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Phys Rev Lett. 2007 Aug 10;99(6):066104. doi: 10.1103/PhysRevLett.99.066104. Epub 2007 Aug 08.

Charge regulation as a stabilization mechanism for shell-like assemblies of polyoxometalates.

Physical review letters

Aletta A Verhoeff, Melissa L Kistler, Anish Bhatt, Joe Pigga, Jan Groenewold, Mark Klokkenburg, Sandra Veen, Soumyajit Roy, Tianbo Liu, Willem K Kegel

Affiliations

  1. Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.

PMID: 17930844 DOI: 10.1103/PhysRevLett.99.066104

Abstract

We show that the equilibrium size of single-layer shells composed of polyoxometalate macroions is inversely proportional to the dielectric constant of the medium in which they are dispersed. This behavior is consistent with a stabilization mechanism based on Coulomb repulsion combined with charge regulation. We estimate the cohesive energy per bond between macroions on the shells to be approximately -6kT. This number is extracted from analysis based on a charge regulation model in combination with a model for defects on a sphere. The value of the cohesive bond energy is in agreement with the model-independent critical aggregate concentration. This observation points to a new class of thermodynamically stable shell-like objects. We point out the possible relevance our findings have for certain surfactant systems.

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