Crystal melting processes of propylene carbonate and 1,3-propanediol investigated by the reed-vibration mechanical spectroscopy for liquids

The melting of crystals is one of the most common and general phase transition phenomena. However, the mechanism of crystal melting is not well understood, and more experimental measurements and explorations are still needed. The mechanical spectra of propylene carbonate and 1,3-propanediol during the crystal melting processes are measured by the reed vibration mechanical spectroscopy for liquids (RMS-L) for the first time. The experimental results show that as the temperature increases, the real part of the complex Young modulus first decreases slowly, and then quickly drops to zero; meanwhile, its imaginary part increases slowly at first, then goes up and drops quickly to zero, showing a peak of internal friction. Preliminary analyses indicate that both the real and imaginary parts can present some characteristics of the melting process, such as the transition from the disconnected liquid regions to the connected liquid regions, that from the connected crystal regions to the disconnected crystal regions, and so on. In addition, the results show that the melting rate per unit volume of crystalline phase versus temperature satisfies the Arrhenius relation at the initial stage of melting, and deviates from this relation as the temperature increases to a certain value. Therefore, the RMS-L will provide an effective supplement for the further study of melting.