| Research Abstract |
Science of Supercooled liquids and glasses has not been developed enough because of the aspect that the arrangement of molecules is essentially disordered. The development of ordering in the molecular aggregation, however, plays an important role in their characteristic properties at low temperatures. We have proposed an "ordered-clusters aggregation model" for the structure of those systems. In this research, it was tried first to realize a two-dimensional glass and observe directly the molecular aggregation and its change, and second to discover or elucidate new phenomena based on the proposed model.
1) A scanning tunneling microscope was constructed which works at liquid nitrogen temperature. o-Terphenyl molecules deposited on a graphite surface was identified, but it has not been succeeded yet to form and observe its mono-layer glass.
2) α and β relaxation times of simple benzene-derivatives were investigated dielectrically with systematic change of the substituent groups at 1 and 3-
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positions. While the β relaxation times were rather independent of the size of substituents to within isopropyl group and the presence/absence of hydrogen-bond forming, -OH and NH_2, groups, α relaxation times depended strongly on those factors. The β relaxation strength was appreciably large in the sample cooled rapidly than slowly in the α glass transition region in advance.
3) Homogeneous-nucleation-based crystallization was found in total in seven compounds with phenyl rings, indicating that the presence of the ring is important for its observation. It was also indicated to be important for the observation that the orientation of the crystal nucleus should coincide with that of the original crystal.
4) Crystal nucleation was followed for o-benzylphenol after the liquid was cooled very rapidly from above fusion point to below the α glass transition temperature. It was found in a certain temperature region that the crystal nuclei were formed, then extinguished, and formed again after further long duration.
5) In addition to a normal liquid (L_N) phase, another amorphous (L_C) phase was confirmed to exist in triphenylphosphite. Based on the α relaxation properties of the L_N and L_C phases, it was discussed that, in general, the α molecular rearrangement process is controlled by two relatively independent factors : the size of structurally ordered cluster and the degree of the order in the cluster, and that the relaxation time is basically determined by the latter factor. Less
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