Organic-Inorganic Hybrid Supramolecular Gels of Surfactant-Encapsulated Polyoxometalates

A new type of hybrid supramolecular gel derived from a synergic self-assembling of organic and inorganic components has been prepared through encapsulating a series of polyoxometalate (POM) clusters with ammonium surfactants hearing two alkyl chains. Among the general organic solvents we employed, some of surfactant-encapsulated POM (SEP) complexes readily gel with nonpolar solvents. Proper alkyl chain density, alkyl chain length, and shape of POM are proven to be favorable for fabricating stable SEP gels based on the results of critical gelation concentration and transition temperature from gel to solution. In addition, the shape of POM influences the aggregation morphologies of SEPs, stripes and spheres in gel phases, as confirmed by polarizing optical microscopic and scanning electron microscopic images. X-ray diffractions reveal that all the SEPs in gel states possess similar lamellar aggregation structures with POM layer inside and alkyl chain bilayers shielding from the nonpolar solvent oil both sides. The combination of solvent effect, electrostatic. and dipole interaction is thought to be responsible for the formation of SEP gels.