Charge Regulation as a Stabilization Mechanism for Shell-Like Assemblies of Polyoxometalates

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 ÿ6kT. 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.

Sheet-like assemblies of spherical particles with point-symmetrical patches

“…16 Once a critical size of the sheet is reached (∼1000 particles), the sheets are potentially eligible to fold into shells due to large fluctuations. We have shown here that sheet-like structures in Keplerate-type POMs are kinetically stabilized due to their preferred growth in 2D, as dictated by the icosahedral point symmetry of their patches.…”

Polyoxometallate als Bausteine für funktionelle Nanosysteme

“…[107] Die Größe der "Brombeer"-Strukturen kann aus dem Zeta-Potential und der Kohäsionsenergie berechnet werden. [108] Die Gleichgewichtsgröße wird von der renormalisierten Ladungsdichte bestimmt, die ihrerseits durch die Kondensation von Gegenionen reguliert wird. Dies führt zu der theoretischen Vorhersage, dass die Größe der Hülle linear mit dem Kehrwert der Dielektrizitätskonstante des Mediums zunimmt.…”

“SOFT OXOMETALATES” (SOMs): A VERY SHORT INTRODUCTION

“…[8] To explain such observation a simple model was proposed. This model proposes: 1. the driving force for the formation of SoFoSOM blackberries is pair-wise additive attractive interaction between the constituent POMs.…”