Glassy feature in melts of 3-dimensional architectured polymer blends

Abstract

3-dimensional architectured polymers, for example, giant molecules, present distinct dynamics from chain-like polymers and are coarse-grained as soft-clusters. There is a critical number of beads, above which their melts cannot relax under thermal energy and become cooperative glass. To reveal the role of dispersity, we study the dynamics of binary blends of giant molecules with the same glass transition temperature by rheological experiments and by molecular dynamics simulations. The large component of the blend, OPOSS24 or 141335, contains more beads than the critical number and forms cooperative glass, while the small component contains less beads than the critical number. The gradual change of volume fraction allows us to fine-adjust the average number of beads. An abrupt slowdown happens only if the volume fraction of the large component reaches 80%. Both experimental and simulated data can be described by a Vogel–Fulcher–Tammann-like equation against volume fractions with only one fitting parameter. The divergent relaxation times can also be rewritten as a function of the average number of beads. Such abrupt dynamic slowdown has to be induced by the glass-like cooperative dynamics. The cooperative glass state may only be reached when the majority of giant molecules or generally speaking, soft-clusters, are large enough. If we regard binary blends of soft-clusters as large and small cooperative rearranging regions, this may provide a direct approach to glass problems and may shed light on our understanding.