Tunable adhesion using field-activated ``smart" fluids

We demonstrate experimentally that field-responsive magnetorheological fluids can adhere to non-magnetic substrates. The tunable adhesive performance is measured experimentally with pull-off tests, i.e. probe-tack experiments, in which the external magnetic field and fluid geometry are varied. The adhesive force is predicted by a lubrication model which treats the adhesive as a yield stress fluid with field-dependent and inhomogeneous yield stress (caused by the inhomogeneous external magnetic field). The peak adhesive force, the ``work of adhesion" and the mode of failure are all controlled by the field-responsive nature of the magnetorheological fluid forming the adhesive layer.