Structure and transport properties of self-assembled nanofiltration membranes based on sustainably derived materials

Abstract

The development of functional polymers using sustainable resources is an increasingly important pursuit. Unsaturated fatty acids represent a potentially interesting class of renewable materials for this purpose. Their unsaturated carbon bonds permit crosslinking to form solid polymers. Additionally, their carboxylic acid functional groups provide for the display of specific surface chemistry within the resulting polymers, and also enable chemical derivatization. Here, we explore the fabrication of nanometer-scale size-selective membranes using conjugated linoleic acid derived monomers. Potassium salt conjugated linoleic acid surfactants (KCLA) self-assembled to form hexagonally packed cylinders (HI) in an aqueous medium containing glycerol. This structure provides a highly ordered medium with aqueous-continuous channels for nanofiltration. The HI mesophase was crosslinked with the addition of bifunctional comonomers and the ordered structure was retained with good fidelity in the resulting thin polymer films (< 400 nm thick). These film function effectively as nanofiltration membranes, with a size cut-off of approximately 1.2 nm for charged solutes, while maintaining a high permeance of ∼ 9 LMH/bar. This performance is on par with several commercial nanofiltration membranes and these materials are therefore of potential interest for advancing sustainability concerns in practical nanofiltration applications.