Molecular tailoring of polystyrene-block-poly (acrylic acid) block copolymer toward additive-free asymmetric isoporous membranes via SNIPS

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

“…[49,[68][69][70] Moreover, reverse micelles of BCPs could either act similar to the soft or hard spheres (depending on the length of hydrophobic majority-block), and therefore the BCC or FCC lattice geometries would be formed, respectively. [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).…”

“…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).…”

“…In this context, the differences in the solubility of each block and solvent(s), that is, (𝛿 block − 𝛿 solvent ) 2 , or more precisely, the solvent-polymer (or BCP) interaction parameter (𝜒 12 ), [80][81][82] is frequently used in the literature to evaluate which block is preferentially exposed to the solvent(s). [52,54,79,[83][84][85] The (𝛿 block − 𝛿 solvent ) 2 and 𝜒 12 give almost a good indication of the interaction strength between the blocks and the solvent(s). In this way, smaller values indicate stronger interactions and therefore, that block will tend to have contact with the solvent(s).…”

“…[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 .…”

“…For instance, amphiphilic BCPs with higher MWs lead to enlargement of the pore diameters with a linear trend, [13,70,92,115] because higher MW BCPs form larger micellar assemblies in solution. [54] Moreover, diblock copolymers with higher MWs, generally result in non-uniform pore sizes at the membrane surface, [115] that will affect their performance in molecular separation applications. [116] The formation of mostly "pits" instead of open pores in addition to lower surface-pore densities have been also reported for the relatively high MW copolymers used in membrane formation via SNIPS.…”