Foam stability plays a critical role in a wide range of industrial and scientific applications. In this study, an innovative method is presented for assessing foam stability through electrical conductivity measurements of liquid films formed within a controlled experimental setup. A modified horizontal glass capillary system with vertically aligned copper electrodes was developed, allowing the continuous monitoring of film drainage and rupture behavior under precise humidity (92% RH) and temperature (30 °C). Experiments were conducted using various concentrations of sodium dodecyl sulfate and Ethylan 1005, with and without NaCl addition. The results demonstrate that film stability increases with higher surfactant concentrations up to a point, beyond which the addition of salt can have either stabilizing or destabilizing effects depending on whether concentration levels are below or above the Critical Micelle Concentration (CMC). At sub-CMC levels, NaCl enhanced film stability by promoting surfactant adsorption and reducing electrostatic repulsion. Conversely, in super-CMC conditions, NaCl led to film destabilization, likely due to changes in interfacial structure and micellar behavior. This approach provides a simple, sensitive, and reproducible technique to quantitatively characterize foam film stability, offering key mechanistic insights and practical guidance for the formulation and optimization of foaming systems across diverse applications.

Binary surfactant formulations can modify thin-film stability through non-additive changes in adsorption, interfacial mobility, and surface rheology. This study extends an electrical liquid-bridge method previously developed for single surfactants to binary systems containing sodium dodecyl sulfate (SDS), benzalkonium chloride (BAC), Ethylan 1005, sodium oleate, and polypropylene glycol 600 (PPG 600). Sixteen formulations were examined at fixed drainage rates of 10 and 20 µL h⁻¹ using normalized apparent-conductance measurements synchronized with optical recording and TechDig contour reconstruction. Fifteen formulations formed measurable films at both rates, whereas 250 ppm SDS + 500 ppm sodium oleate (nominal mass–concentration ratio 1:2) failed by neck rupture before film formation. Binary mixtures either prolonged film lifetime relative to matched single-component references or enabled film formation where the reference was non-film-forming. Optical measurements independently supported the electrical ranking: longer-lived films generally reached smaller terminal neck diameters. The longest-lived formulation, 3000 ppm SDS + 500 ppm sodium oleate, also reached the smallest terminal neck. Pump-based mass balance and terminal bubble deformation further supported greater liquid removal and axial stretching before rupture. The combined electrical–optical approach provides a reproducible comparative framework for composition-dependent thin-film stabilization.