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The entropy of water in swelling PGA/PAH polyelectrolyte multilayers


Zahn, Raphael; Bickel, Katrin R; Zambelli, Tomaso; Reichenbach, Judith; Kuhn, Frank M; Vörös, János; Schuster, Rolf (2014). The entropy of water in swelling PGA/PAH polyelectrolyte multilayers. Soft Matter, 10(5):688-693.

Abstract

We investigated the thermodynamical properties of water exchanged in poly(L-glutamic acid)/poly(allylamine)hydrochloride (PGA/PAH) polyelectrolyte multilayers containing ferrocyanide. Oxidation/reduction of the ferrocyanide in the multilayer caused a reversible swelling/contraction of the film due to the uptake/release of counter ions and water. We used electrochemical quartz crystal microbalance and electrochemical microcalorimetry to correlate the amount of water with the accompanying entropy changes during electrochemical swelling of the multilayer for a series of different anions at different concentrations. The number of exchanged water molecules was highly dependent on the ionic strength and the type of anion in the buffer solution. However, the entropy change per exchanged water molecule was found to be independent of these two parameters. The water molecules in the polyelectrolyte multilayer have reduced the entropy compared to that of bulk water (≈−1 J mol−1 K−1). A comparison of hydration entropies for free polyelectrolytes and PGA/PAH multilayers suggests that such systems are mainly stabilized by water release during multilayer construction.

Abstract

We investigated the thermodynamical properties of water exchanged in poly(L-glutamic acid)/poly(allylamine)hydrochloride (PGA/PAH) polyelectrolyte multilayers containing ferrocyanide. Oxidation/reduction of the ferrocyanide in the multilayer caused a reversible swelling/contraction of the film due to the uptake/release of counter ions and water. We used electrochemical quartz crystal microbalance and electrochemical microcalorimetry to correlate the amount of water with the accompanying entropy changes during electrochemical swelling of the multilayer for a series of different anions at different concentrations. The number of exchanged water molecules was highly dependent on the ionic strength and the type of anion in the buffer solution. However, the entropy change per exchanged water molecule was found to be independent of these two parameters. The water molecules in the polyelectrolyte multilayer have reduced the entropy compared to that of bulk water (≈−1 J mol−1 K−1). A comparison of hydration entropies for free polyelectrolytes and PGA/PAH multilayers suggests that such systems are mainly stabilized by water release during multilayer construction.

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3 citations in Web of Science®
4 citations in Scopus®
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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Biomedical Engineering
Dewey Decimal Classification:170 Ethics
610 Medicine & health
Language:English
Date:2014
Deposited On:03 Oct 2014 14:32
Last Modified:05 Apr 2016 18:23
Publisher:RSC Publishing
ISSN:1744-683X
Publisher DOI:https://doi.org/10.1039/C3SM52489B

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