Magnetorheological (MR) fluids are colloidal suspensions of magnetizable particles that exhibit an increase in the yield stress and in the apparent viscosity when a magnetic field is applied. It has been shown previously that MR fluids can also be used for field-controlled static adhesion to non-magnetic surfaces. For example, a thin layer of MR fluid can be used to adhere a piece of plastic to a ceramic tile, simply by turning on a magnetic field across the fluid layer. Here we demonstrate the important role surface tension plays in this adhesion and that the adhesive property is not related to the shear resistance of the field-dependent yield stress, as previously proposed.

1. •Carlos S. Orellana and Heinrich M. Jaeger, “The Role of Surface Tension in Magnetorheological Adhesion”, Soft Matter 9, 8519 2013. pdf
   

Our results suggest that the current theoretical description of adhesion with MR fluids, based on a continuum fluids dynamics plus a field-dependent yield stress is not complete and they call for new physical interpretation of experimental work related to measurement and control of normal forces in such systems. We expect that the same capillary forces related to menisci at the particle scale, demonstrated here for MR fluids, also can become important for adhesion using electric fields with ER or GER fluids.