Study On Microstructure Construction And Performance Of Highly Stable Underwater Superoleophobic Surfaces

Recently,underwater superoleophobic surface have been extensively researched due to their promising applications in various areas such as antifouling coatings,oil/water separation,and oil droplet manipulation in microfluidics.Studies revealed that the underwater superoleophobicity derives from the combination of hierarchical micro/nanostructures and hydrophilic surface composition.According to this finding,a large number of artificial underwater superoleophobic surfaces have been prepared.Nevertheless,most of these surfaces easily lose their underwater superoleophobicity in practical applications due to their low mechanical stability.Surfaces with a robust underwater superoleophobicity is necessary to meet requirements for practical use.In this paper,several strategies are proposed for the design and fabrication of robust underwater superoleophobic materials,and the application of robust underwater superoleophobic materials in the field of oil/water separation is also studied.Three underwater low adhesive superoleophobic copper surfaces with hemispheric,pinecone-like,and honeycomb microstructure shapes,respectively,are prepared through an electrodeposition process.The oil contact angles(OCA)and the oil sliding angles(OSA)for all these surfaces in water are greater than 160° and less than 2°,respectively.After a series of damage experiments,one can find that the surface with the hemispheric microstructure has an excellent mechanical stability of the microstructure and a robust low adhesive underwater superoleophobicity.Under the same condition,the microstructures on the orther two surfaces are destroyed,and menwhile,the low adhesive underwater superoleophobicity is vanished.Detailed theoretical analysis indicates that the low adhesive underwater superoleophobicity is ascribed to the combined effect of the hierarchical structure and the intrinsic hydrophilicity of copper,and different mechanical stabilities are ascribed to different stress distributions on these microstructures under an external force due to different microstructure shapes.Furthermore,by using the same design strategy,a robust underwater superoleophobic oil/water separation copper mesh film is also prepared,the film exhibit excellent separation properties,with the separation efficiencies,the intrusion pressure,and theflux being higher than 99.9%,1.0 k Pa,and 80 000 L/m2·h,respectively.A robust underwater superoleophobic ADP/Cu surface is prepared through dip coating and heat treatment of a layer of rigid aluminum dihydrogen phosphate(ADP)on the existing fragile copper micro/nanostructure.SEM results and the mechanical wear tests results demonstrate that the ADP coating can act as a layer of “nano-armor” to protect the inner microstructure without changing its morphology,as a result,the stability of both surface microstructure and corresponding underwater superoleophobicity are improved remarkably.Specifically,the hardness of surface is improved by a factor about 10.Theoretical simulations analysis reveals that the enhanced effect results from the nanocoating,the maximum transverse deformation of microstructure before and after coating of ADP are about 32.5 nm and 12.8 nm,and the maximum stress on the microstructure is also significantly decreased from 227.2 MPa to153.5 MPa.Finally,the method was also applied on some other surfaces with particular functions including anisotropic wettings and oil/water separating properties.In view of the fact that inorganic underwater superoleophobic surface is easy to break and lost the underwater superoleophobicity in the state of bending or stretching,a stretchable underwater superoleophobic PU/Si O2 surface is prepared by introduction hydrophilic Si O2 nanoparticles into elastic polyurethane(PU)substrate.The hydrophilicity of Si O2 nanoparticles and good elastic recovery property of polymer matrix PU,endowing the underwater superoleophobic PU/Si O2 surface with excellent mechanical stability,even after a series of mechanical wear,press(2 MPa,20 times)and stretching(even the deformation reach 200%)it still keeps the surface morphology and underwater superoleophobicity unchanged.Meanwhile,the PU/Si O2 surface can maintain the low adhesive underwater superoleophobicity in the stretching state within a certain amount of deformation.The outstanding underwater superoleophobicity of PU/Si O2 surface derives from the combination of hierarchical micro/nanostructures and the intrinsic hydrophilicity of Si O2.The excellent resilience of the elastic PU endows the surface with special crushing resistance and strecting resistance.