Self-Sustained Freeze–Sublime Oscillations at a Micrometer Liquid–Vacuum Interface

Liquids exposed to vacuum through micrometer-scale apertures undergo rapid nonequilibrium phase evolution driven by flash evaporation, evaporative cooling, and transient solidification. Here we investigate the self-sustained freeze-sublime oscillatory behavior of pure acetone and acetone-water mixtures effusing through a 3 μm aperture into vacuum using single-photon ionization time-of-flight mass spectrometry. Periodic vapor emission events are observed on time scales of tens of seconds and are attributed to a recurring freeze-sublime cycle in which evaporative cooling induces transient solidification within the microchannel, temporarily suppressing flow until sublimation reopens the aperture. The temporal decay of acetone emission is analyzed using a Hertz-Knudsen evaporation framework, allowing estimation of the transient temperature profile and the characteristic dimensions of the frozen region. Addition of water substantially modifies the oscillatory dynamics, reducing the cycle frequency and producing delayed water emission relative to acetone, consistent with previously observed compositional segregation within the frozen plug. Heat-transfer simulations support the hypothesis of the formation of highly localized cooling zones near the liquid-vacuum interface capable of initiating transient solidification. These results establish micron-scale liquid-vacuum interfaces as nonequilibrium systems governed by evaporation, heat transport, and phase transitions, with implications for microfluidics, vacuum-interface chemistry, and outgassing processes in astrophysical environments.