Asymmetric Membranes from Two Chemically Distinct Triblock Terpolymers Blended during Standard Membrane Fabrication

Abstract

Deviating from the traditional formation of block copolymer derived isoporous membranes from one block copolymer chemistry, here asymmetric membranes with isoporous surface structure are derived from two chemically distinct block copolymers blended during standard membrane fabrication. As a first proof of principle, the fabrication of asymmetric membranes is reported, which are blended from two chemically distinct triblock terpolymers, poly(isoprene-b-styrene-b-(4-vinyl)pyridine) (ISV) and poly(isoprene-b-styrene-b-(dimethylamino)ethyl methacrylate) (ISA), differing in the pH-responsive hydrophilic segment. Using block copolymer self-assembly and nonsolvent induced phase separation process, pure and blended membranes are prepared by varying weight ratios of ISV to ISA. Pure and blended membranes exhibit a thin, selective layer of pores above a macroporous substructure. Observed permeabilities at varying pH values of blended membranes depend on relative triblock terpolymer composition. These results open a new direction for membrane fabrication through the use of mixtures of chemically distinct block copolymers enabling the tailoring of membrane surface chemistries and functionalities.

Structural Evolution of Ternary Amphiphilic Block Copolymer Solvent Systems for Phase Inversion Membrane Formation

“…This remains the case even after extensive studies based on considerations of solubility parameters, small-angle neutron scattering (SANS) experiments, as well as cryo-electron microscopy (cryo-EM), atomic force microscopy (AFM), and dynamic light scattering investigations . A more comprehensive understanding of the micellar structure as a function of solvent composition will be crucial in the design of more advanced SNIPS membranes, e.g ., for the control of the spatial distribution of constituent BCPs in blended membranes based on the immiscibility between different species of micelles, micelle–solvent interactions, and surface energies of micelles …”

“…15 A more comprehensive understanding of the micellar structure as a function of solvent composition will be crucial in the design of more advanced SNIPS membranes, e.g., for the control of the spatial distribution of constituent BCPs in blended membranes based on the immiscibility between different species of micelles, micelle−solvent interactions, and surface energies of micelles. 23 Herein, we propose such a comprehensive analysis of the solvent composition-driven structural evolution of the ISV/ DOX/THF system by converging results from solution SAXS, in situ GISAXS, the study of polymer chain dynamics based on spin−spin relaxation time (T 2 ) analysis using solution 1 H NMR spectroscopy, and scanning electron microscopy (SEM) observations of the final membrane top surface. First, we will develop a ternary phase diagram for ISV/DOX/THF based on solution SAXS.…”

Non-Equilibrium Block Copolymer Self-Assembly Based Porous Membrane Formation Processes Employing Multicomponent Systems

“…If, in a blended polymer dope, the homopolymer component described above is replaced by a second BCP, preferably one that has a different pore-forming (micelle core forming) block, then co-assembly of the two micelle populations should result in a separation layer with two different pore chemistries (see schematic depiction in Figure 15m), provided that (1) both populations preferentially adsorb the same solvent and (2) do not undergo chain exchange on the SNIPS timescale (<100 s). For the first time, Li et al successfully demonstrated this concept using ISV and poly(isoprene-b-styrene-b-dimethylaminoethyl methacrylate) (PI-b-PS-b-PDMAEMA, ISA), two terpolymers that differ only in their pore-forming blocks [86]. The chemically identical corona blocks (PI + PS) ensure that the above-mentioned solvent-driven surface segregation effects do not apply, while the room-temperature processing conditions, relatively large molar masses (~100 kg/mol), and relatively concentrated BCP casting solutions (15 wt.…”

Fit-for-purpose block polymer membranes molecularly engineered for water treatment

“…Another iteration of this approach, which was discussed above, used the blending of chemically distinct block polymers (i.e., A-B and A-C types) to provide the desired functionality. [109][110][111][112] While the minimal processing needed after membrane fabrication for this approach is attractive, the flexibility of the functional groups that can be used as the poreforming block may be slightly limited by the requirement that the material self-assemble during membrane fabrication.…”