INFORM March 2025

inform March 2025, Vol. 36 (3) • 35

Determining interfacial tension and critical micelle concentrations of surfactants from atomistic molecular simulations Cárdenas, H., et al. , Journal of Colloid and Interface Science , 674, 1071, 2024. https://doi.org/10.1016/j.jcis.2024.07.002 Hypothesis Atomicly-detailed models of surfactants provide quantitative information on the molecular interactions and spatial distributions at fluid interfaces. Hence, it should be possible to extract from this information, macroscopical thermophysical properties such as interfacial tension, critical micelle concentrations and the relationship between these properties and the bulk fluid surfactant concentrations. Simulations and Experiments Molecular-scale interfacial systems containing n- do decyl β -glucoside (APG 12 ) are simulated using classical molecu lar dynamics. The bulk phases and the corresponding interfacial regions are all explicitly detailed using an all-atom force field (PCFF+). During the simulation, the behaviour of the interface is analyzed geometrically to obtain an approximated value of the crit ical micelle concentration (CMC) in terms of the surfactant area number density and the interfacial tension is assessed through the analysis of the forces amongst molecules. New experimental determinations are reported for the sur face tension of APG 12 at the water/air and at the water/ n -decane We showcase the application of a thermodynamic framework that inter-relates interfacial tensions, surface densities, CMCs and bulk surfactant concentrations, which allows the in silico quantitative prediction of interfacial tension isotherms. Oppositely charged surfactants and nanoparticles at the air-water interface: Influence of surfactant to nanoparticle ratio Eftekhari, M., et al. , Journal of Colloid and Interface Science , 653, Part B, 1388, 2024. https://doi.org/10.1016/j.jcis.2023.09.038 Hypothesis The interactions between oppositely charged nanoparti cles and surfactants can significantly influence the interfacial properties of the system. Traditionally, in the study of such systems, the nanoparticle concentration is varied while the surfactant concentration is kept constant, or vice versa. However, we believe that a defined variation of both components› concentration is necessary to accurately assess their effects on the interfacial properties of the system. We argue that the effect of nanoparticle surfactant complexes can only be properly evaluated by keeping the surfactant to nanoparticle ratio constant. interfaces. Findings

various laboratory tests. In particular, two regimes of foam gener ation are considered: at low surfactant concentrations where the coalescence between the bubbles plays a crucial role, and a high surfactant concentration range where the hydrodynamic condi tions are much more important for the final outcome of foam ing. The review discusses the role of surfactant concentration, dynamic surface coverage, and surface forces acting between film surfaces for the foam generated in the surfactant-poor regime. Additionally, the interplay between the hydrodynamic condi tions and the viscosity of the formed foams in the surfactant-rich regime is also discussed. An experimental study of foam-oil interactions for nonionic-based binary surfactant systems under high salinity conditions Bello, A., et al. , Scientific Reports , 14, 12208, 2024. https://www.nature.com/articles/s41598-024-62610-1 A key factor affecting foam stability is the interaction of foam with oil in the reservoir. This work investigates how dif ferent types of oil influence the stability of foams generated with binary surfactant systems under a high salinity condition. Foam was generated with binary surfactant systems, one com posed of a zwitterionic and a nonionic surfactant, and the other composed of an anionic and a nonionic surfactant. Our results showed that the binary surfactant foams investigated are more tolerant under high salinity conditions and in the presence of oil. This was visually observed in our microscopic analysis and was further attributed to an increase in apparent viscosity achieved with binary surfactant systems, compared to single surfactant foams. To understand the influence of oil on foam stability, we performed a mechanistic study to investigate how these oils interact with foams generated with binary surfactants, focusing on their applicability under high salinity conditions. The generation and stability of foam are linked to the ability of the surfactant system to solubilize oil molecules. Oil droplets that solubilize in the micelles appear to destabilize the foam. However, oils with higher molecular weights are too large to be solubilized in the micelles, hence the molecules will have less ability to be transported out of the foam, so oil seems to stabi lize the foam. Finally, we conducted a multivariate analysis to identify the parameters that influenced foam stability in differ ent oil types, using the experimental data from our work. The results showed that the oil molecular weight, interfacial tension between the foaming liquid and the oil, and the spreading coef ficient are the most important variables for explaining the varia tion in the data. By performing a partial least square regression, a linear model was developed based on these most important variables, which can be used to predict foam stability for subse quent experiments under the same conditions as our work.