Preparation And Characterization Of Antifouling And Self-cleaning PVDF Membranes

Membrane material is known as the fifth building materials following glass,wood,cement and steel.Especially the application in the field of large-scale outdoor construction can solve the problem of large span,long construction period,poor lightingwhich can not be solved by the traditional building form.PVDF membrane was often used as a surface coating for architectural membranes,because it had some hydrophobic properties due to its low surface energy,but the hydrophobic properties is still far from meeting the requirements of antifouling and self-cleaning for architectural membrane materials in the environment.Based on the "lotus leaf effect" theory and solid surface wetting theory,this project achieved the performance of antifouling and self-cleaning by constructing rough structure like lotus leaf surface on polyvinylidene fluoride(PVDF)membrane surface and lower the membrane surface energy.Superhydrophobic and self-cleaning properties of membrane materials can not only reduce cleaning costs and hazard factors,but also bring huge economic and social benefits in terms of environmental protection and energy conservation.This project used the template method to prepare the PVDF membrane,achieving the construction of the membrane surface roughness structure by changing the roughness of the template;lowering membrane surface energy by adding fluororesins to PVDF membrane coating glue.The hydrophobicity and self-cleaning properties of the films were tested using the contact angle and the ash collection test.The effects of surface roughness and surface energy on the hydrophobicity of the films were analyzed by SEM and XPS.The results showed that the surface of PVDF membrane prepared by the template method has a rough structure,the CA value is much larger than that of the flat membrane,and the hydrophobicity obviously increased.Compared with the same roughness condition.Compared with unblended PVDF membrane with the same roughness,the CA value increased by about 20 ° after adding 4#fluororesins.The better contact angle of PVDF membrane prepared by adding 4#fluororesins with 2#template is 155.34 °,and the membrane surface had micro and nano-scale convex structure,having showed good self-cleaning performance in ash-collection test.The surface roughness of the membrane was characterized based on the fractal theory.The box surface counting method and the surface area method were used tocalculate the fractal dimension of the membrane surface and the feasibility of using fractal dimension to characterize roughness of membrane surface was analyzed corresponding CA value.The results showed that the box counting method was not suitable for characterizing the membrane surface roughness,but the fractal dimension calculated by the specific surface area method was feasible to characterize the surface roughness of the membrane.The PVDF membrane prepared by 1#template with 4#fluororesins had good hydrophobicity and the surface fractal dimension is 2.608,which is similar to that of lotus leaf surface fractal dimension 2.74.The fractal dimension of the membrane surface decreases with the increase of the SEM image magnification in the overall trend,calculatation of the fractal dimension must be unified magnification under the premise.