Solvent-Induced Swelling Behaviors of Microphase-Separated Polystyrene-block-Poly(ethylene oxide) Thin Films Investigated Using In Situ Spectroscopic Ellipsometry and Single-Molecule Fluorescence Microscopy

Abstract

Block copolymers have attracted considerable interest in the fields of nanoscience and nanotechnology because these polymers afford well-defined nanostructures via self-assembly. An in-depth understanding of solvent effects on the physicochemical properties of these microdomains is crucial for their preparation and utilization. Herein, we employed in situ spectroscopic ellipsometry and single-molecule fluorescence techniques to gain detailed insights into microdomain properties in polystyrene-block-poly­(ethylene oxide) (PS-b-PEO) films exposed to ethanol- and water-saturated N2. We observed a quick increase and a subsequent gradual decrease in the ellipsometric thickness of PS-b-PEO films upon exposure to ethanol-saturated N2. This observation was unexpected because ethanol-saturated N2 induced negligible thickness change for PS and PEO homopolymer films. The similarity in maximum thickness gain observed under ethanol- and water-saturated N2 implied the swelling of PEO microdomains. Ethanol vapor permeation through the PEO microdomains was supported by the redshift of the ensemble and single-molecule fluorescence emission of Nile red in PS-b-PEO films. Single-molecule tracking data showed the initial enhancement and subsequent reduction of the diffusion of hydrophilic sulforhodamine B molecules in PS-b-PEO films upon exposure to ethanol-saturated N2, consistent with the spectroscopic ellipsometry results. The higher ethanol susceptibility of the PEO microdomains was attributable to their amorphous nature, as shown by FTIR data.

Single-Molecule Fluorescence Investigations of Solute Transport Dynamics in Nanostructured Membrane Separation Materials

“…52−54 We also studied the effects of the deswelling of thin PS-b-PEO films on the width and permeability of cylindrical PEO microdomains using SMT. 55 In the most recent study, 51 we monitored the thickness and solute permeability of PS-b-PEO films under ethanol or water vapor using spectroscopic ellipsometry and single-molecule fluores-cence techniques. Ethanol is a poor solvent for both PS and PEO homopolymers.…”

“…We assessed the solvent-induced swelling behavior of PEO microdomains in polystyrene- block -poly­(ethylene oxide) (PS- b -PEO, Figure a) films using single-molecule fluorescence techniques . We previously investigated the morphology of PEO microdomains in PS- b -PEO films from the diffusion trajectories of single SRB molecules, which selectively partition to PEO microdomains (Figure a). − We also studied the effects of the deswelling of thin PS- b -PEO films on the width and permeability of cylindrical PEO microdomains using SMT .…”

“…We previously investigated the morphology of PEO microdomains in PS- b -PEO films from the diffusion trajectories of single SRB molecules, which selectively partition to PEO microdomains (Figure a). − We also studied the effects of the deswelling of thin PS- b -PEO films on the width and permeability of cylindrical PEO microdomains using SMT . In the most recent study, we monitored the thickness and solute permeability of PS- b -PEO films under ethanol or water vapor using spectroscopic ellipsometry and single-molecule fluorescence techniques. Ethanol is a poor solvent for both PS and PEO homopolymers.…”

“…(c) SMT trajectory data obtained for a PS- b -PEO film under N 2 (left) and after exposure to ethanol-saturated N 2 for 2 min (middle) and 12 min (right). Adapted with permission from ref . Copyright 2022 American Chemical Society.…”