Liquid trains in a tube

Trains of juxtaposed drops in a tube are described and found to move spontaneously, in setting conditions. because of their asymmetry. We focus on the coating properties of these devices, and show in particular that highly viscous species can be (self-) transported, thanks to the lubricating film left by the first drop. Different properties of these systems are finally displayed, which stress their versatility towards microfluidics applications.