1 research outputs found
Effects of Fluid Confinement and Temperature in Supported Acetophenone Films
Solid–liquid
phase transitions are thought to be well understood
in bulk phases of matter, but in thin films or interfacial volumes,
melting and freezing transitions can exhibit significant departures
from expected behaviors. Here, we show multiple solid–liquid
phase transitions in thin films (50–500 nm) of the molecular
fluid acetophenone. Transitions are driven by both geometric confinement
and temperature, as characterized by spectroscopy. Fluid film confinement
is controlled by systematic variation of the supported film thicknesses,
and the same films are passed through cooling–heating cycles
to generate amorphous or crystalline films with distinctly different
molecular environments. Specifically, multiple temperature cycles
reveal a distinct conditioning dependence, wherein phase transitions
may or may not exhibit significant changes in the infrared absorption
profile over the temperature cycle, indicating distinct crystalline
and liquid-like phases. Significant effects of supercooling are also
observed as a result of the highly confined nature of the thin-film
sampling geometry. Interestingly, the spectral profiles recorded as
a function of film temperature show clear evidence of molecular reordering
phase transitions, which is similar to observations in variable thickness
films held at constant temperature. The changes in spectral absorption
profiles confirm the confinement-induced crystalline ordering and
provide evidence that molecular confinement effects can extend beyond
100 nm from a surface, which is much larger than conventionally accepted
“interfacial” volumes. Ultimately, the extended crystalline
ordering within liquid films could offer important new avenues to
tune the physical properties of designer interfaces