title: Sliding drops across alternating hydrophobic and hydrophilic stripes.
abstract: We perform a joint numerical and experimental study to systematically characterize the motion of 30 μl drops of pure water and of ethanol in water solutions, sliding over a periodic array of alternating hydrophobic and hydrophilic stripes with a large wettability contrast and a typical width of hundreds of microns. The fraction of the hydrophobic areas has been varied from about 20% to 80%. The effects of the heterogeneous patterning can be described by a renormalized value of the critical Bond number, i.e., the critical dimensionless force needed to depin the drop before it starts to move. Close to the critical Bond number we observe a jerky motion characterized by an evident stick-slip dynamics. As a result, dissipation is strongly localized in time, and the mean velocity of the drops can easily decrease by an order of magnitude compared to the sliding on the homogeneous surface. Lattice Boltzmann numerical simulations are crucial for disclosing to what extent the sliding dynamics can be deduced from the computed balance of capillary, viscous, and body forces by varying the Bond number, the surface composition, and the liquid viscosity. Beyond the critical Bond number, we characterize both experimentally and numerically the dissipation inside the droplet by studying the relation between the average velocity and the applied volume forces.
authors.affiliation: Department of Physics and INFN, University of "Tor Vergata," Via della Ricerca Scientifica 1, I-00133 Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Sbragaglia
authors.affiliation: Department of Physics and INFN, University of "Tor Vergata," Via della Ricerca Scientifica 1, I-00133 Rome, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Biferale
authors.affiliation: SCAI, SuperComputing Applications and Innovation, Department CINECA, Via dei Tizii, I-00185 Roma, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Amati
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Varagnolo
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Ferraro
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Mistura
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Pierno
mesh_terms: D003198:Computer Simulation; D017276:Friction; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008422:Materials Testing; D044085:Microfluidics / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D009038:Motion; D009991:Oscillometry / Q000379:methods*; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water