Broadband dielectric spectroscopy in neat and binary molecular glass formers

Meer over het boek

Neat and binary molecular glass formers are examined using broadband dielectric spectroscopy to systematically understand the molecular slowing down characteristic of the glass transition. By integrating frequency and time domain techniques, a dynamic range from 10⁻6 Hz to 10 Hz is achieved. The study highlights that different types of secondary relaxations can emerge during supercooling. In simple glass formers, these secondary processes often have an intermolecular origin, and in mixtures of small and large molecules, altering the concentration of constituents can systematically change the secondary relaxations. This helps clarify the relationship between various secondary processes. Glass-forming substances typically exhibit non-exponential decay of orientational correlations, resulting in broadened dielectric loss spectra compared to simple Debye-like relaxation. This effect is especially notable in binary glass formers, and one objective is to provide a suitable tool for line shape analysis of relaxation spectra in both neat and binary systems. Additionally, the nature of spectral broadening is explored through non-resonant dielectric hole burning, which differentiates between heterogeneous and homogeneous dynamics. The findings indicate that dynamic heterogeneities are particularly pronounced in binary glass formers, and the effects of dielectric hole burning in both neat and binary systems align well with a model of sel