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

Abstract

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.