Dynamic nanostructures at the surface of rising bubbles in amphiphile solutions: Comparison of low-molecular-weight surfactants and proteins

The formation, stability, and decay of foams occur under dynamic conditions. Given their inherent complexity, an accurate description of these subprocesses necessitates an analysis of multiple factors, with a particular focus on the formation and structure of the adsorption layer. Single rising bubble techniques facilitate a deeper comprehension of the dynamics of diverse phenomena in foams, as they yield experimental data under dynamic conditions. This review examines the subtle differences in the dynamic adsorption structures of low-molecular-weight surfactants and proteins at the liquid/gas interface. These differences can significantly impact interfacial properties and potentially alter our understanding of the mechanisms behind the formation of the Dynamic Adsorption Layer (DAL). The primary techniques under consideration are local velocity profiles (LVPs) of single rising bubbles and dynamic fluid-film interferometry (DFI) of the thin liquid film formed at the collision of a bubble with a free liquid surface. We provide a summary of recent findings on the topic. Due to the limited availability of comprehensive datasets on proteins, our discussion is partially supplemented by newly obtained unpublished data. We highlight key differences in the behavior of bubbles in low-molecular-weight surfactant solutions versus protein solutions that have previously been overlooked in the literature. We explore their potential origins in the context of DAL dynamics and architecture.