Underscreening in concentrated electrolytes: re-entrant swelling in polyelectrolyte brushes
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Date
2023-09-30
Journal Title
Journal ISSN
Volume Title
Publisher
Royal Society of Chemistry
Abstract
Hypersaline environments are ubiquitous in nature and are found in myriad technological processes. Recent empirical studies have revealed a significant discrepancy between predicted and observed screening lengths at high salt concentrations, a phenomenon referred to as underscreening. Herein we investigate underscreening using a cationic polyelectrolyte brush as an exemplar. Poly(2-(methacryloyloxy)ethyl)trimethylammonium (PMETAC) brushes were synthesised and their internal structural changes and swelling response was monitored with neutron reflectometry and spectroscopic ellipsometry. Both techniques revealed a monotonic brush collapse as the concentration of symmetric monovalent electrolyte increased. However, a non-monotonic change in brush thickness was observed in all multivalent electrolytes at higher concentrations, known as re-entrant swelling; indicative of underscreening. For all electrolytes, numerical self-consistent field theory predictions align with experimental studies in the low-to-moderate salt concentration regions. Analysis suggests that the classical theory of electrolytes is insufficient to describe the screening lengths observed at high salt concentrations and that the re-entrant polyelectrolyte brush swelling seen herein is consistent with the so-called regular underscreening phenomenon. © the Owner Societies 2023 This article is Open Access - CC-BY-NC
Description
Keywords
Electrolytes, Swelling, Salts, Synthesis, Neutron reflectors, Spectroscopic factors, Screening, Concentration ratio, Colloids, Debye Length
Citation
Robertson, H., Elliott, G. R., Nelson, A. R. J., Le Brun, A. P., Webber, G. B., Prescott, S. W., Craig, V. S. J., Wanless, E. J., & Willott, J. D. (2023). Underscreening in concentrated electrolytes: re-entrant swelling in polyelectrolyte brushes. Physical Chemistry Chemical Physics, 25(36), 24770-24782. doi:10.1039/D3CP02206D