【作者】 朱丽静；

【导师】 徐又一； 朱利平；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2013， 博士

【摘要】 膜技术是一项新型高效的分离技术,被认为是解决人类所面临的资源和环境领域重大问题的共性技术之一,被广泛应用于污水处理、海水淡化、食品饮料纯化、生物医用过滤、化工分离等领域。膜材料是膜技术的核心,目前绝大多数膜技术依赖于有机高分子膜。与纯有机膜相比,聚合物基有机-无机复合膜结合了有机膜和无机膜的优势,表现出更加优异的分离透过性能和抗污染能力,正成为膜材料领域的研究热点之一。然而,无机纳米材料在聚合物基体中常常难以均匀分散,有机与无机两相之间结合不够紧密,导致无机纳米材料在膜服役过程中容易流失,起不到稳定持久的效果,这成为有机-无机复合膜进一步发展应用的主要障碍。在本论文的研究工作中,采取两种策略解决上述问题：(1)采用过滤沉积的方式将分散在液体中的有机-无机杂化纳米线复合在聚合物基膜表面,制备有机-无机复合膜,有机与无机两相仅通过聚合物膜表面相互接触,从而回避了两相之间的相容性问题和无机相团聚问题；(2)采用可逆加成-断裂链转移(RAFT)自由基聚合的方法,在无机纳米粒子表面接枝聚合物,制备有机-无机杂化纳米粒子,再将其与成膜聚合物溶液共混,制备有机-无机复合膜,聚合物接枝层的引入可有效抑制无机纳米粒子的团聚行为,显著增强无机纳米粒子与聚合物基体之间的相互作用,提高无机纳米粒子在聚合物基体中的稳定性。通过溶液生长的方法,在硝酸铜和乙醇胺形成的弱碱性溶液中制备了荷正电的单分散的氢氧化铜(Cu(OH)2)纳米线,再加入一定量的荷负电的肝素(Hep)溶液,Hep通过静电作用负载在Cu(OH)2纳米线表面,生成了Hep@Cu(OH)2有机-无机杂化纳米线。采取过滤沉积的方法,将Hep@Cu(OH)2杂化纳米线复合到聚砜(PSf)多孔膜表面,制备PSf/Hep@Cu(OH)2有机-无机复合膜。研究结果表明,Cu(OH)2纳米线表面负载的Hep量对复合膜的结构和性能有很大影响。当Hep的负载量为65.9μg/cm2左右时,水接触角测量结果显示复合膜具有优异的亲水性；当Hep的负载量达到212.0μg/cm2左右时,复合膜的水通量大于PSf基膜；当Hep的负载量达到408.4μg/cm2左右时,复合膜的水通量达到最大值约为517.2Lm-2h-1。Hep的负载有效地提高了膜的抗血小板粘附能力,而且复合膜对大肠杆菌(E.coli)和金色葡萄球菌(S. aureus)具有良好的抗菌能力。为了提高二氧化硅(SiO2)纳米粒子在聚醚砜(PES)基体中的分散性和稳定性及其与PES的相互作用,采用RAFT聚合方法,在Si02纳米粒子表面接枝聚甲基丙烯酸羟乙酯(PHEMA),制备了核壳结构的SiO2-g-PHEMA有机-无机杂化纳米粒子,将其作为添加剂,与PES溶液共混,通过传统的非溶剂诱导相分离法(NIPS)制备PES/SiO2-g-PHEMA有机-无机复合膜,考察了SiO2-g-PHEMA杂化纳米粒子的添加量对复合膜结构与性能的影响。研究结果表明,SiO2-g-PHEMA杂化纳米粒子能够很好的分散在铸膜液体系中,与PES表现出良好的相互作用；在膜/浴界面能最低化的驱动下,SiO2-g-PHEMA杂化纳米粒子在NIPS成膜过程中向膜表面迁移/富集,显著提高了PES膜的亲水性、抗污染和抗血小板粘附能力。当SiO2-g-PHEMA杂化纳米粒子的添加量从0增加到6wt%时,膜的水通量和牛血清白蛋白(BSA)截留率均得到明显提高,打破了超滤膜改性中常常出现的通量与截留率此消彼长、相互抑制的现象。由于PHEMA接枝链与PES链段之间的相互缠结和氢键相互作用,SiO2-g-PHEMA杂化纳米粒子在PES膜表面和本体中表现出良好的稳定性。为了实现有机-无机复合膜表面的进一步功能化,通过分子设计,采用RAFT聚合方法,在SiO2纳米粒子表面接枝具有反应活性的聚甲基丙烯酸二甲氨乙酯(PDMAEMA),制备了核壳结构的SiO2-g-PDMAEMA有机-无机杂化纳米粒子,并将其作为添加剂,通过NIPS法制备PES/SiO2-g-PDMAEMA有机-无机复合膜。研究结果表明,SiO2-g-PDMAEMA杂化纳米粒子不仅在铸膜液中分散性良好,而且在成膜过程中向膜表面富集,增强了SiO2-g-PDMAEMA杂化纳米粒子对改性膜亲水性和透水性的贡献,提高了SiO2-g-PDMAEMA杂化纳米粒子的利用效率。且由于PDMAEMA与PES聚合物链段之间的缠结作用,SiO2-g-PDMAEMA杂化纳米粒子在PES膜表面和本体中表现出良好的稳定性。更为重要的是,膜表面富集的反应性PDMAEMA链为膜表面的进一步修饰提供了反应性平台。分别采用1,3-丙磺酸内酯(1,3-PS)和碘甲烷(CH3I)与PDMAEMA进行季铵化反应,得到了两性离子化和阳离子化的膜表面。两性离子化的膜表面表现出优异的亲水性能和抗污染能力,阳离子化的膜表面对E.coli和S. aureus具有优良的抗菌能力。为了进一步提高Si02纳米粒子在聚偏氟乙烯(PVDF)基体中的分散性和稳定性以及有机与无机两相间的相互作用,进一步设计并通过AFT聚合在SiO2纳米粒子表面接枝聚甲基丙烯酸甲酯(PMMA)和PDMAEMA的两嵌段共聚物,得到核壳结构的SiO2-g-(PMMA-b-PDMAEMA)有机-无机杂化纳米粒子,将其与PVDF溶液共混,通过NIPS法制备PVDF/SiO2-g-(PMMA-b-PDMAEMA)有机-无机复合膜。研究发现,SiO2-g-(PMMA-b-PDMAEMA)杂化纳米粒子在PVDF基体中具有优异的分散性,能够显著地促进膜孔结构的形成和发展,提高膜的表面亲水性,添加较低含量(2.5wt%)的粒子还可以有效地提高PVDF膜的力学强度。且与SiO2-g-PDMAEMA杂化纳米粒子相比,SiO2-g-(PMMA-b-PDMAEMA)杂化纳米粒子在PVDF膜中具有更好的稳定性。进一步通过1,3-PS与PDMAEMA之间的季铵化反应,得到表面两性离子化的有机-无机复合膜,显著提高了PVDF膜的亲水性、抗污染性能和BSA截留率。综上所述,通过有机-无机杂化纳米粒子/线的分子设计,有效地提高了有机-无机复合分离膜的综合性能,为通用聚合物膜材料的改性与高性能化提供了理论和方法指导。更多还原

【Abstract】 As a new and highly efficient separation technology, membrane technology is considered as one of universal technique to solve important problems in the fields of resources and environments. Actully, membrane process has been widely used in wastewater treatments, seawater desalination, food and beverage purification, biomedical separation, chemical filtration etc. Basically, membrane material is thought the core of membrane technology. Nowadays, organic polymer membranes play a dominating role in most membrane technologies. Compared with neat polymeric or inorganic membranes, polymer-based organic-inorganic composite membranes often combine the advantages of both polymeric and inorganic membranes, and show more excellent separation performance and antifouling ability. The organic-inorganic composite membranes are attracting increasing attention in the field of membrane technologies. However, some problems and disadvanatages are still exisited for available organic-inorganic composite membranes. The inorganic nanomaterials are often difficult to disperse homogenously in polymer matrix, resulting in the occurance of defects in membrane. Moreover, the inorganic nanomaterials are easy to leach out during membrane application due to the poor miscibility and interaction between organic and inorganic phases. As a result, membrane performance might gradually degrade in membrane use. These problems have becoming the major obstacles of furture development and popularity of organic-inorganic composite membranes.In this thesis, we present two strategies to solve the above-mentioned problems. In the first strategy, a filtration and deposition route was used to prepare organic-inorganic composite membranes. The hybrid nanostrands well dispersed in water were filtrated and deposited onto polymer membrane and formed a hybrid separation layer. In this route, the nanostrands only contacted with the surfaces of polymer membranes. So the agglomeration of the nanostrands in the polymer matrix and the miscibility between two phases can be avoided. In the second strategy, polymer brushes were grafted from inorganic nanoparticle surfaces via surface-initiated reversible addition fragmentation chain transfer (RAFT) polymerization and obtained the organic-inorganic hybrid NPs. Then the organic-inorganic composite membranes were prepared from the blending solutions of polymer and the synthesized hybrid nanoparticles. The agglomeration of the nanoparticles in the polymer matrix can be effectively suppressed and the interaction between these two phases and the stability of the nanoparticles can be remarkably improved.First, the monodisperse positively charged Cu(OH)2nanostrands were prepared in a weakly alkaline copper nitrate solution in the presence of2-aminoethanol. Then a certain amount of negatively charged heparin (Hep) solution was added into the solution of nanostrands. The Hep was immobilized onto the surface of Cu(OH)2nanostrands by electrostatic interaction forming organic-inorganic hybrid Hep@Cu(OH)2nanostrands. The PSf/Hep@Cu(OH)2organic-inorganic composite membranes were prepared by filtration and deposition of the Hep@Cu(OH)2hybrid nanostrands onto a polysulfone (PSf) porous membrane surface. The results showed that the properties of the prepared composite membranes were highly affected by the amount of immobilized Hep on Cu(OH)2nanostrands. When the amount of immobilized Hep was about65.9μg/cm2, the water contact angles of the composite membrane indicated that the hydrophilicity of the composite membranes was best. When the amount of immobilized Hep was about212.0μg/cm2, the water flux of the composite membrane was more than that of the pure PSf membrane. Furthermore, when the amount of immobilized Hep was about408.4μg/cm2, the water flux of the composite membrane reached the maximum value. It was about517.2Lm-2h-1. The platelet adhesion resistant properties of the composite membranes were significantly improved by immobilizing Hep on membrane surface. In addition, the composite membranes exhibited very good antibacterial activities against Escherichia coli (E.coli) and Staphyloccocus aureus Rosenbach (5. aureus).In order to improve the dispersity and stability of silica nanoparticles (SiO2NPs) in PES and the interation between these two phases, the shell core SiO2-g-PHEMA organic-inorganic hybrid NPs were prepared by grafting poly(2-hydroxyethyl methacrylate)(PHEMA) brushes from SiO2NPs surfaces via RAFT polymerization. Then the PES/SiO2-g-PHEMA organic-inorganic composite membranes were fabricated from the blending solutions of polyethersulfone (PES) and the additive of SiO2-g-PHEMA hybrid NPs via the non-solvent induced phase separation (NIPS) process. The effects of SiO2-g-PHEMA hybrid NPs concentration on the structures and properties of the prepared composite membranes were mainly discussed. The results showed that the obtained SiO2-g-PHEMA hybrid NPs well dispersed in casting solution. The well dispersed SiO2-g-PHEMA hybrid NPs tended to migrate toward the membrane top surfaces under the driving force of minimization of interfacial energy between membrane and coagulation bath. The membrane hydrophilicity, antifouling and platelet adhesion resistant properties were significant improved caused by the enriched SiO2-g-PHEMA hybrid NPs on the membrane surface. When the concentration of SiO2-g-PHEMA hybrid NPs was increased from0to6wt%, the water permeability and the BSA rejection of the corresponding composite membranes increased simultaneously. The phenomenon indicated that the trade-off between permeability and selectivity of traditional ultrafiltration membranes was broken. The SiO2-g-PHEMA hybrid NPs had good stability in/on PES membrane due to the intertwisting and hydrogen bonds of polymer chains between PHEMA and PES.In order to achieve further functionalization of the organic-inorganic composite membranes, based on the molecular design, the shell core SiO2-g-PDMAEMA organic-inorganic hybrid NPs were prepared by grafting reactive poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) brushes from SiO2NPs surface via RAFT polymerization. Then the PES/SiO2-g-PDMAEMA organic-inorganic composite membranes were fabricated from the blending solutions of PES and the additive of the obtained SiO2-g-PDMAEMA hybrid NPs via the NIPS process. The results showed that well dispersed SiO2-g-PDMAEMA hybrid NPs tended to migrate toward the membrane top surfaces. Therefore, the contributions of SiO2-g-PDMAEMA hybrid NPs to the hydrophilicity and water permeability of the membrane were significantly improved. The efficiencies of the SiO2-g-PDMAEMA hybrid NPs were increased. In addation, the SiO2-g-PDMAEMA hybrid NPs showed well stability in/on PES membrane due to the intertwisting of polymer chains between PDMAEMA and PES. More importantly, the reactive PDMAEMA chains enriched on membrane surface provided a strategy to further surface modification. On one hand, the composite membranes were transformed into surface-zwitterionic composite membranes by quaternization between7,3-propane sultone (7,3-PS) and PDMAEMA. On the other hand, the composite membranes were transformed into cationic composite membranes by quaternization between methyl iodide (CH3I) and PDMAEMA. These membranes exhibited better hydrophilicity. It was confirmed that the surface-zwitterionic composite membranes had well antifouling abilities and the cationic composite membranes exhibited high antibacterial activities against E.coli and S. aureus.In order to further improve the dispersity and the stability of SiO2NPs in/on poly(vinylidene fluoride)(PVDF) matrix and the interaction between these two phases, based on the molecular design, poly(methyl methacrylate)(PMMA) and PDMAEMA brushes were serially grafted from SiO2NPs surface via RAFT polymerization forming the shell core SiO2-g-(PMMA-b-PDMAEMA) organic-inorganic hybrid NPs. Then the PVDF/SiO2-g-(PMMA-b-PDMAEMA) organic-inorganic composite membranes were fabricated from the blending solutions of PVDF and the additive of the obtained SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs via the NIPS process. The results showed that the SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs well dispersed in the PVDF matrix and significantly enhanced the formation and the development of membrane pores and the hydrophilicity. When the concentration of SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs was lower (2.5wt%), the tensile strength was higher than that of the pure PVDF membrane. Moreover, the SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs had better stability in/on PVDF membrane than that of SiO2-g-PDMAEMA hybrid NPs. The composite membranes were transformed into surface-zwitterionic composite membranes by quaternization between1,3-PS and PDMAEMA. It was confirmed that the surface hydrophilicity, antifouling ability and BSA rejection of the PVDF membranes were significantly enhanced after surface zwitterionicalization.In summary, the comprehensive properties of the polymer-based organic-inorganic composite separation membranes were significantly improved by molecular design of organic-inorganic hybrid nanoparticles/nanostrands used in membrane fabrication. The present work provides us with some useful academic and technological information on the modification and functionalization of commonly-used polymer separation membranes.更多还原