Portal de Periódicos da CAPES

Dielectric Relaxation and Calorimetric Measurements of Glass Transition in the Glass-Forming Dyhydroxyl Alcohols

1998; Physical Society of Japan; Volume: 67; Issue: 12 Linguagem: Inglês

10.1143/jpsj.67.4131

1347-4073

In‐Sung Park, Kenichi Saruta, Seiji Kojima,

Liquid Crystal Research Advancements

In order to study the molecular weight dependence of the α-relaxation and glass transitions of intermediate glass-forming materials, the dielectric and thermal properties have been investigated in both liquid and supercooled liquid states. By means of modulated DSC at 10 mHz and broadband dielectric spectroscopy in the frequency range from 10 mHz to 10 GHz, propylene glycol (PG) and its five oligomers (poly propylene glycol, PPG), which have the similar chemical structure but different molecular weights 76–4000 g/mol, were studied paying attention to their fragility and cooperativity. The fragility of PG and PPGs from the dielectric and thermal measurements was analyzed and compared using both the intermolecular cooperativity model and the Adam-Gibbs model. The Vogel-Fulcher energy and minimum configurational entropy were evaluated for PG and PPGs using the comparison method. Their values were related to the density of -OH end group and its intermolecular hydrogen bonding. The strength parameter decreased with increasing molecular weight indicating that PG monomer liquid is stronger than PPG liquids. The domain size at T g , which was introduced by the Matsuoka's cooperativity model, was about 2 to 5 for PG and PPGs, increasing with molecular weight. The increase of the domain size in the vicinity of T g was shown to be related to the larger non-exponentiality.