Effect of pH and Salt on the Stiffness of Polyelectrolyte Multilayer Microcapsules

By using a combination of atomic force and confocal microscopy, we explore the effect of pH and salt on the stiffness of polyelectrolyte microcapsules with shells composed of strong polyanions and weak polycations. The stiffness of the capsules was found to be largest in water. It decreases slightly...

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Bibliographic Details
Published in:Langmuir 2004-03, Vol.20 (7), p.2874-2878
Main Authors: Lulevich, Valentin V, Vinogradova, Olga I
Format: Article
Language:English
Subjects:
Capsules - chemistry
Electrolytes - chemistry
Hydrogen-Ion Concentration
Microscopy, Atomic Force
Microscopy, Confocal
Microspheres
Polymers - chemistry
Sodium Chloride - chemistry
Surface Properties
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Summary:By using a combination of atomic force and confocal microscopy, we explore the effect of pH and salt on the stiffness of polyelectrolyte microcapsules with shells composed of strong polyanions and weak polycations. The stiffness of the capsules was found to be largest in water. It decreases slightly with added salt and gets much smaller both in acidic and in alkaline solutions. The moderate softening of the capsules in electrolyte solutions indicates that even high salt concentration does not significantly dissociate polyelectrolytes in the multilayer. The dramatic softening of the capsules at high pH probably reflects a decrease in the charge density of a polycation, which leads to a reduction in the number of ionic cross-links. In contrast, low stiffness of the capsules in acidic solutions seems to be connected mostly with the enhanced permeability of the multilayer shell.
ISSN:0743-7463
1520-5827
DOI:10.1021/la049934h