Viscoelasticity of semifluorinated alkanes at the air-water interface

We have studied the viscoelastic properties of semifluorinated alkanes F(CF2)(n)(CH2)(n)H (referred as FnHm) confined at the air-water interface. These specially synthesized model doubly-hydrophobic macromolecules of varying architecture reside at the air-water interface in the form of well-defined disk-like surface micelles that minimize the free energy. Pressure area isotherms performed on Langmuir monolayers of these micelles indicated two transitions: one at about 4 mN/m and a second at about 8 mN/m. In both regimes a solid-like viscoelastic response was probed. In each regime the values of both the storage and the loss surface moduli increased with surface pressure. These findings are discussed in view of recent theoretical developments and provide opportunities for manipulating surface structure and rheology of such types of complex macromolecules. Finally, the effect of architecture on this surface structure - rheology interplay has been also addressed.