Preparation And Properties Of Vertically-Oriented Membranes Via Crystal Template Method

Porous polymer membrane prepared by melt stretching and phase separation generally suffers from large pore size polydispersity and tortuous channels.The resultant membranes show low separation accuracy and large transmembrane resistance.Vertically-oriented polymer membranes(VOPMs)have received great attention for the narrow pore size distribution,straight-through pores,and low transmembrane resistance.Preparation methods for VOPMs include track etching,anodization,lithographic microfabrication,self-assembly,and microphase separation of block copolymers.Crystal template method is a new route for VOPM,which has the advantages of simple steps,easy control of pore structure,and good universality.In this thesis,small organic molecules with high melting point were used as templates,and PS and PL A VOPMs were fabricated via bidirectional freezing crystal template method.The influences of polymer concentration and temperature gradient were investigated.The applications of VOPM were also demonstrated.Our specific studies are as follows.For polystyrene/diphenylsulfone(PS/DPS)system,the interaction between different crystal planes of DPS and PS was simulated by Gaussian algorithm.Combined with the XRD data of the primary membrane powder,the dominant planes of DPS were influenced by the interaction between the different crystal planes of DPS and PS,affecting the nucleation and growth of DPS crystals.Two temperature gradients were determined along the y-axis and z-axis directions.SEM images showed that the membrane pore structure was affected by the temperature gradients.PS VOPM was further modified by PDA/PEI solution on single side and applied to oil-water separation,which showed large flux and better stability than the bicontinuous porous membrane.For poly(lactic acid)/dimethylsulfone(PLA/DMS02)system,VOPM was fabriceted,in which polymer concentration and water bath temperature were important factors.Silica nanoparticles were filtrated by VOPM.It was found that vertically-oriented pores can reduce pore blockage to some extent.Hydrophilic PL A VOPM modified by PDA/PEI was applied to oil-water separation.Compared to traditional membrane,VOPM showed higher flux and better anti-fouling property.