Synthesis of silica bearing sulfobetaine and sulfonic groups and their electrorheological response

Organically modified silica bearing amino groups (SiO2-NH2) was prepared by the simple sol-gel procedure followed by treatment with butanesultone to produce zwitterionic silica bearing sulfobetaine groups (SiO2-SB). This particle was then treated with sulfuric acid to prepared particles carrying both sulfonic acid and ammonium salt (SiO2-SO3H). These particles were characterized by different methods and dispersed in silicone oil (15 wt%) to evaluate the electrorheological (ER) performance. Thermogravimetric (TG) analysis, zeta potential and Fourier transform infrared (FTIR) spectroscopy confirmed the structure of the modified silica. The ER response was evaluated using controlled shear stress (CSR) and oscillatory mode. The SiO2-NH2 and SiO2-SB based fluids displayed the highest shear stress at low shear rate even without an applied electric field. However the higher ER efficiency and lower leakage current was observed for the fluid containing SiO2-SO3H. From dielectric analysis, it was demonstrated that the zwitterionic SiO2-SB particle provided faster relaxation time and larger permittivity difference. Thus, it is possible to conclude that the lower viscosity of the SiO2-SO3H based fluid without electric field also plays an important role for a good ER efficiency. Both SiO2-SB and SiO2-SO3H particles are suitable for producing ER fluids due to their better dielectric properties and relaxation time. The former also presented better sedimentation stability.