title: Phase transitions of amorphous solid acetone in confined geometry investigated by reflection absorption infrared spectroscopy.
abstract: We investigated the phase transformations of amorphous solid acetone under confined geometry by preparing acetone films trapped in amorphous solid water (ASW) or CCl4. Reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) were used to monitor the phase changes of the acetone sample with increasing temperature. An acetone film trapped in ASW shows an abrupt change in the RAIRS features of the acetone vibrational bands during heating from 80 to 100 K, which indicates the transformation of amorphous solid acetone to a molecularly aligned crystalline phase. Further heating of the sample to 140 K produces an isotropic solid phase, and eventually a fluid phase near 157 K, at which the acetone sample is probably trapped in a pressurized, superheated condition inside the ASW matrix. Inside a CCl4 matrix, amorphous solid acetone crystallizes into a different, isotropic structure at ca. 90 K. We propose that the molecularly aligned crystalline phase formed in ASW is created by heterogeneous nucleation at the acetone-water interface, with resultant crystal growth, whereas the isotropic crystalline phase in CCl4 is formed by homogeneous crystal growth starting from the bulk region of the acetone sample.
authors.affiliation: Department of Chemistry, Seoul National University , 1 Gwanak-ro, Seoul 151-747, South Korea.
authors.forename: Sunghwan
authors.initials: S
authors.lastname: Shin
authors.forename: Hani
authors.initials: H
authors.lastname: Kang
authors.forename: Jun Soo
authors.initials: JS
authors.lastname: Kim
authors.forename: Heon
authors.initials: H
authors.lastname: Kang
mesh_terms: D000096:Acetone / Q000737:chemistry*; D002251:Carbon Tetrachloride / Q000737:chemistry; D044367:Phase Transition; D013055:Spectrophotometry, Infrared; D013696:Temperature; D014732:Vibration; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D000096:Acetone; D002251:Carbon Tetrachloride