Influences of support layer deformation on the intrinsic resistance of thin film composite membranes

Published: September 13, 2018

Author(s)

Masoud Aghajani, Mengyuan Wang, Lewis M. Cox, Jason P. Killgore, Alan R. Greenberg, Yifu Ding

Abstract

It is commonly believed that the overall resistance of thin film composite (TFC) membranes is dictated by the crosslinked, ultrathin polyamide barrier layer, while the porous supports merely serve as the mechanical support. Although this scenario might be true under low transmembrane pressure, it becomes questionable under high transmembrane pressure. A highly porous support normally yields under a few MPa pressure, which can result in a significant level of compressive strain, and significantly increase the resistance to permeation. However, the influence of deformation of the porous support on the overall resistance of the TFC membrane remains unclear. Particularly, it is challenging to determine the strain/deformation of the membrane during active separation processes. In this study, we use nanoimprint lithography to achieve precise compressive deformation in commercial TFC membranes. By adjusting the nanoimprint lithography (NIL) conditions, membranes were compressed to strain level up to 60 %. SEM and AFM measurements showed that the compression had minimum impact on the barrier layer surface morphology and total surface area, and most deformation occurred in the support layers. DI water permeation measurements revealed that degree of compaction decreases with an increase of strain level. Most significantly, the intrinsic membrane resistance showed negligible changes at strain levels lower than 30 % - 40 %, but increased exponentially at higher strain level, reaching 255 %, 390 %, and 490 % of the values of pristine membranes for strains of x, y, and z. Using a resistance-in-series model, the strain- dependency of the TFC membrane resistance can be qualitatively described.
Citation: Journal of Membrane Science
Volume: 567
Pub Type: Journals
Created September 13, 2018, Updated November 10, 2018