Ferrofluid droplets in planar extensional flows: Droplet shape and magnetization reveal novel rheological signatures of ferrofluid emulsions

Abstract

By subjecting a ferrofluid emulsion to an external magnetic field, the flow at the droplet scale is altered, resulting in significant changes in the emulsion's rheological behavior. We present the first study of the rheological response of a dilute ferrofluid emulsion under extensional flow. Our findings reveal that at the microscopic level, the droplets experience a field-induced internal torque that leads to a complex non-symmetric stress tensor. We identify the remarkable presence of shear stresses within a material experiencing a pure extensional flow.