Selective Swelling of Polystyrene (PS)/Poly(dimethylsiloxane) (PDMS) Block Copolymers in Alkanes

Abstract

Block copolymers (BCPs) containing poly(dimethylsiloxane) (PDMS) blocks have been extensively used as precursors to prepare nanoporous materials with a diversity of compositions and morphologies. However, it remains desirable to facilely and efficiently transform the precursors into porous structures under mild conditions. Herein, we investigate the swelling behaviors of thin films of polystyrene-block-poly(dimethylsiloxane)-block-polystyrene (PS-b-PDMS-b-PS, SDS) in linear alkanes and produce well-defined nanoporosities in the SDS films following the mechanism of selective swelling-induced pore generation. Alkanes strongly swell PDMS blocks while slightly swell PS blocks, triggering the cavitation of the PDMS minority phases. The pore sizes as well as the porosities are determined by the interaction between the alkanes and the constituent blocks. Alkanes with lower carbon numbers exhibit a stronger affinity to the copolymer, leading to larger pores. Interestingly, we find that n-hexane is able to produce a porosity >30% at room temperature within a duration as short as 1 min. We demonstrate that PDMS, which has a lower surface energy, is enriched on the film surface, thus rendering a strong hydrophobicity to the produced porous SDS films. Ethanol permeation tests demonstrate the interconnected and accessible porosities and tunable flux as well as excellent pressure resistance of the porous SDS films, implying their potential applications as selective membranes in the filtration of organic solvents and oil/water separation.

Controlled Swelling of Monolithic Films as a Facile Approach to the Synthesis of UHMWPE Membranes

“…However, the proposed method could be very useful if, for some reason, it is difficult either to obtain a homogeneous mixture of the polymer and the solvent or to form it into the desired shape, which is the case for UHMWPE because of the very high viscosity of its solutions. In a way, the pore formation mechanism is very similar to the selective swelling-induced pore generation in block-copolymers [33][34][35][36][37][38]. In the case of UHMWPE homopolymer, the crystalline regions of the polymer act as impermeable blocks, while the solvent selectively swells the amorphous regions.…”

“…In a way, the pore formation mechanism is very similar to the selective swellinginduced pore generation in block-copolymers [33][34][35][36][37][38]. In the case of UHMWPE homopolymer, the crystalline regions of the polymer act as impermeable blocks, while the solvent selectively swells the amorphous regions.…”

“…The phenomenon of selective swelling of block-copolymers was implemented by Wang et al [33][34][35][36] and other researchers [37,38] to form a variety of porous structures. In the process of so-called selective swelling-induced pore generation, block-copolymer samples are immersed into a swelling agent with a high affinity to the minority block but almost inert to the majority block.…”

Core–Shell Double Gyroids Directed by Selective Solvation for ABC Triblock Terpolymers

“…This is attributed to the solvent‐dependent effective volume fraction deriving from the swelling or contraction of each block in the solvent. [ 30–44 ] For instance, Lo et al. [ 42 ] succeeded in fabricating six types of morphologies from a polystyrene‐ b ‐poly(dimethylsiloxane) by using multiple solvents.…”

“…This is attributed to the solvent-dependent effective volume fraction deriving from the swelling or contraction of each block in the solvent. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] For instance, Lo et al [42] succeeded in fabricating six types of morphologies from a polystyrene-b-poly(dimethylsiloxane) by using multiple solvents. The structural organization of the copolymer depended on the difference in solubility between the solvent and polystyrene and poly(dimethylsiloxane).…”