Fabrication And Properties Of Superhydrophobic PVDF Microporous Composite Membrane

In recent years,the membranes which used in gas-liquid membrane contactors such as membrane distillation,membrane absorption,membrane gas stripping and so on are required to have excellent hydrophobicity and self-cleaning performance,in order to prevent the membrane’s holes from being soaked and reduce surface contamination,thereby improving the separation efficiency and extend the service life of the membranes.Polyvinylidene fluoride(PVDF)has been widely used in the preparation of separation membranes because of its excellent physical and chemical properties.However,PVDF membranes still exist hydrophilic penetration,adhesion of pollutants and other issues in their practical applications.Therefore,improving the hydrophobicity and diminishing the adhesion of PVDF membrane become a key issue to be solved in this field.In this dissertation,a novel method is reported for fabricating superhydrophobic polyvinylidene fluoride(PVDF)microporous composite membrane.PVDF microporous membrane fabricated by phase inversion was the support membrane.Carbon nanotubes(CNTs)were deposited on the support membrane by constant pressure filtration,then the prepared membrane was coated with polydimethylsiloxane(PDMS).The resulted composite membrane exhibited superhydrophobic and low adhesion properties with water contact angle of 161.5° and sliding angle of 10.2°.The formation mechanisms of the super hydrophobic surface were investigated in terms of the effects of microstructures scales substrates,carbon nanotube and PDMS coating.It was revealed that the rough substrate had provided the micro-scale rough structure of PVDF membrane and increase the surface roughness of the membrane.The CNTs were deposited on a highly hydrophobic PVDF microporous membrane which has micron rough structures by constant pressure filtration.The addition of CNTs strengthens the nanostructures of the membrane surface and further improves the roughness of the membrane.The PDMS coating reduces the surface energy of the membrane effectively.Their synergistic effect increases the contact angle and decreases sliding angle of the composite membranes significantly.It was confirmed that the ability to achieve such super-hydrophobic and low adhesion performances was the result of the synergistic effect of rough substrates,CNTs and PDMS.The effects of the concentration of CNTs in the dispersions and PDMS in the coating solution,filtration pressure and surface coating time on the properties of the membranes were also investigated.On these bases,super hydrophobic PVDF microporous composite membranes were prepared with a low adhesion and a good permeability.The preparation conditions of membrane with excellent performance were summarized.