posted on 2023-11-06, 21:05authored bySrikant
Kumar Singh, Wei Bu, Pan Sun, Matthew F. Paige
A recently reported anionic gemini surfactant, a member
of the
so-called “gemini without a linker” family, has recently
been reported to form closely packed crystalline monolayers at the
air–water interface. In this work, the impact on monolayer
properties of the compound, C18-0-C18, that
result from its mixing with a benchmark perfluorinated surfactant,
perfluorotetradecanoic acid (PF), is explored. The films exhibit nonideal
mixing, as determined by surface pressure–area (π–A)
isotherms and surface potential measurements, and phase-separation
between the two components was observed by the direct visualization
of the monolayers, and grazing-incident X-ray diffraction at the air–water
interface. The pure and mixed films follow similar trends in the order
of C18-0-C18 < PF < χPF = 0.50 mixed films for both their extent of hysteresis and their
stability at the air–water interface. Further, crystallographic
data for the mixed film emerge as a simple combination of distinct
diffraction patterns characteristic of both the individual components,
consistent with the other findings reported here and thus clarify
the intermolecular behavior of the binary mixture at the surface.