Structure−Property Correlation in Iron Oxide Nanoparticle−Clay Hybrid Materials

Heterostructures between montmorillonite and embedded α-Fe 2 O 3 nanoparticles are explored to create new hybrid particles with high magnetic response and magnetic-field induced tunability. α- Fe 2 O 3 nanoparticles are hybridized to montmorillonite clays by using an intercalation technique. Also, stable aqueous fluids consisting of the heterostructured particles are prepared and the rheology of the fluids under external magnetic field is examined. When α- Fe 2 O 3 nanoparticles are embedded in the interlayer space of montmorillonite clays, the magnetization per Fe atom increases at most 60 times. This unique combination of the magnetization and the coercivity is traced to the suppressed growth of embedded α-Fe 2 O 3 nanoparticles by the aluminosilicate layers, leading to the size control, anisotropic magnetic interaction, and uniaxial stress of two-dimensionally distributed α-Fe 2 O 3 nanoparticles. Furthermore, high magnetization of heterostructured particles leads to strong dependence of fluids’ viscosity on the external magnetic field. The present study indicates that the new heterostructured particles have unique magnetic field-dependent properties that are not attainable in individual clay or iron oxide particles.