Control of Inorganic Layer Thickness in Self-Assembled Iron Oxide/Surfactant Composites

Abstract

The synthesis and characterization of ordered, lamellar, iron oxide/surfactant composites in which the iron oxide layer thickness is selectively varied are presented. These new materials are prepared by the controlled precipitation and hydrolysis of aqueous iron cations into self-assembled iron/surfactant arrays. The use of redox chemistry to alter the solubility of iron oxide and thus control hydrolysis, solubility, and inorganic layer thickness is a key feature of the synthesis procedure. The composites show a layered structure as determined by X-ray diffraction and can be produced with approximately 3 to nearly 20 Å of iron oxide in alternation with surfactant bilayers. For samples with 10 Å or thicker iron oxide layers, magnetic susceptibility measurements and Mössbauer spectroscopy indicate the presence of superantiferromagnetic domain structures with smaller domains observed in samples with thinner layers. The results are a first step toward the simple design of hierarchical nanostructured magnetic materials using cooperative, three-dimensional inorganic/organic self-organization.