Simultaneous observations of microgap flow behavior and microstructure of electro-rheological nano-suspensions based on titanium dioxide nano-particles

Abstract

Electro-rheological (ER) nano-suspensions based on titanium dioxide nano-particles with particle diameter around 400 nm and a chemically modified silicone oil with a viscosity of 0.04 Pa·s were prepared. Microgap flow behavior in the absence of an external electric field and the ER responses were investigated in relation to the microstructure observed in the quiescent state. The effects of the continuous phase of suspending oil and particle volume fraction were reported for the nano-suspensions. For the modified silicone oil-based nano-suspensions of 8.8 and 12 vol %, no plateau stresses were observed, whereas a plateau stress around 5 Pa was found only for the nano-suspension of 20 vol %. On the other hand, the ER effect of the modified silicone oil-based nano-suspension of 20 vol % was comparable to that of the silicone oil-based nano-suspension of 12 vol %. Simultaneous optical observations with the ER effect were also performed for the nano-suspension of 20 vol %. The effects of shear rate and time on the shear stress and flow behavior in the presence (or absence) of the dc electric field were reported, showing unexpected reduction of the ER effect and the shear thinninglike behavior with flow instability at higher shear rates. Possible factors for improving the ER effect were discussed in the present paper.