Polyhydric alcohols under high pressure: comparative ultrasonic study of elastic properties

We carried out an experimental ultrasonic study of polyhydric alcohols with the general chemical formula C_nH_n+2(OH)_n with an increasing number of OH groups: glycerol (n=3), erythritol (n=4), xylitol (n=5), sorbitol (n=6). The baric and temperature dependences of the elastic characteristics of these substances in the crystalline and glassy states were studied both under isothermal compression up to 1 GPa and during the isobaric heating of 77-295 K. For glycerol, glasses were obtained at different cooling rates, glass-liquid transitions were studied at different pressures. All the studied glasses have lower elastic moduli than the same substances in the crystalline state at the same pressure-temperature conditions. We obtained a cascade of glass-supercooled liquid-crystal transitions during heating of glassy erythritol. In the series of substances with n=3,4,5 the bulk moduli show a tendency to decrease with increasing n. However, sorbitol (n=6) unexpectedly has the highest elastic moduli among the studied substances in both the glassy and crystalline states. The studied glassformers show a general tendency to increase the glass transition temperature T_g and the fragility coefficient m with increasing n.