(437e) Expanding Membrane Functionality through Additive Manufacturing

Expanding
Membrane Functionality Through Additive Manufacturing

William
A. Phillip, John R. Hoffman, Feng Gao

Department
of Chemical & Biomolecular Engineering

University
of Notre Dame

Abstract:

As interest
in decentralized water treatment technologies grows, the development of
nanofiltration (NF) as a complementary process to reverse osmosis has emerged. However,
NF membranes that overcome the tradeoff between selectivity and permeability, that
expand the range of molecules that can be selectively separated, and that
resist the detrimental effects of fouling must be developed in order to realize
the potential of NF-based processes. One approach for overcoming the
permeability-selectivity trade-off is through the development of membranes with
better controlled pore sizes and pore size distributions. In fact, the
performance of NF membranes based on self-assembled materials is already pushing
the limits of these size-selective separation mechanisms. Therefore, many
researchers are considering approaches that move beyond improved control of size-selective
separation mechanisms. In this regard, the functionality lining the pore walls
of NF membranes offers another means through which to increase selectivity
without sacrificing permeability. Specifically, due to the small pore size of
NF membranes, electrostatic interactions and van der Waals forces affect solute
permeation dramatically. This feature presents several opportunities for the
introduction of functionalities that enable molecular separations based on
chemical factors. In regards to
fouling, a multitude of antifouling chemistries have been identified, yet introducing these functional
chemistries without disrupting the nanostructure of the membranes and in a
manner that is consistent with state-of-the-art membrane manufacturing
processes remains a challenge.

In this
talk, we will discuss how inkjet printing and click chemistry can be used to functionalize
membrane chemistries in a precise manner and on time scales consistent with
roll-to-roll manufacturing. Specifically, the copper-catalyzed azide-alkyne cycloaddition (CuAAC)
reaction mechanism is examined. Using an inkjet printer, reactive ink solutions
containing an alkyne-terminated molecule are deposited on nanostructured copolymer
membranes with azide-functionalized surfaces. Using
Fourier Transform Infrared spectroscopy, the progress of the reaction was
quantified by monitoring the decreasing intensity of the peak associated with
the azide groups. We will discuss how the rate of
membrane functionalization could be controlled through the formulation of the
reactive ink solutions as well as the inkjet printing process. In the limit of
a rapid CuAAC reaction, full functionalization (i.e.,
azide conversion) could be accomplished in under 60
seconds. Moreover, a model that predicts the percent conversion of the azide moieties as a function of the reactive solution
formulation and processing time was developed and validated. These findings
offer a controlled functionalization protocol that is compatible with
roll-to-roll processing rates. As such, we provide examples of how this
protocol 1) enables the chemical-patterning of membranes in order to access
emergent transport mechanisms, and 2) generates multifunctional membranes
capable of resisting the detrimental effects of fouling while exhibiting highly
selective separations. Through
these examples, we will demonstrate that membranes
that are functionalized post-assembly using additive manufacturing approaches provide
a scalable platform that can be tailored to myriad separations for the treatment and conservation of water resources.