the biggest WCA (155°) and SA (7°), which displayed the superhydrophobicity. Be similar to the feet of gecko, the microfiber surfaces appeared the ideal wet self-cleaning property. Quantitative test result showed that the self-cleaning efficiency of sample P-8-20-20 could reach 91.3%.(2) An oil-water separation copper mesh film with both superhydrophobic and superoleophilic properties were prepared by a facile myristic acid solution-immersion method. The wettability and oil-water separation performances of the as-prepared copper mesh films were characterized comprehensively. The most effective syhthetic conditions to obtain superhydrophobic and superoleophilic mesh film were discussed and optimized. The contact angle (CA) for water on the as-prepared mesh film was 156.7°, and for diesel oil 0°. It conjectured that the micro/nanostructured morphology on the copper mesh surface combined with the chemical composition contributes to the superhydrophobic and superoleophilic properties. The test results of EDS, FTIR and XRD confirmed that the chemical composition of the micro/nanostructure on the copper mesh surface was Cu[CH3(CH2)12COO]2.The micro/nanostructure and superhydrophobic/superoleophilic properties of as-prepared mesh film was kept stable after immersed into the solution of pH from 1.0 to 13.8, or 1.0 M NaCl solution for 72 h, respectively. The average intrusion pressure for water is 3.18 kPa. It indicated that water could not flow through the mesh film less than this pressure. The intrusion pressure of diesel oil is 0. Consequently, the as-prepared mesh film was capable of separating a large amount of oil-water mixtures. Mixtures of petroleum ether/water, n-hexane/water, diesel/water, and 1, 2-dichloroethane/water were successfully separated with high efficiency more than 98%. Almost no visible oil existed in the water after the separation. The separation efficiencies could keep above 97% after 100 cycle tests. In this study, this high separation efficiency and durability of oil and water had the promising applications further.(3) An oil-water separation copper mesh film with rapid reversible wettability between superhydrophobic/superoleophilic and under superoleophobic/superhydrophilic was successfully prepared by combining the modification of stearic acid and thermal oxidization. The wettability and oil-water separation performances of the as-prepared mesh films were characterized comprehensively. Firstly, a hierarchical CuO micro/nanostructure was built up on copper mesh film by immersing the original copper mesh into 2.5 M NaOH and 0.10 M K2S2O8 solution to oxidize for 20 min. The copper mesh film could be hydrophobized with the modification of 0.02 M stearic acid for 5 min, after which it turned into superhydrophobicity and showed a water contact angle as high as 161.6°. The intrusion pressure of water was above 1.2 kPa. The mesh film could also regain the superhydrophilicity with a zero water contact angel after annealing at 330℃ for 3 min, which was transformaed to the low surface energy CuO monolayer again on the surface. Repeating the process of chemical surface modification and annealing, it was successful to fulfill the wettability cycling between superhydrophobicity and superhydrophilicity on the copper mesh film. The wetting transition was realized by stearic acid modification and annealing rapidly in 8 min. The wetting behaviors transition mechanism was discussed based on the results of EDS, FTIR and XRD analysis. The chemical composition of the micro/nanostructure on the surface was Cu[CH3(CH2)16COO]2 after modification by stearic acid. After annealing at 330℃, Cu[CH3(CH2)16COO]2 was oxidized to form the CuO layer again. The oil-water separation efficiencies of copper mesh film to mixtures of petroleum ether/water, n-hexane/water,1,2-dichloroethane/water and diesel/water were more than 97% under both the superhydrophobilicity and superhydrophobicity state. The separation efficiencies still could keep high efficiency after 20 cycle tests. The as-prepared mesh films can selectively separate water or oil from oil/water mixtures with high separation efficiency and resistance stable structure and they were easy to recycle.The prepared materials with special wettability in this study presented favorable structural properties and functional characteristics, and had the potential applications in dry adhesion, self-cleaning and oil/water separation fileds. |
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