Ultra-Soft Liquid-Ferrofluid Interfaces

Soft interfaces are ubiquitous in nature, governing quintessential hydrodynamics functions, like lubrication, stability, and cargo transport. It is shown here how a magnetic pressure at a magnetic-nonmagnetic fluid interface results in an ultra-soft interface with nonlinear elasticity and tunable viscous shear properties. The balance between magnetic pressure, viscous stress, and Laplace pressure results in a deformed and stable liquid-in-liquid tube with apparent elasticity in the range of 2-10 kPa, possibly extended by a proper choice of liquid properties. Such highly deformable liquid-liquid interfaces of arbitrary shape with vanishing viscous shear open doors to unique microfluidic phenomena, biomaterial flows and complex biosystems mimicking. A deformable, soft, and slippery liquid-ferrofluid interface is engineered, which deforms reversibly (at different flow rates) and results in a novel fluid-(soft) structure interaction. The experiments are backed by an analytical model that predicts deformations driven by the balance between magnetic pressure and viscous shear stress. The liquid-liquid interface can be employed for biomimicking, flow chemistry, and interface fluid physics applications. image