  In this article, we propose, with the aid of detailed experiments and scaling
analysis, the existence of magneto-elastic effects in the impact hydrodynamics
of non-Newtonian ferrofluid droplets on superhydrophobic (SH) surfaces in
presence of a magnetic field. The effects of magnetic Bond number (Bom), Weber
number (We), polymer concentration and magnetic nanoparticle (Fe3O4)
concentration in the ferrofluids were investigated. In comparison to Newtonian
ferrofluid droplets, addition of polymers caused rebound suppression of the
droplets relatively at lower Bom for a fixed magnetic nanoparticle
concentration and We. We further observed that for a fixed polymer
concentration and We, increasing magnetic nanoparticle concentration also
triggers earlier rebound suppression with increasing Bom. In the absence of the
magnetic nanoparticles, the non-Newtonian droplets do not show rebound
suppression for the range of Bom investigated. Likewise, the Newtonian
ferrofluids show rebound suppression at large Bom. This intriguing interplay of
elastic effects of polymer chains and the magnetic nanoparticles, dubbed as the
magneto-elastic effect is noted to lead to the rebound suppression. We
establish a scaling relationship to show that the rebound suppression is
observed as manifestation of onset of magneto-elastic instability only when the
proposed magnetic Weissenberg number (Wim) exceeds unity. We also put forward a
phase map to identify the various regimes of impact ferrohydrodynamics of such
droplets, and the occurrence of the magneto-elastic effect.
