The formation of nodular structures in the top layer of ultrafiltration membranes
The formation of nodular structures in the top layer of ultrafiltration membranes
复制标题
超滤膜顶层结节结构的形成
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
C. A. Smolders
中科院分区：
文献类型：
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作者：
I. Wienk;T. V. D. Boomgaard;C. A. Smolders
考虑了超滤膜顶层形成的结节状结构。对文献中描述的机制进行了批判性的回顾。将聚合物溶液在非溶剂介质中混凝，制备了平板聚醚砜膜和中空纤维聚醚砜/聚乙烯吡咯烷酮膜。从这些实验中，发现了一些经验规则来描述顶层的最终形态。提出了一种新的球状结构形成机理。它是基于聚合物分子的扩散系数比溶剂和非溶剂的扩散系数小，并结合聚合物网络的高度纠缠。对于不稳定的组分，相分离将随着浓度波动幅度的增大而进行。在顶层，溶剂与非溶剂的快速扩散交换导致形成结核的浓度波动最大值的玻璃化。结核之间的聚合物链没有完全解开，这解释了超滤膜的小孔和低孔隙率。
The formation of nodular structures in the top layer of ultrafiltration membranes is considered. A critical review of mechanisms described in the literature is given. Flat-sheet poly(ether sulfone) membranes and hollow-fiber poly(ether sulfone)/polyvinylpyrrolidone membranes were made by coagulation of a polymer solution in a nonsolvent medium under different circumstances. From these experiments, a number of empirical rules are found to describe the resulting morphology of the top layer. A new mechanism for the formation of a nodular structure is proposed. It is based on the small diffusion coefficient of the polymer molecules compared to the diffusion coefficient of solvent and nonsolvent combined with a high degree of entanglement of the polymer network. For unstable compositions, phase separation will proceed by growth in amplitude of concentration fluctuations. The rapid diffusional exchange of solvent for nonsolvent in the top layer leads to vitrification of the maxima of the concentration fluctuations that form the nodules. Complete disentanglement of the polymer chains between the nodules is not reached, which explains the small pores and the low porosity of ultrafiltration membranes.