We investigate the effect of a high concentration (32.5 normal g normal upper L Superscript negative 1 g L − 1 gL−1 ) of sodium chloride (NaCl) on tetradecyltrimethylammonium bromide vertical soap films, also called foam films, pulled out of a bath under controlled humidity conditions. We observe that the film lifetime increases with relative humidity, both in the presence and absence of salt. At any given humidity, the presence of NaCl systematically enhances film stability. Our film thickness measurements show that the thinning dynamics with or without salt is nearly identical down to 100 nm. Down to that thickness, the effect of evaporation can be rationalised by a constant evaporation rate, which becomes non-negligible compared with the drainage rate at film thicknesses below 400 nm. The main effect of salt is the stabilisation of a Newton black film at a thickness of approximately 5 nm, whereas in the absence of salt, the film ruptures upon reaching a critical thickness of approximately 10 nm.

We present a practical white-light interferometric method, supported by an open-source Python library optifik for automated spectrum-to-thickness deduction, enabling foam film measurements down to a few nanometers. We describe three typical spectral scenarii encountered in this method: spectra exhibiting numerous interference fringes, spectra with a moderate number of peaks, and spectra with only a few identifiable features, providing illustrative examples for each case. We also discuss the main limitations of the technique, including spectral range constraints, the necessity of knowing the refractive index, and the influence of spectral resolution and signal quality. Finally, we demonstrate the application of the method in a time-resolved study of a TTAB (tetradecyltrimethylammonium bromide) foam film undergoing elongation and thinning. This method can be adapted to measure any thin non-opaque layer.

Understanding the stability of foam films and foams remains a challenge, despite the considerable efforts provided by the scientific community to refine their physical descriptions. This persistent difficulty underscores the interplay of various complex factors. Recently, the role of evaporation has attracted attention for its dual impact: it can either enhance stability or accelerate bursting. To depict a comprehensive overview on soapy objects, we propose first a short description on the evaporation of drops to present some key results on the evaporation-induced cooling and the consequences on the internal flows generated by Marangoni effects. Then, we review the literature on foam films and foams, examining three distinct systems: pure liquids, nonvolatile, and volatile surface active molecules. We show that evaporation of foam films and foams can lead to significant variations of temperature. In conclusion, we identify a series of open questions and suggest potential research pathways to address these challenges.

The crystallisation that occurs when a drop is placed in contact with a cold surface is a particularly challenging phenomenon to capture experimentally and describe theoretically. The situation of a liquid-liquid interface, where crystals appear on a mobile interface is scarcely studied although it provides a defect-free interface. In this paper, we quantify the dynamics of crystals appearing upon the impact of a drop on a cool liquid bath. We rationalize our observations with a model considering that crystals appear at a constant rate depending on the thermal shock on the expanding interface. This model provides dimensionless curves on the number and the surface area of crystals that we compare to our experimental measurements.

Acquiring a comprehensive understanding of the interplay between foam friction and surface roughness is essential for achieving precise control over their flow dynamics. In particular, a major challenge is to reduce friction, which can be achieved with rough surfaces in the situation where a liquid infuses the asperities. In this study, we propose to explore self-infused surfaces. We first present simple observations to demonstrate the effectiveness of our surface design by recording the motion of a foam puddle on a smooth surface and self-slippery liquid-infused porous surfaces. To quantify friction reduction, we conduct stress measurements on surfaces moved at a constant velocity. Finally, we interpret the variation of the friction force with the velocity by a model considering an effective slip length of the surface. This research paves the way for a unique approach to mitigate dissipation in liquid foam flows, holding significant implications for reducing energy consumption in conveying foams for industrial processes and various end-use applications.