Portal de Periódicos da CAPES

Molecular Dynamics in Binary Organic Glass Formers

1999; American Chemical Society; Volume: 103; Issue: 20 Linguagem: Inglês

10.1021/jp983754x

1520-6106

Th. Blochowicz, C. Karle, A. Kudlik, P. Medick, I. Roggatz, M. Vogel, C. Tschirwitz, Jan Wolber, Jürgen Senker, E. A. Rössler,

Thermodynamic properties of mixtures

We investigated binary low-molecular-weight glass formers as model systems for mixtures of small and large molecules. Tricresyl phosphate (TCP) in oligomeric styrenes (OS), benzene in OS and polystyrene (PS), and benzene in TCP were studied by applying dielectric spectroscopy as well as 1H, 2H, and 31P NMR spectroscopy. Temperatures above and below the glass-transition temperature (TG) are covered. The dielectric loss of the small component appears broader the higher the molecular ratio M/m is, and the lower the TCP concentration and the lower the temperature are chosen. Close to TG, extremely broad distributions of correlation times G(log τ) result, which are similar to those reported in the cases of polymer−plasticizer systems, although for our systems the motional heterogeneities are already established at similar M and m. By applying 1H and 2H (1D and 2D) NMR on benzene in OS and PS, we can demonstrate that the large molecules basically behave as in neat glass formers. However, the small molecules exhibit an isotropic reorientation also well below TG, and the dynamics is rather characterized by a random jump process than by rotational diffusion, the latter being found in neat systems. Furthermore, we can prove that within G(log τ), exchange processes take place, even below TG, which essentially occur on the same time scale as reorientation.