Electrorheological properties of suspensions of silica nanoparticles modified by urea and N,N-dimethylformamide

In this study, electrorheological (ER) behaviour of suspensions of silica nanoparticles treated with urea and N,N-dimethylformamide in DC electric field has been investigated. While the ER effect of the neat silica was very low, its modification improved compatibility of the solid and liquid phase and considerably increased ER activity of the system. The dependence of the dynamic yield stress τ0 on the electric field strength E obeyed the power law τ0 = qEα, where the exponent α depended on the intensity of solidification of the suspension in the electric field. The 25 wt.% fluid showed a high absolute value of dynamic yield stress, but its relative increase due to high field-off value was much lower than for 20 wt.% suspension, so the latter is more suitable for practical applications.