Glass transition and structural relaxation of intermediate liquids by MDSC and dielectric spectroscopy

The behavior of liquid–glass transition and structural relaxation of several intermediate glass forming liquids was investigated by means of MDSC and dielectric measurements. The MDSC scan for the monomer and its oligomers of propylene glycol and propylene glycol monomethyl ether shows a step-like increase in a real part of heat capacity and a peak in an imaginary part of heat capacity. The glass transition temperature is defined as a peak point of an imaginary part of heat capacity. The calorimetric relaxation behavior was in agreement with the dielectric relaxation behavior. This fact indicates that the rotational behavior of molecules at a liquid state also plays a dominant role in a glass transition phenomenon. The glass transition temperature is controlled by both the molecular weight and the number of hydroxyl end groups. The change of glass transition temperature of several alcohols was discussed in terms of two order parameter model, using density and bond order parameters. The packing effect by alkyl group in alcohol influences the density which is controlled by the isotropic interaction among molecules. The presence of hydroxyl group controls mainly the anisotropic bond order parameter. The frustration between these two order parameters datermines the physical properties of glass-forming liquid through a glass transition.