Low-temperature supercooled phase of alpha-cyclodextrin : 4-methylpyridine : water mixture

A mixture made of alpha-cyclodextrin, 4-methylpyridine and water was recently reported to undergo an inverse melting/freezing phenomenon. The physical origin of this counterintuitive process is still a debated issue; nevertheless, the interplay of structural and dynamic features seems a key point in solving the apparent thermodynamic paradox. We investigated the dynamics of this mixture in a wide range of temperature, concentration and wavevector by time-resolved transient grating spectroscopy. We found that in the lower temperature region of the phase diagram the mixture shows clear evidence of a viscoelastic effect and a slowing-down phenomenon. These dynamic features suggest the presence of a glass transition at low temperature.