Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States.
Langmuir. 2017 Sep 12;33(36):8982-8992. doi: 10.1021/acs.langmuir.7b02306. Epub 2017 Aug 21.
Recognizing the significance of surface interactions for ion rejection and membrane fouling in nanofiltration, we revise the theories of DLVO (named after Derjaguin, Landau, Verwey, and Overbeek) and non-DLVO forces in the context of polyamide active layers. Using an atomic force microscope, surface forces between polyamide active layers and a micrometer-large and smooth silica colloid were measured in electrolyte solutions of representative monovalent and divalent ions. While the analysis of DLVO forces, accounting for surface roughness, provides how surface charge of the active layer changes with electrolyte concentration, scrutiny of non-DLVO hydration forces gives molecular insight into the composition of the membrane-solution interface. Importantly, we report an expansion of the diffuse layer at high ionic strength, consistent with the recent development of the electrical double layer theory, but in contrast to the widely accepted phenomenon of aggregation in the secondary minimum. Further, the enhanced repulsion acting on modified membranes via polyelectrolyte adsorption can be quantitatively predicted by DLVO and non-DLVO forces. This work serves to solve past misunderstandings about the interaction forces acting on nanofiltration membranes, and it provides guidance for future work on the relation between surface properties and rejection mechanisms and fouling.
鉴于表面相互作用对纳滤中离子排斥和膜污染的重要性，我们在聚酰胺活性层的背景下修正了 DLVO（以德热纳、朗道、弗韦尔和奥弗贝克的名字命名）和非 DLVO 力理论。使用原子力显微镜，在具有代表性的单价和二价离子的电解质溶液中测量了聚酰胺活性层与微米级大而光滑的二氧化硅胶体之间的表面力。虽然考虑表面粗糙度的 DLVO 力分析提供了活性层表面电荷如何随电解质浓度变化，但对非 DLVO 水合力的仔细研究使我们能够深入了解膜-溶液界面的组成。重要的是，我们报告了在高离子强度下扩散层的扩展，这与最近电双层理论的发展一致，但与广泛接受的二级最小值聚集现象形成对比。此外，通过聚电解质吸附作用对改性膜施加的增强排斥力可以通过 DLVO 和非 DLVO 力进行定量预测。这项工作有助于解决过去对纳滤膜上作用的相互作用力的误解，并为未来关于表面特性与排斥机制和污染之间关系的工作提供指导。
