  Shear thickening is a phenomenon of significant viscosity increase of
colloidal suspensions. While electrorheological (ER) fluids can be turned into
a solid-like material by applying an electric field, their shear strength is
widely represented by the attractive electrostatic interaction between ER
particles. By shearing ER fluids between two concentric cylinders, we show a
reversible shear thickening of ER fluids above a low critical shear rate (<1
s-1) and a high critical electric field strength (>100 V/mm), which could be
characterized by a modified Mason number. Shear thickening and electrostatic
particle interaction-induced inter-particle friction forces is considered to be
the real origin of the high shear strength of ER fluids, while the applied
electric field controls the extent of shear thickening. The electric
field-controlled reversible shear thickening has implications for
high-performance ER/magnetorheological (MR) fluid design, clutch fluids with
high friction forces triggered by applying local electric field, other
field-responsive materials and intelligent systems.

Soft Condensed Matter