Block Polymer Solution Assembly For Nanoporous Membrane Fabrication

Jessica L Sargent, Purdue University

Abstract

The field of separation technology is rapidly advancing, and many of these advances have depended upon block polymers. Block polymers’ unique ability to selfassemble into ordered nanostructures possessing regions with distinct chemistries has made these materials particularly valuable in nanofiltration and reverse osmosis applications. In this thesis, we detail recent advances in state-of-the-art membranes using block polymers and continue to build upon these advances using the triblock polymer polyisoprene-b-polystyrene-b-poly( N,N-dimethylacrylamide) (PI-PS-PDMA). This polymer is cast into thin film nanoporous membranes by the self-assembly and nonsolventinduced phase separation (SNIPS) process. Synthesis of these polymers and subsequent fabrication of membrane materials has been widely studied. However, the early selfassembly of PI-PS-PDMA in solution is still poorly understood, despite characterization of this solution behavior being critical for application of these materials to commercial processes. The early self-assembly of triblock polymers in solution can be investigated through a combination of dynamic light scattering, small-angle x-ray scattering, and atomic force microscopy. Elucidation of this solution behavior provides for the development of relationships between polymer solution properties and polymer assembly prior to SNIPS membrane fabrication. These guiding relationships can then be employed to interrogate the solution behavior of block polymers for membrane fabrication and optimize the casting solutions and membrane microstructure for SNIPS-cast membranes. A particular benefit of the PI-PS-PDMA triblock polymer is the facile conversion of the pore-forming polymer block to a chemical functionality of interest for specific separations. This property makes this A-B-C block polymer system of great value for advances in nanofiltration and reverse osmosis membranes. However, the PI-PS-PDMA system has thus far been incapable of forming membranes possessing pore sizes small enough for use in reverse osmosis. As such, alternative C-block chemistries are being investigated. The C-block poly(tert -butyl methacrylate) (PtBMA) is of particular interest due to the ease with which one can apply protocols developed for PI-PS-PDMA to the PIPS- PtBMA system. PtBMA can be synthesized and chemically modified similarly to its PDMA predecessor, and it has been proven to form smaller pores. With additional efforts to improve the microstructure of PI-PS-PtBMA membranes, this system could prove capable of producing sub-nanometer pores for reverse osmosis separations.

Degree

M.S.Ch.E.

Advisors

Boudouris, Purdue University.

Subject Area

Polymer chemistry|Chemical engineering|Materials science

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