Fluidisation of yield stress fluids under vibration

Motivated by the industrial processing of chocolate, we study experimentally fluidisation a sessile drop yield-stress fluid on pre-existing layer same under vertical sinusoidal oscillations. We compare behaviours molten chocolate and Carbopol which are both shear-thinning with similar yield stress but exhibit very different elastic properties. find that these materials spread when forcing acceleration exceeds threshold is determined initial deposition process. However, height reduction due to spreading typically at least three times greater in than forcing. Moreover, two behaviours: whereas exhibits slow long-term spreading, rapidly relaxes its new equilibrium shape an enlarged footprint. This insensitive history In addition, performs large-amplitude oscillations frequency, above below threshold. investigate viscoelastic provide evidence complex nonlinear behaviour vicinity fact, for accelerations threshold, our automatically adjusts remain stress. discuss how vibrated-drop experiment offers powerful approach probing transition elastoviscoplastic fluids.