We investigate the dynamics of freely expanding liquid sheets prepared with fluids with different rheological properties: (i) Viscous fluids with a zero-shear viscosity ${\eta }_0$ in the range $1–1000\mathrm{mPa}\mathrm{s}$ and (ii) viscoelastic fluids whose linear viscoelastic behavior in the frequency range $0.1–100$ rad/s can be accounted for by a Maxwell fluid model, whose characteristic elastic modulus $G_0$, relaxation time $\tau$, and zero-shear viscosity ${\eta }_0=G_0\tau$, can be tuned over several orders of magnitude. The sheets are produced by a drop of fluid impacting a small cylindrical solid target. For viscoelastic fluids, we show that, when $\tau$ is shorter than the typical lifetime of the sheet ($\sim 10$ ms), the dynamics of the sheet is similar to that of Newtonian viscous liquids with equal zero-shear viscosity. In that case, for little viscous samples (${\eta }_0\lesssim 30$ mPa s), the maximal expansion of the sheet $d_{\max }$ is independent of ${\eta }_0$, whereas for more viscous samples, $d_{\max }$ decreases as ${\eta }_0$ increases. We provide a simple model for the dependence of the maximal expansion of the sheet with the viscosity that accounts well for our experimental data. By contrast, when $\tau$ is longer than the typical lifetime of the sheet, the behavior drastically differs. The sheet expansion is strongly enhanced as compared to that of viscous samples with comparable zero-shear viscosity, but is heterogeneous with the occurrence of cracks, revealing the elastic nature of the viscoelastic fluid.

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• Complex fluids
• Interfacial flows
• Non-Newtonian fluids
• Viscoelasticity
• Hydrogels
• Micelles
• Surface tension effects
• Imaging & optical processing
• Rheology techniques