Functional Modification Of Biomimetic Superhydrophobic Materials

In recent years,plenty of creatures with special wettabilities in nature have been extensively studied,including self-cleaning superhydrophobic lotus leaves and high adhesion superhydrophobic rose petals.As a functional wetting behavior,bioinspired superhydrophobicity has attracted the amounts of attentions.However,superhydrophobic materials are also limited to some chanlleges.Firstly,due to the strong water repellency,it is often difficult to accomphilish further functional modifications on non-wetting surfaces.Secondly,the microstructures and chemical compositions that contribute to superhydrophobic surfaces are extremely unstable,so how to ensure the surface mechanical and chemical stability is the key factor for its abroad application.Compared with the single wetting of superhydrophobicity,the preparations of surfaces with multiple superwettabilities,such as reversible responsive superwettability between superhydrophobicity and superhydrophilicity,gain greater applied potentials.Based on these,we mainly discussed the researchs related to functionalized modification on bioinspired superhydrophobic substrates at macro and micro scales,then constructing a variety of functional materials with special wettabilities.A simple and quick prewetting method was used to prepare regular hydrophilic patterns on the Cassie superhydrophobic substrates.First,dichloromethane(DCM)was used to prewet Cassie superhydrophobic copper sheet,and then the mussel inspired hydrophilic biological adhesive dopamine(DA)solution was added to the above surface,where the minimum volume of DA could be controlled at 0.1?L.After the evaporation of DCM and the self-polymerization of DA,hydrophilic polydopamine regions were constructed on the superhydrophobic sample,thus obtaining hydrophilic/superhydrophobic patterned materials similar to desert beetles'backs.In the field of water collection,it was found that the highest water collection efficiency was5.5±0.2 mg/min^-1/cm^-2 when the percentage of hydrophilic area was 8.0%.This pre-wetting method could also prepared macroscopic hydrophilic points on a variety of superhydrophobic substrates(Cu wire,Fe sheet,Al sheet,fabric,Cu mesh,and Ni foam).This study provides an effecitive method for rapidly fabricating macroscopic hydrophilic patterns on superhydrophobic surfaces,which greatly expands the large-scale application of water-collecting materials in real-world.Inorganic-organic superhydrophobic paint was prepared by mixing the superhydrophobic titanium dioxide(TiO₂)with epoxy resin(ER),which solved the problems of low mechanical properties,easy chemical corrosion and UV sensitivity on the water-repelled TiO₂-based coating.Due to epoxy resin coated on TiO₂ nanoparticles,the composited paint displayed multifunctional properties.The mechano-chemical robustness of ER ensured the mechanical stability and chemical corrosion resistance on the coating.Meanwhile,it also showed self-healing,anti-icing,high temperature(150?),liquid nitrogen(-196?)and self-cleaning.When exposed to UV light,the fluorosilane-TiO₂ coating would lose the superhydrophobic properties.However,the ER-coated TiO₂ surface exhibited strong UV resistance.Even under UV light(365 nm,5.0±0.6 m W/cm²)for 100 hours and outdoor sunshine for 8640 hours(1 year),the coating surface can still maintain super water-repellency.Because of the presence of titanium dioxide,photocatalysis was still found on our coating.The multifunctional superhydrophobic paint can also be applied to the grass house to protect its surface from being wetted by rainwater,which will provide significant practical value for the waterproof house in underdeveloped areas.In complex application systems nowadays,single superhydrophobicity is often unable to meet the diverse practical requirements,so the preparation of responsive superwetting material is a more popular topic.Responsive superwetting paint was prepared by mixing quantitative dual-size TiO₂ nanoparticles(21 nm and 200 nm),fluorosilane,epoxy resin,polyethylene glycol(PEG),and N-isopropylacrylamide(PNIPAM)into ethanol solution.The paint can be coated on five substrates,such as Al plate,fabric,glass slide,filter paper,and dish,and all of them showed reversible superwetting responsiveness.When the temperature is greater than 28?,the coating manifested(super)hydrophobicity,when the temperature is less than 28?,it was(super)hydrophilic.The reversible superwettability still remained even after the mechanical destructions of sandpaper abrasion,knife-scratching,and finger-wipe.Although fluorinated TiO₂ owns photoresponsive wettability,wettability of the coating was not sensitive to UV light,whereas,it showed excellent UV resistance.After 50 h UV irradiation(365 nm,5.0±0.6 m W/cm²),the coating surface still exhibited stable temperature induced reversible transformation of superhydrophobicity and superhydrophilicity.The coating surface showed wetting changes during the temperature change process,at the same time,the contact lines or contact areas between the droplets and the surfaces differed in vaired temperature accordingly.For the degradation of water-base dyes,the contact line or contact area is the key point to control the photodegradation efficiency on the coating surface.At low temperature(10?),the degradation efficiency for methylene blue(MB)solution on the coating is the highest(95.5%).At high temperature(50?),the degradation efficiency for MB earned a lowest value of 15.0%.