Carina Bojer

Direct Synthesis of Inverse Hexagonally Ordered Diblock Copolymer/ Polyoxometalate Nanocomposite Films

Nanostructured inverse hexagonal polyoxometalate composite films were cast directly from solution using poly(butadiene-block-2-(dimethylamino)ethyl methacrylate) (PB-b-PDMAEMA) diblock copolymers as structure directing agents for phosphomolybdic acid (H(3)[PMo(12)O(40)], H(3)PMo). H(3)PMo units are selectively incorporated into the PDMAEMA domains due to electrostatic interactions between protonated PDMAEMA and PMo(3-) anions. Long solvophilic PB chains stabilized the PDMAEMA/H(3)PMo aggregates in solution and reliably prevented macrophase separation. The choice of solvent is crucial. It appears that all three components, both blocks of the diblock copolymer as well as H(3)PMo, have to be soluble in the same solvent which turned out to be tetrahydrofuran, THF. Evaporation induced self-assembly resulted in highly ordered inverse hexagonal nanocomposite films as observed from transmission electron microscopy and small-angle X-ray scattering. This one-pot synthesis may represent a generally applicable strategy for integrating polyoxometalates into functional architectures and devices.

Template Removal via Boudouard Equilibrium Allows for Synthesis of Mesostructured Molybdenum Compounds

Oxidative thermal removal of the polymeric templates is not trivial for molybdenum oxides and hampers mesostructuring of this material. At ambient oxygen fugacity, MoVI is the thermodynamically stable oxidation state and sublimation of MoO3 leads to a quick loss of the mesostructure through Oswald ripening. Taking advantage of the Boudouard equilibrium allows to fix the oxygen fugacity at a level where non-volatile MoO2-x is stable while carbonaceous material may be oxidized by CO2 . Mesostructured MoO2-x can be chemically converted into MoO3 or MoN under retention of the mesostructure.

Packing of Cylindrical Keggin-Type Polyoxometalate Hybrid Micelles as a Function of Aspect Ratio

Abstract The packing of cylindrical Keggin-Type polyoxometalate hybrid micelles and its influence on specific surface area was studied as function of aspect ratio. Core-crosslinked cylindrical poly(butadiene-block-2-vinylpyidine) (PB-b-P2VP) micelles were used as templates for mesostructuring phosphomolybdic acid (H3PMo12O40). Prior to hybrid formation the length of the cylindrical PB-b-P2VP micelles was adjsuted by sonication. Depending on the aspect ratio of the cylinders a remarkable and unexpected evolution of specific surface areas was observed. The changes in the specific surface area could be explained by a series of scanning electron microscopy and transmission electron microscopy images and were related to the packing of the 1D nanoobjects.