Accessing greater thickness and new morphology features in polyamide active layers of thin-film composite membranes by reducing restrictions in amine monomer supply
Accessing greater thickness and new morphology features in polyamide active layers of thin-film composite membranes by reducing restrictions in amine monomer supply
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DOI：
10.1016/j.memsci.2021.120112
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发表时间：
2022-02-15
影响因子：
9.5
通讯作者：
Coronell, Orlando
中科院分区：
文献类型：
--
作者：
Grzebyk, Kasia;Armstrong, Mikayla D. D.;Coronell, Orlando
薄膜复合材料（TFC）膜制造过程中通过界面聚合（IP）形成的聚酰胺被认为是自限制性的--从这个意义上说，聚酰胺膜在形成时限制了其自身的生长。在IP期间，均苯三甲酰氯（TMC）和间苯二胺（MPD）快速反应以形成初始聚酰胺膜，该初始聚酰胺膜致密化并减缓更可渗透的单体（MPD）的扩散，从而限制聚酰胺生长并产生通常表现出厚度< 350 nm的膜。这些聚酰胺膜的形态特征在于空隙结节状和叶状特征的基底层，其有时被重叠平坦特征的次级层覆盖。在这里，我们提出的证据表明，聚酰胺活性层是基本上可渗透的MPD，并尽量减少某些限制，在IP期间的MPD供应条件可以导致聚酰胺活性层的厚度比那些通常在文献中报道的几倍大（> 1 μ m）。除了表征典型聚酰胺活性层的空隙结节特征的基底层和重叠平坦特征的次级层之外，较厚的膜还表现出三种另外的形态特征：基底层或其他空隙特征顶上的毯状层、多层空隙结构和/或空隙巨型结节（直径高达超过1微米）。总之，结果表明，在IP期间减少MPD供应条件的限制：（1）克服了在常规TFC膜制造中观察到的有限聚酰胺生长，和（2）导致具有更突出的空隙结构的膜形态。后一种观察结果与最近描述CO2脱气和纳米气泡限制在聚酰胺活性层形态发展中的作用的文献一致。未来的研究可以改变MPD供应条件作为一种新的工具，以扩大活性层铸造中可实现的厚度范围，调节活性层形态，并优化独立于MPD供应的纳米气泡限制条件。这种能力可以帮助开发新的支持和TFC结构。
Polyamide formation, via interfacial polymerization (IP) during thin-film composite (TFC) membrane fabrica-tion, is regarded as self-limiting-in the sense that the polyamide film limits its own growth as it forms. During IP, trimesoyl chloride (TMC) and m-phenylenediamine (MPD) react rapidly to form an incipient polyamide film that densifies and slows the diffusion of the more permeable monomer (MPD), thereby limiting polyamide growth and yielding films that typically exhibit thicknesses < 350 nm. The morphology of these polyamide films is characterized by a basal layer of void nodular and leaf-like features that is sometimes overlaid by a secondary layer of overlapping fiat features. Here, we present evidence showing that polyamide active layers are sub-stantially permeable to MPD, and that minimizing certain restrictions in the MPD supply conditions during IP can result in polyamide active layers of thicknesses several times greater (> 1 mu m) than those typically reported in the literature. In addition to the basal layer of void nodular features and secondary layer of overlapping fiat features that characterize typical polyamide active layers, the thicker films also exhibited three additional morphological features: blanket-like layers atop the basal layer or other void features, multi-layer void structures, and/or void mega-nodules (up to over a micron in diameter). Overall, the results indicate that reducing restrictions in the MPD supply conditions during IP: (1) overcomes the limited polyamide growth observed in conventional TFC membrane fabrication and (2) leads to film morphologies with a more prominent void structure. This latter observation is consistent with recent literature describing the role of CO2 degassing and nanobubble confinement in the development of polyamide active layer morphology. Future studies could vary MPD supply conditions as a new tool to expand the range of achievable thicknesses in active layer casting, regulate active layer morphology and optimize nanobubble confinement conditions independently of MPD supply. Such capabilities could aid in the development of novel supports and TFC structures.