Solutions of surfactant oligomers: a model system for tuning foam stability by the surfactant structure

We report experiments on aqueous foams made of solutions of oligomers of cationic surfactants. The degree of oligomerization is varied up to 4, and two spacer lengths are used. We have studied both the interfacial dilational and shear rheology, the single thin film properties, the foamability of the solutions, as well as the aging and the mechanical properties of the 3D foams. We have found clear differences between the oligomeric systems at all length scales. We then discuss the correlations between the properties at the different length scales and see how the macroscopic features depend on the molecular structure. This work first allows us to determine the relevance of each measurement; in that respect, it stresses the important role of the timescales, and the need to monitor the liquid fraction and bubble size in order to perform correct comparisons. Secondly, this work provides information on how one could optimize foaming properties with oligomers, and the balance between the degree of oligomerization and spacer length.