Self-Assembly of a Midblock-Sulfonated Pentablock Copolymer in Mixed Organic Solvents: A Combined SAXS and SANS Analysis

Abstract

Ionic, and specifically sulfonated, block copolymers are continually gaining interest in the soft materials community due to their unique suitability in various ionexchange applications such as fuel cells, organic photovoltaics, and desalination membranes. One unresolved challenge inherent to these materials is solvent templating, that is, the translation of self-assembled solution structures into nonequilibrium solid film morphologies. Recently, the use of mixed polar/nonpolar organic solvents has been examined in an effort to elucidate and control the solution self-assembly of sulfonated block copolymers. The current study sheds new light on micellar assemblies (i.e., those with the sulfonated blocks comprising the micellar core) of a midblock-sulfonated pentablock copolymer in polar/nonpolar solvent mixtures by combining small-angle X-ray and small-angle neutron scattering. Our scattering data reveal that micelle size depends strongly on overall solvent composition: micelle cores and coronae grow as the fraction of nonpolar solvent is increased. Universal model fits further indicate that an unexpectedly high fraction of the micelle cores is occupied by polar solvent (60−80 vol %) and that partitioning of the polar solvent into micelle cores becomes more pronounced as its overall quantity decreases. This solvent presence in the micelle cores explains the simultaneous core/ corona growth, which is otherwise counterintuitive. Our findings provide a potential pathway for the formation of solventtemplated films with more interconnected morphologies due to the greatly solvated micellar cores in solution, thereby enhancing the molecular, ion, and electron-transport properties of the resultant films.

Global fitting of multiple data frames from SEC–SAXS to investigate the structure of next-generation nanodiscs

“…This has been widely exploited and several examples are available in the literature for various types of systems, i.e. microemulsions (Arleth & Pedersen, 2001), nanodiscs (Skar-Gislinge et al, 2010), the self-assembly of polymers into toroids (Hollamby et al, 2016) and micelles (Mineart et al, 2019), and in the case of specifically deuterated proteins in solution (Whitten et al, 2007;Heller et al, 2003).…”

Effects of Trace Water on Self-Assembly of Sulfonated Block Copolymers During Solution Processing

“…In one of these examples, the SPC was dried before dissolving in the solvent, 21 but the other study did not specify the water content. 22 As polymer loading in the solvent is increased, the SPC can assemble into either ordered or disordered morphologies, depending on the solvent composition. For example, when the SPC is dissolved in nP/ T solvent mixtures at a loading of 20 wt %, which includes 20 wt % water from storage at ambient humidity, the structure after 2 days of dissolution at room temperature is lamellar (LAM) for 29−36 wt % nP and disordered (DIS) for 40−50 wt % nP.…”

“…In this work, we studied the effects of trace water on self-assembly of a sulfonated pentablock copolymer (SPC), poly­( tert -butylstyrene- b -hydrogenated isoprene- b -sulfonated styrene- b -hydrogenated isoprene- b - tert -butylstyrene) (tBS-HI-SS-HI-tBS). The solution-state self-assembly of this SPC has been studied in prior works, and depending on the polymer concentration and solvent polarity, the SPC can either dissolve into free chains or assemble into spheres, lamellae, and disordered nanoscale aggregates. ,− The structures of solution-cast SPC films have also been studied, and morphologies such as lamellae, cylinders, and spheres have been observed depending on the solvent type used for casting. ,− Trace water is difficult to avoid during the solution processing of SPC into films as the material soaks up water when stored at ambient humidity due to the hygroscopic sulfonated midblock. , As a result, the solution will contain small amounts of water (ca. 1–5 wt %) unless the polymer is dried prior to dissolution or the solution is dried prior to use.…”

Interfacial Response and Structural Adaptation of Structured Polyelectrolyte Thin Films

“…It is distinguished in its nanostructured interface that differs from that formed by lower dimension copolymers. The intriguing structure and potential technological uses of this copolymer have driven numerous studies of solutions − and membranes, − with immense efforts to correlate macroscopic transport and structure. , These studies, however, have provided macroscopic correlations where direct molecular insight into the factors that govern transport remains a missing link. Of particular significance is the interfacial dynamics that facilitate transport in these highly structured ionizable copolymers, including those that occur at the membrane’s interfaces and within internal boundaries.…”