Ordered isoporous membranes from ionic diblock copolymers via SNIPS: Optimizing effective factors with a structural survey

How does Micro‐ and Macro‐Phase Separation of Block Copolymers Affect the Formation of Integral Asymmetric Isoporous Membranes? A Review on Effective Factors

“…[54] At the air-solution interface of the solution-cast film, which is considered as the concentrated regime, micelles with crew-cut structure favor the 2D honeycomb-hexagonal lattice formation (2DH, 3 m point group symmetry for the micelles). [23,45,46,49,71,72] However, star-like micelles pack on the usual triangularhexagonal lattice (6 mm point group symmetry for the micelles), also named as hexagonally ordered 1D cylinders or hexagonally packed cylinders (HEX). [45,73,74] Therefore, in the 2DH lattice geometry, the "missing" micelles in the middle of hexagons are considered as the origin of the membrane pores, [75][76][77][78] whereas, in the triangular-hexagonal lattice, the minority hydrophilic block would give rise to the pores after drying membrane.…”

“…In the case of reverse micelles, they order into the hexagonal close-packed (HCP) spheres geometry, then lattice geometry is practically immobilized without structural inversion by immersion in a low-temperature non-solvent bath. [54,71] Hence, coronas (i.e., hydrophobic majority-block) of adjacent micelles on the film surface fuse together to form the membrane matrix, while "pores" (i.e., nanoscale voids) are formed between the densely packed micelles. [71,79] Consequently, the porewall at the membrane selective-layer is made of the hydrophobic majority-block (Figure 2c).…”

“…[54,71] Hence, coronas (i.e., hydrophobic majority-block) of adjacent micelles on the film surface fuse together to form the membrane matrix, while "pores" (i.e., nanoscale voids) are formed between the densely packed micelles. [71,79] Consequently, the porewall at the membrane selective-layer is made of the hydrophobic majority-block (Figure 2c).…”

“…However, the calculated/reported values for the interaction parameters (𝜒 AB ) concerning various PS-based BCPs, which are mostly used in the SNIPS process so far, are almost low (Table 2). [71,106,107] Low 𝜒 AB BCPs, for example, PS-b-PNIPAM and PS-b-PEO, have shown obviously inferior pore formation capability in addition to inappropriate pore uniformity/homogeneity, due to their weakly segregated characteristic (Figure 5). [52,106,114] PS-b-P4VP membranes.…”

“…[45,[50][51][52]70,103] In this context, SNIPS membranes with suitable isoporous structures were prepared from relatively high 𝜒 AB PS-b-PAA copolymers that had the MW of about 70 kDa (without the aid of foreign additives or increasing the BCP casting solution concentration). [54,71] Accordingly, the successful fabrication of isoporous membranes through SNIPS is mainly dependent on using BCPs with larger N or higher 𝜒 AB .…”