Yield stress fluids, including gels and pastes, are effectively fluid at high stress and solid at low stress. In liquid-solid impacts, these fluids can stick and accumulate where they impact, motivating several applications of these rheologically-complex materials. Here we use high-speed imaging to experimentally visualize liquid-solid impact of yield stress fluids on heated dry surfaces. At low temperatures, yield stress fluids tend to stick and leave a coating layer. At sufficiently high temperatures, sticking no longer occurs. Instead, fluid jets and droplets seem to avoid contacting the solid surface all together, sometimes bouncing off with redirected momentum. Our observations suggest that this is due to the Leidenfrost effect, wherein a vapor film is created between the fluid and the hot surface. This vapor layer allows for curious and unexpected breakup dynamics not seen on cold surfaces.
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