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Swelling of Polyelectrolyte Multilayers: The Relation Between, Surface and Bulk Characteristics.
Maximilian Zerball1, André Laschewsky2,3, Regine von Klitzing1
1Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin , Strasse des 17. Juni 124, 10623 Berlin, Germany.
The odd-even effect in polyelectrolyte multilayers (PEMs) depends on the outermost layer and environmental conditions. Two distinct effects, surface and bulk, were identified, influencing PEM swelling behavior differently in humid air versus liquid water.
Area of Science:
- Materials Science
- Surface Chemistry
- Polymer Science
Background:
- Polyelectrolyte multilayers (PEMs) exhibit swelling behavior influenced by their outermost layer, known as the odd-even effect.
- Understanding water uptake in PEMs requires differentiating between void water and swelling water fractions.
Purpose of the Study:
- To investigate the odd-even effect in poly(styrene sodium sulfonate)/poly(diallyl-dimethylammonium chloride) (PSS/PDADMAC) PEMs.
- To differentiate and analyze void water and swelling water contributions to PEM swelling.
- To explore the environmental dependence of the odd-even effect.
Main Methods:
- Ellipsometry, atomic force microscopy (AFM), and X-ray reflectometry (XRR) were employed to study PEMs.
- Neutron reflectometry concepts for separating water fractions were adapted for ellipsometry.
- PEMs were analyzed under varying relative humidity (1%, 30%, 95% RH) and in liquid water.
Main Results:
- Two types of odd-even effects were identified: a surface-odd-even effect in humid air and a bulk-odd-even effect in liquid water.
- The bulk-odd-even effect is linked to osmotic pressure between the PEM and surrounding water.
- The amount of void water was found to be independent of the terminated layer and PEM thickness.
Conclusions:
- The odd-even effect in PEM swelling is environmentally sensitive, manifesting differently in air versus water.
- Distinct surface and bulk odd-even effects influence PEM hydration.
- Void water content does not correlate with the observed odd-even effects.
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