Dynamics in glass-forming mixtures: Comparison of behavior of polymeric and non-polymeric components

Recent experiments have shown that the segmental dynamics of dilute polymer chains in glass-forming matrices are substantially different than the dynamics of the host. In contrast, we show here that the dynamics of dilute low molecular weight species (tetracene and rubrene) are very similar to the dynamics of the host matrix. This is consistent with the view that self-concentration is a dominant factor in determining the dynamics of polymer chains in glass-forming mixtures; as a polymeric effect, self-concentration should be negligible for low molecular weight species. In addition, we show that self-concentration may play an important role in understanding segmental dynamics in concentrated polymer solutions.