Urchin-like mesoporous TiO2 spheres for enhanced electrorheological performance

A two-step synthesis strategy was employed to synthesize TiO₂ particles with distinct morphologies and crystallinities for electrorheological (ER) fluids. Amorphous TiO₂ (A-TiO₂) and non-calcined urchin-like mesoporous TiO₂ spheres (UMTS) were successfully synthesized via sol-gel and hydrothermal reactions, respectively. Subsequently, calcination further enhanced the crystallinity of the non-calcined UMTS. The TiO₂ particles suspended in silicone oil (10 % volume fraction) were evaluated for their ER performance under varying electric fields (0-3 kV/mm). The ER properties of three variants were characterized in terms of shear stress, shear viscosity, reversibility, and ER efficiency with respect to shear rate under different electric field strengths. As a result, a well-defined chain-like structure is confirmed through an optical microscope (OM). The morphological characteristics of these microstructures were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and Zeta potential, which showed spherical particles (480 nm in average diameter) with urchin-like morphology featuring radially oriented nanotips on their surface. Critically, Fourier transform infrared spectroscopy (FTIR) verified the successful surface modification, confirming the presence of functional groups (OH, Ti-O-Ti) essential for the electrorheological (ER) effect and Brunauer-Emmett-Teller analysis confirmed the high surface area (up to 214 m² g⁻¹) of the synthesized non calcined UMTS, which results to achieve an excellent electrorheological response. X-ray powder diffraction (XRD) analysis revealed the phase conversion from an amorphous to a crystalline anatase structure. Furthermore, the results indicate that heat treatment on crystalline structure significantly influences the ER characteristics, including dielectric loss factor and charge accumulation behavior. The results indicated that the non-calcined UMTS exhibits a higher shear stress, 1270 Pa at 3 kVmm⁻¹ than A-TiO₂ and calcined UMTS. These findings reveal a complex interplay between microstructure and ER performance, offering valuable insights for optimizing ER fluids.