With a focus on electrorheological (ER) activity, the design and modification of ER particles are important to improve the stimuli-responsive properties. Carbon nanomaterial-based composites with abundant morphology and excellent physicochemical properties (excellent electrical and thermal properties, chemical stability, low density, and easy functionalization) have been reported as potential candidates for the development of ER activity. However, the tunable properties and the polarization mechanisms in the ER fluids based on carbon nanomaterials are rarely reported. In recent years, carbonized polydopamine (C-PDA) has been used as a carbon source for the modification of various surfaces due to its excellent adhesion properties. In particular, it exhibits a unique merging of sp²/sp³ carbon, which is advantageous for studying the effect of structure on the ER properties. Therefore, a novel core-shell nanoparticle, consisting of inorganic particles (BaTiO₃, TiO₂, SiO₂) modified with a carbon shell of C-PDA, was designed and prepared. SEM, TEM, XPS, and FT-IR show that not only the shell thicknesses but also the content of sp²/sp³-hybridized carbon are tunable. In addition, the permittivity (ε′) and dielectric loss (ε″) were investigated to gain further insight into the polarization mechanism of carbon nanomaterial-based ER fluids.  
 

ER materials, sp2/sp3 carbon, C-PDA, polarization mechanism