Combined Experimental and Theoretical Study of Weak Polyelectrolyte Brushes in Salt Mixtures

Joshua D. Willott* (Corresponding Author), Ben A. Humphreys, Grant B. Webber, Erica J. Wanless, Wiebe M. De Vos

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

3 Citations (Scopus)
37 Downloads (Pure)

Abstract

The swelling behavior of a hydrophobic poly(2diisopropylamino)ethyl methacrylate (PDPA) brush immersed in aqueous solutions of single and mixed salts has been investigated using ellipsometry and numerical self-consistent field (nSCF) theory. As a function of solution ionic strength, the osmotic and salted brush regimes of weak polyelectrolyte brushes as well as substantial specific anion effects in the presence of K + salts of Cl - , NO 3 - , and SCN - are found. For solutions containing mixtures of NO 3 - and Cl - , the brush swelling is the same as one would expect on the basis of the concentration-weighted average of the brush behavior in the single salt solutions. However, in mixtures of SCN - and Cl - , the swelling response is more complicated and substantial divergence from ideal behavior is observed. Mean-field theory shows excellent qualitative agreement with the ellipsometry findings. nSCF reveals that for the SCN - /Cl - cases the swelling behavior of the PDPA brush most likely arises from the predominant localization of the weakly hydrated SCN - within the brush compared to the more strongly hydrated Cl - .

Original languageEnglish
Pages (from-to)2709-2718
Number of pages10
JournalLangmuir
Volume35
Issue number7
DOIs
Publication statusPublished - 19 Feb 2019

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