Interaction forces between bubbles in the presence of novel responsive peptide surfactants.

Reversibly switchable surfactants are increasingly important for controlling foam stability in many industrial applications because they can be recycled as foaming and antifoaming agents. Novel stimuli responsive peptide surfactants have been previously studied to classify the molecular conformation at the air-water interface before and after switching. In this study, Atomic Force Microscopy (AFM) was used to correlate the peptide conformation to directly measured changes in colloidal interaction forces between immobilized air bubbles before and after switching. The surface tension values extracted from the AFM force measurements were compared to macroscopic pendant drop measurements to help elucidate the importance of desorption in the switching mechanisms for some of the peptides. Results were compared to previous studies of macroscopic foam-column stability using these peptides. Differences in foam stability and the AFM force measurements were apparent, highlighting variations in directly measured equilibrium colloidal interactions to macroscopic bulk behavior. These results help elucidate the connection between the switching mechanism of novel stimuli responsive peptide surfactants and their effect on colloidal scale interactions between bubbles.