Hideyuki Nakayama

Crystallization and glass-transition phenomena were studied for amorphous chlorobenzene (CB)/toluene (TL) binary systems as the function of composition. Samples were prepared by vapor-deposition onto cold substrates, and their structural changes due to temperature elevation were monitored with Raman scattering and light transmission. It was found that the crystallization temperature (T-c) of CB-rich amorphous samples increases as the TL concentration is increased. This is similar to the linear dependence of glass-transition temperatures (T-g) of many organic compounds on the concentration of additive. Also found was that T-c of TL-rich supercooled-liquids decrease as the CB concentration is increased. Issues related to the two kinds of T-c are discussed briefly.

Crystallization and glass-transition phenomena were studied for amorphous chlorobenzene (CB)/toluene (TL) binary systems as the function of composition. Samples were prepared by vapor-deposition onto cold substrates, and their structural changes due to temperature elevation were monitored with Raman scattering and light transmission. It was found that the crystallization temperature (Tc) of CB-rich amorphous samples increases as the TL concentration is increased. This is similar to the linear dependence of glass-transition temperatures (Tg) of many organic compounds on the concentration of additive. Also found was that Tc of TL-rich supercooled-liquids decrease as the CB concentration is increased. Issues related to the two kinds of Tc are discussed briefly.

Light transmission through amorphous chlorobenzene was studied during the vacuum deposition of the vapor onto cold substrates. It was found that samples prepared at 78 K were transparent, but those prepared at 15 K were slightly opaque. Raman and X-ray studies indicated that both kinds of samples were amorphous, but they showed different behavior against annealing. The transparent samples needed some induction period to start crystallization when the temperature was raised for annealing, while the slightly opaque samples underwent crystallization by annealing almost without any induction period. Samples prepared at very-low temperatures are considered to incorporate density inhomogeneity, and the resultant free space around molecular aggregates may allow the samples to start crystallization easily.

Light transmission through amorphous chlorobenzene was studied during the vacuum deposition of the vapor onto cold substrates. It was found that samples prepared at 78 K were transparent, but those prepared at 15 K were slightly opaque. Raman and X-ray studies indicated that both kinds of samples were amorphous, but they showed different behavior against annealing. The transparent samples needed some induction period to start crystallization when the temperature was raised for annealing, while the slightly opaque samples underwent crystallization by annealing almost without any induction period. Samples prepared at very-low temperatures are considered to incorporate density inhomogeneity, and the resultant free space around molecular aggregates may allow the samples to start crystallization easily.

By the continuous elevation of temperature, ethylbenzene in the supercooled liquid state first turns opaque and then becomes transparent again before it finally crystallizes. These observations are possibly related to the appearance of the second amorphous state with a correlated structure that has recently been reported for triphenyl phosphite.