Preparation and electrorheological properties of a La-doped MOF-Ti composite encapsulated with TiO₂

Electrorheological fluids (ERFs) are intelligent suspensions capable of rapidly transitioning from liquid-like to solid-like states under an applied electric field. In this work, titanium dioxide-coated, lanthanum-doped metal-organic framework (MOF) nanoparticles (La-MOF@TiO₂) were synthesized via a combined solvothermal-hydrolysis method as a high-performance electrorheological (ER) material. The incorporation of lanthanum ions allows precise tuning of the material's dielectric response, and structural stability, while the titania coating forms a tunable core-shell architecture, demonstrating unique potential in ER applications. SEM and TEM analyses, together with elemental mapping, were employed to examine the morphology, microstructure, and component distribution of the samples. Phase composition and chemical states were determined by XRD, FT-IR, and XPS. Nitrogen adsorption-desorption was used to evaluate changes in surface area and pore characteristics, and dielectric spectroscopy was conducted to probe polarization behavior. The ER properties of La-MOF@TiO₂-based ERFs were assessed using a HAAKE rotational rheometer. A shear-stress plateau of 400 Pa was obtained for MLa-80@TiO₂ nanocomposites at an electric field strength of 3 kV mm^-1 and a particle mass fraction of 10 wt%. The results indicate that, compared to solely lanthanum-doped MOF particles, the La-MOF@TiO₂ nanocomposites possess superior electrical properties and excellent ER characteristics.