Mode-coupling Crossover Research Articles

Mode-coupling crossover in viscous toluene revealed by neutron and light scattering

The dynamics of supercooled toluene, studied in a GHz-THz range by incoherent neutron and depolarized light scattering, is found to be in full accord with mode coupling predictions. Around the susceptibility minimum, neutron spectra are wavenumber independent and proportional to light scattering data; the fast β-relaxation scaling law applies; amplitude and frequency diverge with power laws that extrapolate towards a crossover temperature Tc K.

Coherent dynamic structure factor of orthoterphenyl around the mode coupling crossover temperatureTc

The coherent dynamic structure factor of supercooled orthoterphenyl has been measured by time-of-flight neutron scattering. The data extend previous backscattering and spin-echo data towards shorter times. In the $\ensuremath{\beta}$ relaxation regime the two-step decay of density correlations can be described by the same master function as found before for self-correlations. We show that the mode-coupling crossover temperature ${T}_{c}$ can be determined from $\ensuremath{\beta}$ relaxation data alone. The wave-number dependence of the relaxation amplitude follows, to some extent, that of the static structure factor.

Brillouin scattering in salol: DeterminingTcof the mode coupling theory

Brillouin scattering spectra of the molecular glass former salol were combined with ultrasonic measurements to evaluate the nonergodicity parameter of mode coupling theory ${\mathit{f}}_{0}$(T). It was found to exhibit a weak cusp at a temperature ${\mathit{T}}_{\mathit{c}}^{\mathit{B}}$=275\ifmmode\pm\else\textpm\fi{}10 K in reasonable agreement with the mode-coupling crossover temperature ${\mathit{T}}_{\mathit{c}}$=256\ifmmode\pm\else\textpm\fi{}5 K found recently by other methods. This result is in marked contrast to the recent publication of Elmroth, Borjesson, and Torell [Phys. Rev. Lett. 68, 79 (1992)].