We have studied interfacial properties
of fully condensed octakis[{2-(3,4-epoxycyclohexyl)etyl}dimethylsilyloxy]octasilsesquioxane
(OE-POSS). The surface pressure–area isotherm obtained in a
Langmuir trough together with Brewster angle microscopy indicated
formation of a stable, homogeneous liquid-like monolayer. For low
molecular areas, the monolayer undergoes a stepwise collapse showing
unusual multilayer morphology. A collapse mechanism is proposed to
be a consequence of progressive decrease in the distance between silicon–oxygen
cages after reorganization of side groups. Hysteresis experiment showed
incomplete respreading of small aggregates and successive decrease
in molecular areas. Relaxation measurements indicated a slight impact
of desorption and molecular rearrangements on the monolayer stability.
Interfacial rheology was investigated for compressional deformation
of the air/water interface. Both components of surface dilational
modulus (elastic, E′, and viscous, E″) were determined by the oscillating barriers method.
With increasing frequency, E′ decreased while E″ increased almost linearly. The loss angle tangent
indicated elastic response of the monolayer in the range of low deformation
rates and viscous behavior when subjected to fast deformation. The
rheological behavior of the monolayer is also strongly affected by
the collapse mechanism that begins at 20 mN/m.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.