Applications Of Supramolecular Interaction On Isoporous Membrane Fabrication:Process And Mechanism Investigations

Membrane separation is a novel,state-of-the-art separation technology for its high efficiency and low energy consumption.However,it is always difficult to achieve a balance between permeability and selectivity,which is well-known as the trade-off effect.Increasing porosity and reducing pore size distribution are important ways to overcome this effect.Therefore,the research on isoporous membranes becomes critically important.Isoporous membranes based on block copolymers(BCPs)represent a new generation of separation membranes,and the method to prepare isoporous membranes using a combination of self-assembly and non-solvent induced phase separation(SNIPS)has received considerable attention for its compatibility with scalable preparation.However,there are still many problems need to be solved which are related to the characteristics of BCPs.For instance,it is difficult to prepare isoporous membranes with pore size smaller than 10 nm from the SNIPS strategy;The continuous change of isoporous structure during the solvent evaporation has laid down great difficulties for the practical preparation,and some special BCPs with unique functions that are desirable for separations can be hardly fabricated into isoporous membranes because of the low phase separation tendency.These listed instances are representative problems preventing isoporous membranes from real applications.It has been reported that the supramolecular interactions between additives and BCPs can effectively regulate the BCPs self-assemble,which is critical to the formation of isoporous membranes.Based on these findings,this thesis adopted three additives with specific structures/functions to tailor the self-assembly of BCPs.Chapter 3 used polystyrene-block-poly(4-vinylpyridine)(PS-b-P4VP)with a molecular weight of 5.9kg/mol as the membrane-forming material and the sulfonated polyethylene glycol(SPEG)as the additive.Due to the selective ionic interaction between the SPEG and P4VP,the assembly of BCPs was promoted and isoporous membrane with a pore size of about 7.3nm was successfully prepared.As-fabricated membranes were found to effectively separate protein pairs with similar size.Chapter 4 used the organic acids to stabilize the phase-separated structure of the BCPs in solution.Therefore,the time window that retains isoporous structure was extended to more than 200 s,which is important for the defect control and reproductive preparation in scale fabrication.In Chapter 5,polyacrylic acid was used as the additive to promote the phase separation of polystyrene-block-poly(N-isopropylacrylamide)(PS-b-PNIPAM)which is difficult to form isoporous membranes because of its low Flory interaction parameter(?).Small-angle X-ray Scattering(SAXS),nuclear magnetic resonance(~1H-NMR),and Fourier transform infrared spectrometer(FT-IR)were used to inspect the interaction between additives and block polymers in casting solutions.Surface morphologies of prepared membranes were analyzed by field emission scanning electron microscopy(FE-SEM).This thesis has studied the ionic interaction,hydrogen bonding,and homopolymer additive on regulating the self-assembly of BCPs during membrane formation.It was found that the additives had played an important role on promoting and stabilizing the microphase separation of block copolymers in membrane formation.The non-covalent binding and supramolecular interaction between the additive and the block copolymer link the additive to the block polymer to form a new"supramolecular block copolymer",which is interpreted as the reason for the strengthened phase separation and stabilized microstructure for the BCPs dissolved in solution.These findings are important to the controllable fabrication and performance improvement for isoporous membranes produced from BCPs via the SNIPS strategy.