Common Origin of Dynamics Heterogeneity and Cooperatively Rearranging Region in Polymer Melts

If some supercooled liquids are cooled further, they freeze into a specific medium state with both properties of liquid-like structure and solid-like hardness, so-called “glass.” The fact that dynamics freeze drastically when there is only a slight change in static structure remains a mystery in solid-state physics. Recently, it has been reported that when a particular kind of glass-forming liquids with two order parameters are cooled rapidly, local crystalline orders with extremely slow dynamics start to emerge when approaching glass transition temperature. This result suggests a concept of “frustration to crystallization” as a physical picture of glass transition. On the other hand, although Adam–Gibbs theory has predicted the existence of cooperatively rearranging region (CRR) as the origin of extreme slowdown in dynamics, CRR is still no more than a hypothetical subsistent to explain the slow dynamics of glass transition. In this study, we found for the first time, local-bond orientational orders, “LBOOs,” which characterize glass transition in polymer melts, one of the most representative glass-forming liquids. Furthermore, we confirmed that monomers composed of LBOOs were concertedly vibrating and indicated that LBOOs can be identified as CRR. In other words, we were able to prove that the LBOOs we have discovered were consistent with both the physical picture of frustration to crystallization and Adam–Gibbs’ theory.