Effects of Fluid Confinement and Temperature in Supported Acetophenone Films

Abstract

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 obser...