Study On The Self-assembly Of Polyoxomolybdates ({Mo₁₅₄} And {Mo₇₂Fe₃₀}) And The Interaction Between Polyoxomolybdates And Surfactants In Solutions

structures (superficially at least, resemble bilayer vesicles formed by surfactants or lipids in solution) with an average, almost monodispersed radius in water of several tens of nanometers, and composed of more than 1000 POMs. The cohesive energy of per bond between {Mo₇₂Fe₃₀} macroanions on the single-layer shells is approximately 6kT which was extracted from analysis based on a charge regulation model. These findings related to the equilibrium controlling for the size of single-layer shells composed of polyoxometalate macroions in dilute solution could certainly be propitious to surfactant systems such as the vesicles, disc-like micelles, etc. In the fourth chapter, small cations (such as Na⁺, K⁺, Ca²⁺, Ba²⁺, (CH₃)₄N⁺, (C₂H₅)₄N⁺ and (G₄H₉)₄N⁺) )were introduced to the {Mo₇₂Fe₃₀} aqueous solution. The finally dilute solutions are free-extra-electrolytes, being equal to the solutions obtained from dissolving Na⁺-{Mo₇₂Fe₃₀}, K⁺-{Mo₇₂Fe₃₀}, (CH₃)₄N⁺-{Mo₇₂Fe₃₀}, (C₂H₅)₄N⁺-{Mo₇₂Fe₃₀}, (C₄H₉)₄N⁺-{Mo₇₂Fe₃₀}, Ca²⁺-{Mo₇₂Fe₃₀}, and Ba²⁺-{Mo₇₂Fe₃₀} compounds in water. When the large {Mo₇₂Fe₃₀} anionic clusters and cationic counter-ions form superstructures, the conductivity mainly is contributed from the monomers of {Mo₇₂Fe₃₀} anions and cationic cations in solution. Two factors determine the equilibrium size of shells in our studied systems, the charges and the size of the exchanged cationic counter-ions. The higher charges of cationic counter-ions induce the bigger size of shells, however, large size of cationic counter-ions reduce the size of the shells. The size of the shells is subsequently determined by the balance of the two factors, i.e, by minimizing the energy cost of topological defects and the electrostatic self-energy. For the unique self-assembly process of this polyoxomolybdates, certain questions to be analyzed, for example, the driving forces to overcome the Coulomb repulsion among macroanions and attract them together. Prof. Liu had a particular opinion, the self-assembly of the hydrophilic macroions is not mainly attributed to electrostatic interaction, van der Wals force, or chemical bond interaction (the interanionic distance about 1-2 nm) and also the hydrophobic interaction and the hydrogen bond cannot be dominant; therefore, the self-assembly of the hydrophilic macroions is mainly attributed to the charges on their surfaces. So the like-charge attraction does exist in hydrophilic macroionic solutions, and it determines the association of the polyoxomolybdates. That is to say, the nanoscacle polyoxomolybdate anions ("first organized structures") attract each other by sharing the counterions to form the stable vesicle-like aggregations, which is the novel viewpoint between the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory in colloidal chemistry and the Debye-Huckel theory about the stable ions in solution. With regard to this viewpoint about the driving force, there is still no report on the aggregations of amphiphile surfactants. In the fifth chapter, no changes were not found by contrasting the curves of cyclic voltammograms of the before and after aggregation formation of {Mo₁₅₄} and {Mo₇₂Fe₃₀} aqueous solution, which indicated that there were no changes of oxidation and reduction in the formation of the aggregation of {Mo₁₅₄} and {Mo₇₂Fe₃₀}. In another word, these suggested that the vesicle aggregation formation of the polyoxomolybdates is driven by physical forces.