【作者】 蒋金泓；

【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， 2014， 博士

【摘要】 聚合物分离膜在当代膜分离技术领域中具有非常重要的地位,然而膜污染与由膜接触所引发的凝血、免疫排斥等问题严重制约了聚合物分离膜的进一步发展和在水处理、生物医用等领域的应用。探索聚合物分离膜的新型改性方法,对膜表面进行功能化设计,构建细胞亲和表面与抗凝血、抗污染和抗菌表面是解决聚合物分离膜所面临的各种问题的关键。基于贻贝仿生的聚多巴胺涂层／粒子的潜在反应性,本论文在深入研究多巴胺自聚与沉积行为的基础上,分别通过表面二次修饰构建了具有抗污染、抗菌与生物相容性的功能表面,以期为疏水性聚合物分离膜的表面修饰提供新的可能途径。本文首先研究了多巴胺在不同条件下的自聚-沉积行为及聚多巴胺(PDA)涂层的基本性质。基于多巴胺的自聚-附着特性,采用多巴胺水溶液对聚偏氟乙烯(PVDF)致密薄膜进行表面涂覆改性。由椭偏光谱仪和扫描电镜(SEM)观察结果得知,多巴胺的自聚和沉积速率随反应温度的升高而增大。且PDA涂覆改性前后PVDF膜的表面形貌、反应液中PDA粒子的外形与尺寸也分别采用SEM、原子力显微镜(AFM)和透射电镜(TEM)进行了观测。研究发现,改性膜的表面粗糙度和表面能主要受反应温度的影响,而与反应时间和多巴胺浓度的关系不大。此外,采用相同的方法对另外三种典型的疏水聚合物致密薄膜—聚四氟乙烯(PTFE)、聚对苯二甲酸乙二醇酯(PET)和聚酰亚胺(PI)进行表面改性,发现这些薄膜对液体的亲和性与表面能均得以显著提高,与PVDF膜的情况相似。该结果表明,聚合物膜的表面性质不会对PDA在其表面的沉积行为产生明显的影响。上述结果不仅有助于进一步理解PDA涂层的仿生特性,而且为开发PDA仿生的新型聚合物功能材料提供了有益的参考。基于聚多巴胺纳米粒子(PDA NPs)与PVDF基体之间的强粘合作用,本文利用非溶剂致相转化法(NIPS)制备了PVDF/PDA共混膜。PDA NPs的外形、尺寸和PVDF膜的表面形貌分别采用TEM和SEM进行了观测。水接触角测试结果表明,共混膜的亲水性较原膜有所增强。共混改性后,膜的通量和抗污染能力均得以明显提高。而拉伸实验证明,添加剂适量时还能够有效改善PVDF膜的韧性。此外,共混膜在水环境下表现出理想的长期稳定性。以共混膜中具有潜在反应性的PDA NPs为表面二次修饰的平台,将含溴基团的引发剂共价固定至共混膜表面,并通过磺基甜菜碱(SBMA)的原子转移自由基聚合反应(ATRP)在共混膜表面构建两性离子聚合物刷。改性对膜表面形貌的影响通过SEM和AFM进行了检测和分析。与原膜相比,改性膜的亲水性较原膜有较为明显的提升,其中接枝膜的抗污染性能大幅提高。体外实验表明,两性离子聚合物刷的引入有效抑制了血小板在膜表面的粘附和变性,显著改善了PVDF膜的血液相容性。PDA NPs的稳定性与反应性为共混膜提供了进一步表面功能化的平台,其大幅增强了聚合物膜表面的可设计性,为聚合物功能膜的构建开辟了新的思路。氧化条件下,置于多巴胺水溶液中的固体材料表面会逐渐生成一层紧密附着的PDA薄膜,该薄膜的粘附性与潜在反应性可以允许其通过二次处理的方法实现材料表面的功能化修饰。本文基于多巴胺的这一性质在聚丙烯(PP)膜表面构建了PDA涂层,然后通过多重氢键将聚乙烯吡咯烷酮(PVP)结合至膜表面。水接触角、油水分离实验、通量和抗污染性能测试结果表明,改性后,膜的亲水性和润湿性能得以显著改善,膜通量、抗污染能力和分离效率也有所提高。由于PDA与PVP涂层之间能够形成较强的非共价键相互作用,PVP改性的PP膜具有理想的耐久性。而且,将具有广谱抗菌活性的碘络合至PVP涂层后,还能够显著增强PP膜的抗菌活性。因由共价键结合的功能层具有更佳的长期稳定性,在另一部分工作中,首先基于多巴胺的自聚-附着特性在聚乙烯(PE)膜表面构建PDA涂层,并通过温和条件下的迈克尔加成或席夫碱反应,分别将肝素、牛血清白蛋白(BSA)固定至PE膜表面。由水接触角和通量测试结果得知,改性膜的亲水性较原膜有所改善,且在适当的改性条件下,膜的纯水通量也会明显提高。此外,肝素或BSA的引入大幅提高了PE膜表面的血液相容性,而PDA与BSA复合层还能显著改善PE膜的细胞相容性,但与BSA相比,细胞更倾向于在PDA涂层表面粘附和铺展。除聚合物膜之外,该方法还适用于其他固体材料的表面改性,且对材料的尺寸和形状均无限制。因此,该法为材料的表面功能化修饰和应用拓展提供了一种通用、有效的新手段。更多还原

【Abstract】 Polymer membranes play important roles in current separation and purification technologies. However, membrane fouling, blood coagulation and immunologic rejection resulting from contact with membranes limit their further developments and applications in water treatment, biomedical fields, and so on. It is clear that all these adverse effects are closely related to the poor hydrophilicity, biocompatibility and antimicrobial properties of the polymer membranes. A promising strategy for solving these problems may be construction of novel functional layers that could endow the membranes with improved performances. Recently, the bionic researchers have found that mussel-inspired polydopamine (PDA) could be incorporated into/onto materials on the basis of the self-polymerization and adhesion behavior of dopamine. PDA has good compatibility with various materials, and could serve as a versatile platform for surface functionalization via simple secondary treatments. In the present dissertation, the self-polymerization and deposition of dopamine on different substrates were systematically studied. Then PDA particles/films were incorporated into/onto polymer membranes by blending or surface modification process, and different functional layers based on PDA were designed to enhance the antifouling, antimicrobial properties and biocompatibility of the membranes. It is expected to establish a versatile approach of surface modification for hydrophobic polymer membranes.This study first explored the self-polymerization and deposition behavior of dopamine under different conditions and the fundamental surface characteristics of polydopamine (PDA) coatings. A poly(vinylidene fluoride)(PVDF) film was surface modified by dip coating in an aqueous solution of dopamine on the basis of its self-polymerization and strong adhesion feature. The self-polymerization and deposition rates of dopamine on film surfaces increased with increasing temperature as evaluated by both spectroscopic ellipsometry and scanning electronic microscopy (SEM). Changes in the surface morphologies of PDA-coated films as well as the size and shape of PDA particles in the solution were also investigated by SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The surface roughness and surface free energy of PDA-modified films were mainly affected by the reaction temperature and showed only a slight dependence on the reaction time and concentration of the dopamine solution. Additionally, three other typical hydrophobic polymer films of polytetrafluoroethylene (PTFE), poly(ethylene terephthalate)(PET), and polyimide (PI) were also modified by the same procedure. The liquid affinity and surface free energy of these polymer films were enhanced significantly after being coated with PDA, as were those of PVDF films. It is indicated that the deposition of PDA is not strongly dependent on the nature of the polymers. This information provides us with not only a better understanding of biologically inspired surface chemistry for PDA coatings but also effective strategies for exploiting the properties of dopamine to create advanced functional materials.Based on the strong adhesion effect between polydopamine nanoparticles (PDA NPs) and PVDF, a PVDF/PDA blend membrane was prepared via non-solvent induced phase separation (NIPS) process. The size and shape of PDA NPs as well as the surface morphologies of PVDF/PDA membranes were observed by TEM and SEM. Data of water contact angle measurements showed that the hydrophilicity of the blend membranes was improved obviously compared with that of the unmodified PVDF membrane. The water permeability and antifouling properties of the PVDF membranes were both enhanced after blending modification as evaluated by protein filtration tests. Results from tensile test indicated that an appropriate amount of PDA NPs was able to improve the toughness of the as-prepared blend membranes. Moreover, the PVDF/PDA blend membranes had satisfying long-term stability in aqueous environment. The PVDF/PDA blend membranes were able to undergo secondary treatments based on the potential reactivity of PDA NPs. Initiators containing Br groups were immobilized on the blend membranes via covalent conjugation with PDA. Then zwitterionic polymer brushes were incorporated onto the membranes through atom transfer radical polymerization (ATRP) of sulfobetaine methacrylate (SBMA). The surface morphologies of membranes before and after grafting were observed by SEM and AFM. The surface hydrophilicity of the modified membranes was remarkably improved by compared with the pure PVDF membrane. Experiments of protein filtration showed that membrane fouling obviously reduced after surface grafting. Results of platelet adhesion test indicated that the incorporation of poly SBMA suppressed the adhesion and activation of platelets, and improved the in vitro hemocompatibility of PVDF membranes significantly. The stability and reactivity of PDA NPs offer opportunities to realize surface functionalization of the blend membranes, which enhances their surface designability and allows effective development of novel functional polymer membranes.It is well-known that a tightly adherent PDA layer can be generated over a wide range of material surfaces through a simple dip-coating process in dopamine aqueous solution. The resulting PDA coating is prone to be further surface-tailored and functionalized via secondary treatments because of its robust reactivity. Herein, a typical hydrophobic polypropylene (PP) porous membrane was first coated with a PDA layer and then further modified by poly(N-vinyl pyrrolidone)(PVP) via multiple hydrogen-bonding interactions between PVP and PDA. Data of water contact angle measurements showed that hydrophilicity and wettability of the membranes were significantly improved after introducing PDA and PVP layers. Both permeation fluxes and antifouling properties of the modified membranes were enhanced as evaluated in oil/water emulsion filtration, protein filtration, and adsorption tests. The PVP layer immobilized on the membrane had satisfying long-term stability and durability because of the strong noncovalent forces between PVP and PDA coating. Furthermore, the modified membranes showed remarkable antimicrobial activity after iodine complexation with the PVP layer. In the other work, a functional layer was immobilized onto PDA-coated membranes via covalent bonding with better long-term stability. A thin PDA layer was first formed and tightly coated onto PE membranes by dipping simply the membranes into dopamine aqueous solution for a period of time. Subsequently, heparin or bovine serum albumin (BSA) was bound onto the PE/PDA composite membranes via Michael-type addition or Schiff base reaction. The results of water contact angle measurement showed that the hydrophilicity of PE membranes was significantly improved after modification. And the water flux of the modified membranes increased under proper modification conditions. Moreover, the heparin or BSA-immobilized PE membranes had better blood compatibility than the unmodified PE and the PE/PDA composite membranes. The PDA and BSA layers endowed PE membranes with significantly improved cell compatibility. Compared to BSA surface, PDA surface is more favorable for cell adhesion, growth, and proliferation. The strategy of material surface modification is substrate-independent, and applicable to a broad range of materials and geometries, which allows effective development of materials with novel functional layers based on the mussel-inspired surface chemistry.更多还原