Donnan Equilibrium and Osmotic Pressure in Hollow Polyelectrolyte Microcapsules

David Haložan,¹* Gleb B. Sukhorukov,² Milan Brumen,^1,3 Edwin Donath,⁴ Helmuth Möhwald^5
1 University of Maribor, Slom{kov trg 15, SI-2000 Maribor, Slovenia
² Department of Materials, Queen Mary University of London, Mile End Road, E1 4NS, London, UK
³ Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
⁴ Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstraße 16–18, 04107 Leipzig, Germany
⁵ Max-Planck-Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476 Golm, Germany
  E-mail: david.halozan@uni-mb.si, Phone: +386 2 2293 795, Fax: +386 2 2518 180

Abstract
A simple theoretical model of the Donnan equilibrium is applied to studies of distributions of ions between the external and internal volumes of hollow polyelectrolyte capsules as well as of concomitant osmotic pressure load on a capsule wall resulting from these distributions and the presence of polyanion. The model system consist of dispersed polyelectrolyte capsules in an electrolyte solution whereby two cases are considered with respect to the presence of the polyanion, either in the inner or external solution. It is assumed that the capsule wall is impermeable to polyanion, but water and all ions can freely penetrate. The model predictions are summarized by presenting the difference between the external pH, the pH of the inner solution and the osmotic pressure difference across the capsule wall, both in the dependence of sodium chloride concentration.

Keywords: Polyelectrolyte hollow capsule, Donnan equilibrium, osmotic pressure.