1 research outputs found
Semifluorinated Alkanes at the Air–Water Interface: Tailoring Structure and Rheology at the Molecular Scale
Semifluorinated alkanes form monolayers
with interesting properties
at the air–water interface due to their pronounced amphi-solvophobic
nature and the stiffness of the fluorocarbons. In the present work,
using a combination of structural and dynamic probes, we investigated
how small molecular changes can be used to control the properties
of such an interface, in particular its organization, rheology, and
reversibility during compression–expansion cycles. Starting
from a reference system perfluorÂ(dodecyl)Âdodecane, we first retained
the linear structure but changed the linkage groups between the alkyl
chains and the fluorocarbons, by introducing either a phenyl group
or two oxygens. Next, the molecular structure was changed from linear
to branched, with four side chains (two fluorocarbons and two hydrocarbons)
connected to extended aromatic cores. Neutron reflectivity at the
air–water interface and scanning force microscopy on deposited
films show how the changes in the molecular structure affect molecular
arrangement relative to the interface. Rheological and compression–expansion
measurements demonstrate the significant consequences of these changes
in molecular structure and interactions on the interfacial properties.
Remarkably, even with these simple molecules, a wide range of surface
rheological behaviors can be engineered, from viscous over viscoelastic
to brittle solids, for very similar values of the surface pressure