Salt softening of polyelectrolyte multilayer microcapsules

Olga V. Lebedeva, Byoung Suhk Kim, Krasimir Vasilev, Olga I. Vinogradova

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49 Citations (Scopus)


By using a combination of atomic force and confocal microscopy, we explore the effect of 1:1 electrolyte (NaCl) on the stiffness of polyelectrolyte microcapsules. We study the "hollow" and "filled" (with polystyrene sulfonate) capsules. In both cases the shells are composed of layers of alternating polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH). The stiffness of both "hollow" and "filled" capsules was found to be largest in water. It decreases with salt concentration up to ∼3 mol/L and gets quasi-constant in more concentrated solutions. The "filled" capsules are always stiffer than "hollow." The observed softening correlates with the salt-induced changes in morphology of the multilayer shells detected with the scanning electron microscopy. It is likely that at concentrations below ∼3 mol/L the multilayer shell is in a "tethered" state, so that the increase in salt concentration leads to a decrease in number of ionic cross-links and, as a result, in the stiffness. In contrast, above the critical concentration of ∼3 mol/L multilayer shells might be in a new, "melted," state. Here the multilayer structure is still retained, but sufficient amount of ionic cross-links is broken, so that further increase in salt concentration does not change the capsule mechanics. These ideas are consistent with a moderate swelling of multilayers at concentrations below ∼3 mol/L and significant decrease in their thickness in more concentrated solutions measured with surface plasmon spectroscopy.

Original languageEnglish
Pages (from-to)455-462
Number of pages8
JournalJournal of Colloid and Interface Science
Issue number2
Publication statusPublished - 15 Apr 2005
Externally publishedYes


  • Multilayer microcapsules
  • Polyelectrolytes
  • Salt softening


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