Interactions of LiI with Thin Methanol Films during Glass–Liquid Transition and Premelting

5 years ago

Interactions of LiI with Thin Methanol Films during Glass–Liquid Transition and Premelting

Ryutaro Souda

This study investigated interaction of thin methanol films with LiI at cryogenic temperatures using time-of-flight secondary ion mass spectrometry, temperature-programmed desorption, and reflection absorption infrared spectroscopy to elucidate properties of liquid-like phases formed during the glass–liquid transition and premelting of crystallites. The LiI additives are incorporated into the film interior from both the free surface and substrate interface at temperatures higher than methanol’s glass-transition temperature of 103 K. A dilute LiI solution is formed in supercooled methanol, as revealed from invariance of the OH stretching vibration frequencies relative to those of pure methanol. The uptake of LiI in supercooled methanol is quenched after crystallization at 120 K, where film morphology changes because of the grain growth. The incorporated LiI additives diffuse into deeper positions of the crystalline film at temperatures >140 K because premelting occurs at grain boundaries. When methanol is deposited onto a solid LiI film, a concentrated LiI solution is formed transiently, as evidenced by the blue shift of the OH stretching band. A multilayer methanol film as thick as 250 monolayers is converted to the LiI solution at 140 K, indicating that the premelting layer is equilibrated with methanol crystal grains. A thinner (10 monolayers) methanol film deposited on LiI produces a concentrated solution at 120 K, indicating that smaller grains premelt immediately after crystallization.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b07389

DOI: 10.1021/acs.jpcc.7b07389