Dynamic Surface Excesses of Fluorocarbon Surfactants

Abstract

Dynamic adsorption and surface tension behavior of aqueous fluoro-surfactant solutions has been investigated using a range of experimental techniques, including neutron reflection (NR). Equilibrium tensions, γeq, have been measured by drop volume tensiometry (DVT), and dynamic surface tensions, γdyn, have been determined using the nonperturbative method, surface light scattering (SLS). Dynamic conditions for NR and SLS measurements were established using an overflowing cylinder (OFC). The OFC provides a dynamic surface on the 0.1−1 s time scale and offers a large (∼50 cm2), near flat surface for interrogating interfacial properties. To exploit these techniques effectively, a fluorocarbon anionic surfactant, sodium bis(1H,1H-nonafluoropentyl)-2-sulfosuccinate (di-CF4) has been specifically selected. Molecular structure effects have been explored with the C6 analogue sodium bis(1H,1H,7H-dodecafluoro-n-heptyl) sulfosuccinate (di-HCF6). Using OFC−NR, dynamic surface excesses, Γdyn, have been measured directly...