Anomalous generation and extinction of crystal nuclei in nonequilibrium supercooled liquido-benzylphenol

Crystal-nucleation phenomena of supercooled liquid o-benzylphenol are studied by differential scanning calorimetry (DSC). While crystallization proceeds with crystal nucleation and growth processes, only the latter process can be observed calorimetrically. Whether there exist crystal nuclei in the supercooled liquid or not was therefore judged by whether crystal growth does or does not proceed in the course of subsequent DSC measurement. The liquid sample was cooled rapidly at 200 K min^-1 from above fusion temperature down to each desired aging temperature (Tₐ) below the {α}-glass transition temperature (T_gα=223K), and annealed there for different periods (tₐ) for enhancement of crystal nucleation, if any. The sample was then heated at 200 K min^-1 up to 213 K a little below T_gα, and measured at 10 K min^-1 to examine if the crystallization/fusion behaviors appear. It was discovered that (1) crystal nuclei are generated and increased in the number during the aging at 143K<~Tₐ<~213K; (2) they are generated immediately after the rapid cooling, then extinguished and again generated at 128K<~Tₐ<~133K; and (3) they are generated and decreased in the number but some survive at Tₐ<~123K. The generation and extinction of the crystal nuclei in a nonequilibrium state much below the T_gα are discussed based on the ordered-clusters aggregation model for a supercooled-liquid structure.