Electrorheology of methacrylic acid functionalized titania nanotubes in silicone oil

Titanium oxide (TiO 2 ) nanotubes functionalized with a shell of methacrylic acid were synthesized and applied to prepare electrorheological (ER) suspensions in this study. Performance was compared with the bare TiO 2 nanotubes and simple spherical commercial nanoparticles. ER performance was evaluated under electric field from 0 to 5 kV/mm using shear and yield stress measurements. The organic shell provided electrical insulation minimizing joule effect during operation and preventing overheating, rendering it more suitable for real life technological applications, while also improving the suspension stability. This came at the cost of some of the ER effect intensity which is directly influenced by the conductivity. The high aspect ratio of the tubes still led to a net performance enhancement compared to the commercial control. From this comparison, a 3.5-fold increase of the rheological response to the field was obtained just from the explored morphology. These findings demonstrate that methacrylic acid functionalization enables safer and more stable ER fluids while preserving superior performance compared to spherical nanoparticles.