In this work, we study theoretically the thickness of a liquid film (typically made of a surfactant solution) pulled out of a bath at constant speed in the absence of gravity, when it features a viscous or an elastic interfacial rheology. We show that a purely viscous rheology does not lead to the extraction of a steady state film of constant thickness. In contrast, the thickness of the film is well defined in the elastic case, which allows us to compute it. This thickness depends on the capillary number of the experiment, and on the elasticity of the interface. It is always lower than or equal to that obtained for an incompressible interface predicted by Frankel (Mysels, Shinoda and Frankel, Soap Films: Studies of their Thinning and a Bibliography, 1959), which is recovered in the limit of an arbitrary large elasticity.

T1 topological rearrangement, i.e. switching of neighbouring bubbles in a liquid foam, is the elementary process of foam dynamics, and it involves film disappearance and generation. It has been studied extensively as it is crucial in foam rheology or foam collapse. T1 dynamics depends mainly on the surfactants used to generate the foam, and several models taking into account surface viscosity and/or elasticity have been proposed. By performing experiments in a cubic assembly of films, we go a step forward in this global analysis and investigate experimentally the mechanism of formation of the new film. In particular, the flow velocity field is probed by particle tracking and the film thickness is measured by light absorption and interferometric measurements. Two limit behaviours for the film are reported: it may (i) undergo an homogeneous extension, or (ii) resist elongation and remain at rest, new film being created from liquid exchange with connecting meniscus. Both T1 dynamics and film thickness are shown to depend on the competition between these two behaviours. Interestingly, their balance is set by the surfactant solution used, but it is also shown to vary during a single T1 relaxation process.

Understanding the dynamics of a droplet pushed by an external fluid in a confined geometry calls for the identification of all the dissipation mechanisms at play in the lubrication film between droplet and cell wall. Experimentally, reflection interference contrast microscopy has proven an efficient tool to measure the thickness of such lubrication films for microfluidic droplets, with a precision of a few nanometres (Huerre et al., Lab on a Chip, vol. 16 (5), 2016, pp. 911–916). The present work takes advantage of the high accuracy of this technique to chart quantitatively the lubrication film between oil droplets and the glass wall of a microfluidic chamber. We find that the lubrication films exhibit a complex three-dimensional shape, which we are able to rationalize using a hydrodynamical model in the lubrication approximation. We show that the complete topography cannot be recovered using a single model boundary condition along the whole interface. Rather, surface tension gradients are negligible at the front of the droplet, whereas they significantly modify the film profile at the rear, where surfactant accumulation induces local thickening of the lubrication film. The presence of ravines on the sides of the droplet is due to three-dimensional effects which can be qualitatively reproduced numerically. To our knowledge, this is the first experimental investigation of such local effects on travelling droplets.