TRIBLOCK TERPOLYMER DERIVED ISOPOROUS ULTRAFILTRATION MEMBRANES
Li, Yuk Mun
Block copolymer derived nanostructured materials provide a unique platform for the development of nanotechnological applications ranging from the microelectronics industry all the way to separation. A particularly interesting approach that has received increasing attention in the last couple of years is the formation of isoporous ultrafiltration membranes via the combination of block copolymer self-assembly (SA) with industrially proven non-solvent induced phase separation (NIPS), a process now referred to as SNIPS. Triblock terpolymer based NIPS membranes have been investigated as a result of their improved mechanical toughness over the corresponding diblock copolymer derived membranes. To expand our understanding of this new area of block copolymer science and engineering, in this thesis SNIPS derived membranes were investigated based on triblock terpolymer poly(isoprene-b-styrene-b-4-vinylpyridine) (ISV). In a first effort, the effects of different casting parameters on membrane substructure morphology were studied. Experimental results elucidated a substructure morphology transition from finger-like to sponge-like through increasing dope concentration, evaporation time, and varying solvent compositions. Membranes with finger-like and sponge-like substructures were integrated with nylon supports to enhance mechanical stability for testing and handling and were evaluated for their hydraulic permeabilities. The effects of an important but often overlooked environmental casting parameter, relative humidity, were subsequently assessed on ISV membranes with a focus on membrane surface pore structure. Membranes cast at an optimized relative humidity of 40% were characterized by a high density of square packed surface pores. Additionally, precise control over the rate of permeation of a small molar mass solute was realized through variation in triblock terpolymer molar mass. After investigation of the SNIPS process and the associated molecular engineering of membrane properties via variation of process parameters and molecular architecture, new insights into the fabrication of asymmetric membranes were obtained from employing two chemically distinct triblock terpolymers in the dope used during the SNIPS process. Initial proof-of-principle experiments with mixtures of ISV and poly(isoprene-b-styrene-b-(dimethylamino)ethylmethacrylate) (ISA) demonstrated that the use of mixtures of chemically distinct triblock terpolymers enables the tailoring of membrane pore surface chemistries. This approach was subsequently used to improve membrane fouling properties by working with mixtures from ISV and terpolymer poly(isoprene-b-styrene-b-ethylene oxide) (ISO) which on its own is difficult to process into useful SNIPS membranes. Experimental results established that blended triblock terpolymer membranes exhibited a combination of properties intrinsic to the two specific block copolymers utilized. This opens access to designer membranes with desired pore surface chemical properties via a facile “mix and match” approach. The results of this thesis taken together highlight the tremendous potential of SNIPS derived membranes to become the basis for next generation ultrafiltration technologies for applications in areas as diverse as biopharmaceutical separations, virus filtration, and drug delivery.
Chemical engineering; asymmetric; block copolymer; membranes; ultrafiltration; SNIPS; Materials Science; Self-assembly
Wiesner, Ulrich B.
Joo, Yong L.; Estroff, Lara A.
Ph. D., Chemical Engineering
Doctor of Philosophy
Attribution 4.0 International
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution 4.0 International