Glass transition in binary systems
In binary glass former dynamic heterogeneities appear to be particularly pronounced [1,2]. Thus, e.g. the dielectric susceptibility of the smaller molecules in the mixture is characterized by a broad distribution of relaxation times and may even decouple from the slower moving molecules of the matrix. That one component of the mixture indeed contains subsets of molecules which perform reorientational dynamics on very different time scales was recently demonstrated by non-resonant dielectric hole burning, where certain molecular subsets are selectively addressed by a high voltage AC pump field . Also, the behaviour of secondary relaxations strongly depends on the composition of the system and secondary processes may e.g. be separated from the main relaxation by inserting small molecules into a slower matrix.
Our main interest focuses on how the relaxation broadening and decoupling can be understood in these systems, on how secondary relaxations appear in different experimental methods that are sensitive to reorientation, and on how all of these phenomena are related to concentration fluctuations, which are known to determine the dynamics in polymer plasticizer systems and polymer blends. To improve our understanding of the underlying physical mechanisms, we attempt e.g. to compare the dynamics of small molecules in a binary mixture (i.e. a dynamically heterogeneous system under the influence of concentration fluctuations) with molecular motion in confined geometry (i.e. a dynamically heterogeneous system without concentration fluctuations). The main experimental methods applied are dynamic light scattering, dielectric spectroscopy, differential scanning calorimetry and NMR. In the near future we plan to also apply neutron scattering and X-ray photon correlation spectroscopy.
For further information please contact Dr. T. Blochowicz
- T. Blochowicz, E. Rössler, Beta Relaxation versus High Frequency Wing in the Dielectric Spectra of a Binary Molecular Glass Former, Phys. Rev. Lett., 92 (2004), p. 679-682.
- T. Blochowicz, C. Karle, A Kudlik, S. Medick, I. Roggatz, M. Vogel, C. Tschirwitz, J. Wolber, J. Senker, E. Rössler, Molecular dynamics in binary organic glass formers, J. Phys. Chem. B, 103 (1999), p. 4032-4044.
- T. Blochowicz, E. Rössler, Non-Resonant Dielectric Hole Burning in Neat and Binary Molecular Glass Formers, J. Chem. Phys., 122 (2005), 224511.