Interfacial Characteristics and Foam Stability: A Microscopic Perspective from Molecular Dynamics Simulation

Foams play a pivotal role in diverse industrial and academic applications, yet their stability, particularly in relation to surfactants, remains inadequately understood at the microscopic level. This study undertakes a comprehensive modeling of water films stabilized by 15 surfactants, spanning 4 ion types of hydrophilic groups. We conducted a systematic comparison and correlation of key interfacial characteristics at different stages of rupture. Our findings reveal that the critical film thickness and interface tension are integral in characterizing foam stabilities near equilibrium (metastable state) and near rupture (critical state), respectively. Furthermore, we observed a positive correlation between the hydrophilicity of surfactant head groups and both the thickness of Gibbs dividing surface and the orderliness of interfacial surfactant molecules. These factors are crucial in maintaining film stability in both metastable and critical states. This work presents a quantitative framework to generalize various interfacial characteristics commonly employed in describing foam stability, which is poised to enhance the data-driven methodology for surfactant selection and design.