Examination of the Amphiphilic Properties of Dumb-bell-Shaped Polyoxometalate-Organic Hybrid Materials.

摘要

Polyoxometalate (POM) molecular clusters exhibit a great diversity of sizes, nuclearities, and shapes providing singular properties for forming hybrid materials and supramolecules. These hybrids are formed by linking one, two and three Wells-Dawson type clusters, [P2V3W 15O62]9--, with different linear (TRIS)-linker ligands between the TRIS moieties. Laser light scattering (LLS) reveals the presence of self-assembled vesicular structures in water/acetone mixed solvents, while the vesicle size increases with increasing acetone content, suggesting a charge regulated process. The hybrids show amphiphilic behaviors like surfactants, but also demonstrate different properties such as the unusual large entropy contribution to the vesicle formation and the involvement of amphiphilic tetrabutylammonium (TBA) counter-ions, due to their unique large polar head groups, complex organic linkers and their special molecular architectures. Bending energy theory and elastic constants are used to successfully explain the vesicle formation and stability in solution. The vesicle size increases in proportion with the elastic modulus (kc) and reveals an important role of the organic ligands on the process during vesicle formation. Interfacial behavior is shown for all the five heterotungstate dumb-bell shape hybrids with the water sub-phase and form thin films or monolayers similar to some ionic surfactants. In addition, calorimetric studies reveal an important L/S interface adsorption. The occupied molecular area shows a different molecular binding orientation. The space between both polar heads dictates a packing and horizontal molecular adsorption interface. Numerous astonishing and fascinating phenomena have been observed in these novel hybrid systems.