Inkjet Printed Chemically-Patterned Polymeric Nanomaterials for Aqueous Membrane Separations

While the clear majority of membrane separations processes are dominated by size-selectivity, the field of chemically-functionalized membranes is rapidly expanding. These membranes offer control of mass transfer by manipulating its nanostructure. Still, these processes largely involve the permeation of the majority of solution across the membrane layer. There are several separation processes for which this is highly inefficient, particularly dilute systems, like sensors and wastewater reuse. It would be more energetically favorable to transport only the large, dilute contaminants, while leaving behind the small solvent molecules. This can be made possible by tuning the surface chemistries of the membrane, which is, in turn, made possible by the field of surface patterning.

Template assisted ink-jet printing of polymeric materials is an effective method of patterning permeable surfaces to design different nanostructures (i.e., nanotubes, nanowires, thin films) by simply varying printing conditions. Furthermore, printing enables the patterning of different, opposing chemistries onto a single support, which can engender different transport phenomena that either individual component. The focus of this study was charge-patterned mosaic membranes, which contain bicontinuous, discrete domains of opposite charge. This unique morphology facilitates the transport of charged species through oppositely charged domains, leading to an enrichment (i.e., increased) concentration of salt in the permeate.

Due to past difficulty in producing charge-patterned mosaic membranes with well-defined nanostructures, development in this area has lagged, leading to a void in the understanding of the fundamental transport mechanisms. Inkjet printing of nanomaterials, however, allowed for a facile, rapid, and reliable fabrication method to engender fine control over the microstructure, which subsequently affects membrane performance.

This dissertation details a rigorous theoretical model to explain this unusual transport behavior and validated it with experimental observations made possible by the unique ability to produce both single-charged and charge-patterned membranes from the same chemistries. We showed that patterning the surface with multiple components produces an altogether different transport profile in the charge-patterned structure that is unlike either of its components.