Dresden 2003 – wissenschaftliches Programm
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DF: Dielektrische Festkörper
DF 5: Gl
äser II (gemeinsam FV DF/DY)
DF 5.11: Vortrag
Dienstag, 25. März 2003, 17:15–17:30, HSZ/403
Dielectric and light scattering dynamic susceptibility of molecular liquids on approaching Tg — •Alexander Brodin1, Sergei Adichtchev1, Rikard Bergman2, Thomas Blochowicz1, Catalin Gainaru1, Per Jacobsson2, Johan Mattsson2, Christian Tschirwitz1, and Ernst Rössler1 — 1Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany — 2Materialfysik, Chalmers Tekniska Högskola, 41296 Göteborg, Sweden
Dynamic susceptibility spectra of any glass forming liquid are known to comprise two main features, a vibrational band in the THz region and an α -relaxation peak, which moves by many decades in frequency on approaching the glass transition. In addition, there may exist a variety of secondary relaxation processes in the frequency range between the two main peaks. We argue that one of these secondary features, namely the so-called excess wing, is indeed a genuine characteristic of the main α -relaxation itself in the sense that it invariably emerges on cooling a liquid through a characteristic temperature a few tens of degrees above the glass temperature. In contrast, the so-called Johari-Goldstein relaxation, showing up as a separate peak with temperature activated frequency behavior, may or may not be present and is therefore a system-dependent quality. We experimentally show that all the mentioned spectral features, albeit with different relative amplitude, are present in both light scattering (PCS and Raman-Brillouin) and dielectric spectra, and are therefore characteristics of the dynamics and not of a particular experimental technique.