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. 2015 Aug 7;6:7986. doi: 10.1038/ncomms8986

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(a) Comparison of time-resolved evolution of the spread factor L_c/D on samples of h=50 μm with different viscosity. The We is 20. The values of L_c/D in the retraction stage are dependent on the oil viscosity, displaying a substrate-dependent retraction behaviour. (b) Calculated retraction velocity ν_re as a function of We indicating that the retraction velocity is independent of the oil viscosity in the superhydrophobic-like bouncing regime, that is, We≲10. By contrast, with the rupture of thin air cushion, that is, We≳18, the retraction velocity becomes highly dependent on the oil viscosity. (c) The droplet retraction rate ν_re/D_max as a function of viscous time scale τ_μ. The measured retraction rates overlap well with the scaling of , where is the viscous time scale (corresponding to two datasets with Oh>1). For Oh≈0.86 (μ_o=0.15 Pa s), the retraction rates diverge from the master curve because the inertia force and viscous force are comparable in this case.

Inline graphic — (a) Comparison of time-resolved evolution of the spread factor L_c/D on samples of h=50 μm with different viscosity. The We is 20. The values of L_c/D in the retraction stage are dependent on the oil viscosity, displaying a substrate-dependent retraction behaviour. (b) Calculated retraction velocity ν_re as a function of We indicating that the retraction velocity is independent of the oil viscosity in the superhydrophobic-like bouncing regime, that is, We≲10. By contrast, with the rupture of thin air cushion, that is, We≳18, the retraction velocity becomes highly dependent on the oil viscosity. (c) The droplet retraction rate ν_re/D_max as a function of viscous time scale τ_μ. The measured retraction rates overlap well with the scaling of , where is the viscous time scale (corresponding to two datasets with Oh>1). For Oh≈0.86 (μ_o=0.15 Pa s), the retraction rates diverge from the master curve because the inertia force and viscous force are comparable in this case.