Nanocasting of Inverse ABC Phases Particles

NMR spectroscopic analysis finally proved that the poly(ethylene oxide) blocks are firmly anchored in the inorganic phase rather than being located at the interphase adjacent to the hydrophobic domains. Solid-state NMR spectroscopy revealed that this anchoring leads to a substantial hindrance of the conformational mobility in the poly(ethylene oxide) chains compared with the relatively mobile hydrophobic poly(isoprene) [44]. 

Two possible scenarios can be envisaged for the structure of the hybrid material (see Fig. 11). The poly(ethylene oxide) block, albeit strongly interacting and partially penetrating, forms a pure PEO layer at the interface to the hydrophobic poly(isoprene) (Fig. 11, left-hand sketch) ( three-phase system). The other possibility is the complete dissolution of the PEO chains in the aluminosilicate, which results in the two-phase system depicted in the right-hand sketch of Fig. 11. Spin-diffusion NMR experiments showed that there appears to be no dynamic heterogeneity in the poly(ethylene oxide) chains, as would be expected for a three-phase system, giving rise to the conclusion that the hydrophilic 

This approach towards nanostructured inorganic-organic hybrid materials is the first one to allow the synthesis of inverse-topology systems, in which the hydrophobic polymer blocks represent the outside of the microphase-separated structure. After solidification of the inorganic sol, the hydrophobic phase can be swollen with organic solvents. This procedure allows the isolation of colloidal objects, such as spheres or ceramic rods (see Fig. 12), from one another, which are sterically stabilized, because the hydrophihc block is firmly anchored in the ceramic material [45]. 

The position of the hydrophilic poly(ethylene oxide) (PEO) headgroups in ABCs and nonionic surfactant templates bears important imphcations with respect to the overall pore structure of the resulting porous material. The PEO chains can be assumed to be firmly anchored and molecularly dispersed within the silica matrix, hence giving rise to substantial microporosity of the meso-porous system. The following section is aimed at describing the pore structure of nonionically templated mesoporous ceramics more exactly. 

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