(716d) Salt Permeation Mechanisms through Inkjet Printed Charge Mosaic Membranes

Salt Permeation Mechanisms Through Inkjet Printed

Charge Mosaic Membranes

Mark J. Summe, Sushree Jagriti Sahoo, William A.
Phillip*

Department of Chemical and Biomolecular Engineering,
University of Notre Dame,

205 McCourtney Hall, Notre
Dame, IN 46556, USA. E-mail:
wphillip@nd.edu

Abstract

Charge
mosaic membranes are
capable of transporting dissolved salts more rapidly than neutral molecules of
comparable size. The ability of these thin polymeric films to facilitate the
transport of the charged species is due to their unique microstructure, which consists of distinct
positively-charged and negatively-charged domains that traverse the membrane
thickness. Recently, we developed a method
for producing charge mosaic membranes in a scalable manner by inkjet printing composite
polymeric inks onto a structural template. Namely, mosaic patterns consisting of
positively-charged, poly(diallyldimethylammonium
chloride) and negatively-charged, poly(sodium 4-styrene sulfonate) domains were
printed on polycarbonate track-etched (PCTE) membranes using a commercial
inkjet printer. When tested in pressure-driven piezodialysis
experiments, the charge
mosaic membranes fabricated using this robust, reliable, and rapid method were
able to enrich the
concentration of potassium
chloride in the permeate solution relative to the feed solution.

In order to guide the design and optimization
of these charge mosaic membranes, a fundamental understanding of the salt
permeation mechanisms through them is still needed. In this regard, inkjet
printing is an attractive method for fabricating charge patterned membranes
because it allows for facile control over the patterned membrane
microstructure. This microstructure, in turn affects membrane performance. As
such, in this study, we utilize inkjet printing to produce charge patterned
membranes of varied composition (i.e., positively-charged, mosaic patterned,
and negatively-charged) and quantify the salt permeability of the three
membranes in diffusion cell experiments. The permeabilities
of the membranes are characterized as a function of salt identity; potassium
chloride (KCl), magnesium chloride (MgCl₂),
potassium sulfate (Na₂SO₄), and magnesium sulfate (MgSO₄)
are selected as solutes because they comprise of ions that cover a representative
range of valence numbers. Additionally, the permeabilities
of the membranes are quantified as a function of feed solution concentration. A
simple theoretical framework capable of describing the trends in salt permeability
through the charged membranes as a function of salt identity and concentration
is detailed. Inkjet printing offers a straightforward and scalable route toward
the design and fabrication of charge mosaic membranes that could find use in
the myriad applications that rely on the rapid transport of charge solutes. Moreover,
it enables the generation of fundamental insights regarding the mechanisms
governing transport through charge-patterned membranes.