title: Deviation of sliding drops at a chemical step.
abstract: The motion of partially wetting liquid drops in contact with a solid surface is strongly affected by contact angle hysteresis and interfacial pinning. However, the majority of models proposed for drops sliding over chemical surface patterns consistently neglect the difference between advancing and receding contact angles. In this article, we present a joint experimental and numerical study of the interaction of gravity-driven drops with a chemical step formed at the junction between a hydrophilic and a hydrophobic region. It demonstrates the strong impact of a contact angle hysteresis contrast on the motion of drops at a linear chemical step. Surprisingly, the smallest driving force required to drag the drop across the step onto the lower hydrophobic surface is not observed at a right angle of incidence. Our model reveals that the non-monotonous response of this passive drop 'filter' is solely due to the higher advancing contact angle on the lower surface, and creates an instance where drop motion is affected by dissipation at the contact line rather than by surface energy.
authors: Department of Mechanical Engineering, University of Edinburgh, Edinburgh EH9 3FB, UK. ciro.semprebon@ed.ac.uk.
authors: Ciro
authors: C
authors: Semprebon
authors: Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy. giampaolo.mistura@unipd.it.
authors: Silvia
authors: S
authors: Varagnolo
authors: Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy. giampaolo.mistura@unipd.it.
authors: Daniele
authors: D
authors: Filippi
authors: Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy. giampaolo.mistura@unipd.it.
authors: Luca
authors: L
authors: Perlini
authors: Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy. giampaolo.mistura@unipd.it.
authors: Matteo
authors: M
authors: Pierno
authors: Experimental Physics, Saarland University, 66123 Saarbrücken, Germany.
authors: Martin
authors: M
authors: Brinkmann
authors: Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy. giampaolo.mistura@unipd.it.
authors: Giampaolo
authors: G
authors: Mistura