Preparation And Properties Of Superhydrophobic Membrane Distillation Based On PDMS Graft Copolymer

The scarcity of fresh water resources has become a global environmental problem,At the same time,The vast amount of sea water resources on the surface of the earth which could not be used for human production and life due to their high salinity.Seawater desalination is undoubtedly one of the best way to provide sustainable freshwater resources.As a high separating efficiency,low capital cost,low-temperature,and low-pressure membrane-based process,membrane distillation(MD)has a promising future in seawater desalination,especially when low-grade thermal energy can be used to provide heat.However,Separation membranes still have some problems such as insufficient hydrophobicity,membrane fouling and membrane wetting hinder the industrialization development of membrane distillation technology.Inspired by the lotus leaf with superhydrophobic property resulting from the cooperation of hydrophobic wax-like material and hierarchical surface structures,In this paper,Surface coating method and covalent grafting method were used to modify the traditional hydrophobic membrane,Scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),capillary flow pore size analyzer and contact angle meter were used to characterize the surface morphology,chemical composition and hydrophobicity of the composite membrane.The composite membrane was applied to direct contact membrane distillation desalination.The effects of flux,stability and anti wetting of the membrane were investigated Performance.In this study,PDMS graft copolymer(PMMA-g-PDMS)was prepared by free radical polymerization.PDMS graft copolymer was used as hydrophobic modifier to modify PVDF membrane.The influence of the concentration of the modified solution on the structure and properties of the modified membrane was investigated.The results show that the performance of the modified membrane is the best when the concentration of PDMS graft copolymer is 8%.The average pore diameter of the modified membrane is about 0.66?m,and the contact angle between the surface and water is 149.38°.Through a series of comparison of membrane distillation experiments,the membrane shows good stability.The hydrophobicity of the membrane and the anti wetting ability in the process of membrane distillation are significantly improved by coating the modifier.In order to further improve the hydrophobic performance of the polyvinylidene fluoride membrane,it can achieve a super-hydrophobic surface.The covalent grafting method was used to graft nano-Si O₂on the surface of the PVDF base film to increase the roughness,and then a layer of PDMS graft copolymer with low surface energy was coated on the surface of the film to improve the mechanical stability of the composite layer.Finally,a Si O₂/PMMA-g-PDMS superhydrophobic composite layer was successfully constructed on the surface of the membrane.The results show that the contact angle of the composite membrane reaches 157.5°.Through a series of direct contact membrane distillation(DCMD)experiments,the superhydrophobic composite membrane has better anti-pollution and anti-wetting characteristics than the original membrane.