Zwitterionic copolymer additive architecture affects membrane performance: fouling resistance and surface rearrangement in saline solutions
Zwitterionic copolymer additive architecture affects membrane performance: fouling resistance and surface rearrangement in saline solutions
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DOI：
10.1039/c8ta11553b
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发表时间：
2019-03-07
影响因子：
11.9
通讯作者：
Asatekin, Ayse
中科院分区：
文献类型：
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作者：
Kaner, Papatya;Dudchenko, Alexander V.;Asatekin, Ayse
膜分离操作简单、可扩展、通用且节能，但由于进料组分沉积在膜表面上而导致的结垢或性能下降，限制了其更广泛的使用。用诸如两性离子的基团进行表面官能化可以减轻有机化合物的吸附，从而限制结垢。这可以通过在膜制造过程中使用表面分离共聚物添加剂来实现，但是需要更好地理解聚合物结构和构造如何影响这些添加剂在改善膜性能方面的有效性。在这项研究中，我们的目的是探讨的影响的结构的两性离子共聚物添加剂聚偏氟乙烯（PVDF）为基础的膜污染减轻和离子强度响应。我们从PVDF与两性离子（ZI）共聚物的共混物中制备了具有两种不同结构（无规和梳形）的膜。作为无规共聚物，我们使用自由基聚合法合成的聚（甲基丙烯酸甲酯-无规-磺基甜菜碱-2-乙烯基吡啶）（PMMA-r-SB2VP）。采用可控自由基聚合法，在PVDF主链上接枝SB2VP侧链，合成了梳形共聚物。膜由含有至多5重量%ZI共聚物的PVDF-共聚物共混物制成。与不含添加剂的PVDF膜相比，加入5重量%的任一共聚物，水渗透性增加了5倍。梳形共聚物添加剂导致更好的耐污垢的盐水油包水乳液和模拟蛋白质吸附在原子力显微镜（AFM）力测量。添加剂结构对膜如何响应进料盐度的变化具有显著影响，已知进料盐度影响两性离子聚合物中的分子内和分子间相互作用。含无规共聚物的膜的渗透率随盐度的增加而减小，且大部分是可逆的。相比之下，梳状共聚物的膜在盐溶液中进行构象重组，导致不可逆的渗透性降低，增加膜表面上的两性离子基团含量，和更光滑的表面形貌。梳形结构中两性离子基团的较高流动性促进两性离子侧链响应于离子强度的重组。总的来说，本研究建立了一种新的方法，用于开发高度耐污染的膜，并定义了一种两性离子共聚物添加剂的结构如何影响膜的离子强度响应和耐污染性。
Membrane separations are simple to operate, scalable, versatile, and energy efficient, but their broader use is curtailed by fouling or performance decline due to feed component depositing on the membrane surface. Surface functionalization with groups such as zwitterions can mitigate the adsorption of organic compounds, thus limiting fouling. This can be achieved by using surface-segregating copolymer additives during membrane manufacture, but there is a need for better understanding of how the polymer structure and architecture affect the effectiveness of these additives in improving membrane performance. In this study, we aim to explore the impact of the architecture of zwitterionic copolymer additives for polyvinylidene fluoride (PVDF)-based membranes in fouling mitigation and ionic strength response. We prepared membranes from blends of PVDF with zwitterionic (ZI) copolymers with two different architectures, random and comb-shaped. As the random copolymer, we used poly(methyl methacrylate-random-sulfobetaine-2-vinyl pyridine) (PMMA-r-SB2VP) synthesized by free radical polymerization. The comb-shaped copolymer was synthesized by grafting SB2VP side-chains from a PVDF backbone by controlled radical polymerization. Membranes were fabricated from PVDF-copolymer blends containing up to 5 wt% ZI copolymer. Compared to the additive-free PVDF membrane, water permeance increased five-fold with 5 wt% addition of either copolymer. The comb copolymer additive led to better resistance to fouling by a saline oil-in-water emulsion and to simulated protein adsorption in Atomic Force Microscopy (AFM) force measurements. The additive architecture had a significant influence on how membranes respond to changes in feed salinity, which is known to affect intra- and inter-molecular interactions in zwitterionic polymers. The random copolymer containing membrane showed a small and mostly reversible decrease in its permeance with salinity. In contrast, the comb copolymer-containing membrane underwent a conformational reorganization in saline solutions that leads to an irreversible permeance decrease, increased zwitterionic group content on the membrane surface, and smoother surface topography. The higher mobility of the zwitterionic groups in the comb-shaped architecture facilitates reorganization of the zwitterionic side-chains in response to ionic strength. Overall, this study establishes a new approach for developing highly fouling resistant membranes and defines how the architecture of a zwitterionic copolymer additive impacts the ionic strength response and fouling resistance of the membrane.