Anisotropy of field-controlled shear viscosity of dipolar fluids

We numerically study the anisotropic viscous response of dipolar hard spheres in the presence of an electric field. We find that the shear viscosity is sensitive to both the strength and orientation of the field relative to the shearing direction. The effect on the viscosity is strongest when the field is oriented in the shear gradient direction. We investigate the structure of the fluid in detail to explain the mechanism for the changes in viscosity, and show that the reorientation of chain-like clusters plays a crucial role. We show that the anisotropy arises from the polarization of the fluid induced by the field, leading to the orientation of chain-like clusters along the direction of the field.