title: Stretching of viscoelastic drops in steady sliding.
abstract: The sliding of non-Newtonian drops down planar surfaces results in a complex, entangled balance between interfacial forces and non-linear viscous dissipation, which has been scarcely inspected. In particular, a detailed understanding of the role played by the polymer flexibility and the resulting elasticity of the polymer solution is still lacking. To this aim, we have considered polyacrylamide (PAA) solutions of different molecular weights, suspended either in water or in glycerol/water mixtures. In contrast to drops of stiff polymers, drops of flexible polymers exhibit a remarkable elongation in steady sliding. This difference is most likely attributed to variation of viscous bending as a consequence of variation of shear thinning. Moreover, an "optimal elasticity" of the polymer seems to be required for this drop elongation to be visible. We have complemented experimental results with numerical simulations of a viscoelastic FENE-P drop. This has been a decisive step to unraveling how a change of the elastic parameters (e.g. polymer relaxation time, maximum extensibility) affects the dimensionless sliding velocity.
authors.affiliation: Dipartimento di Fisica e Astronomia "Galileo Galilei"- DFA, Università di Padova, via Marzolo, 8-35131 Padova PD, Italy. matteo.pierno@unipd.it.
authors.forename: Silvia
authors.initials: S
authors.lastname: Varagnolo
authors.forename: Daniele
authors.initials: D
authors.lastname: Filippi
authors.forename: Giampaolo
authors.initials: G
authors.lastname: Mistura
authors.forename: Matteo
authors.initials: M
authors.lastname: Pierno
authors.forename: Mauro
authors.initials: M
authors.lastname: Sbragaglia