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Robust surfaces capable of reducing flow drag, controlling heat and mass transfer, and resisting fouling in fluid flows are important for various applications. In this context, textured surfaces impregnated with a liquid lubricant show promise due to their ability to sustain a liquid-liquid layer that induces slippage. However, theoretical and numerical studies suggest that the slippage can be compromised by surfactants in the overlying fluid, which contaminate the liquid-liquid interface and generate Marangoni stresses. In this study, we use Doppler-optical coherence tomography, an interferometric imaging technique, combined with numerical simulations to investigate how surfactants influence the slip length of lubricant-infused surfaces with longitudinal grooves in a laminar flow. We introduce surfactants by adding tracer particles (milk) to the working fluid (water). Local measurements of slip length at the liquid-liquid interface are significantly smaller than theoretical predictions for clean interfaces (Sch\"onecker & Hardt 2013). In contrast, measurements are in good agreement with numerical simulations of fully immobilized interfaces, indicating that milk particles adsorbed at the interface are responsible for the reduction in slippage. This work provides the first experimental evidence that liquid-liquid interfaces within textured surfaces can become immobilized in the presence of surfactants and flow., Comment: 28 pages, 18 figures

The thickness of freshly made soap films is usually in the micron range, and interference colors make thickness fluctuations easily visible. Circular patterns of constant thickness are commonly observed, either a thin film disc in a thicker film or the reverse. In this Letter, we evidence the line tension at the origin of these circular patterns. Using a well controlled soap film preparation, we produce a piece of thin film surrounded by a thicker film. The thickness profile, measured with a spectral camera, leads to a line tension of the order of 0.1 nN which drives the relaxation of the thin film shape, initially very elongated, toward a circular shape.A balance between line tension and air friction leads to a quantitative prediction of the relaxation process. Such a line tension is expected to play a role in the production of marginal regeneration patches, involved in soap film drainage and stability., Comment: Physical Review Letters, In press

The presence of liquid water in frozen media impacts the strength of soils, the growth of frost heave, plant life and microbial activities, or the durability of infrastructures in cold regions. If the effect of confinement on freezing is well known, water is never pure and solutes depressing the freezing point are naturally found. Moreover, the combination of confinement and solute is poorly understood. We imaged the freezing dynamics of water in a model porous medium with various salt (KCl) concentrations. We showed that the freezing front, initially heterogeneous due to confinement, drives salt enrichment in the remaining liquid, further depressing its freezing point. Confinement and solute have a synergistic effect that results in much larger mushy layers and greater freezing point depression. These results should help understand the distribution of water in frozen porous media, solute precipitation and redistribution in soils, and cryo-tolerance of construction materials and organisms., Comment: 10 pages, 2 figures, 23 references