title: Sliding droplets of Xanthan solutions: A joint experimental and numerical study.
abstract: We have investigated the sliding of droplets made of solutions of Xanthan, a stiff rodlike polysaccharide exhibiting a non-Newtonian behavior, notably characterized by a shear thinning viscosity accompanied by the emergence of normal stress difference as the polymer concentration is increased. These experimental results are quantitatively compared with those of Newtonian fluids (water). The impact of the non-Newtonian behavior on the sliding process was shown through the relation between the average dimensionless velocity (i.e. the capillary number) and the dimensionless volume forces (i.e. the Bond number). To this aim, it is needed to define operative strategies to compute the capillary number for the shear thinning fluids and compare with the corresponding Newtonian case. The resulting capillary number for the Xanthan solutions scales linearly with the Bond number at small inclinations, as well known for Newtonian fluids, while it shows a plateau as the Bond number is increased. Experimental data were complemented with lattice Boltzmann numerical simulations of sliding droplets, aimed to disentangle the specific contribution of shear thinning and elastic effects on the sliding behavior. In particular the deviation from the linear (Newtonian) trend is more likely attributed to the emergence of normal stresses inside the non-Newtonian droplet.
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Università di Padova, Via Marzolo, 8, 35131, Padova, Italy. silvia.varagnolo@studenti.unipd.it.
authors.forename: Silvia
authors.initials: S
authors.lastname: Varagnolo
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Università di Padova, Via Marzolo, 8, 35131, Padova, Italy.
authors.forename: Giampaolo
authors.initials: G
authors.lastname: Mistura
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Università di Padova, Via Marzolo, 8, 35131, Padova, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Pierno
authors.affiliation: Department of Physics and INFN, University of "Tor Vergata", Via della Ricerca Scientifica 1, 00133, Rome, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Sbragaglia
keywords: Topical Issue: Multi-scale phenomena in complex flows and flowing matter