Light scattering study on the glass former o-terphenyl

Area of Science:

• Condensed Matter Physics
• Materials Science
• Physical Chemistry

Background:

• Understanding the dynamic susceptibility of glass formers is crucial for explaining their unique properties.
• Previous studies have explored various dynamic processes but often with limited time or temperature ranges.
• The interplay between fast and slow dynamics in glass formers remains an active area of research.

Purpose of the Study:

• To comprehensively investigate the dynamic susceptibility of the glass former o-terphenyl over an extended temperature range (240-440 K).
• To bridge the gap between photon correlation spectroscopy (PCS) and tandem Fabry-Pérot interferometry (TFPI) for a wider time domain coverage.
• To identify and characterize dynamic crossover phenomena in o-terphenyl.

Main Methods:

• Combined use of double monochromator, tandem Fabry-Pérot interferometry (TFPI), and photon correlation spectroscopy (PCS).
• Achieved a time resolution of 6 ns with the PCS setup, significantly reducing the measurement gap between PCS and TFPI.
• Acquired combined time-domain data spanning from 0.01 ps to 100 s.

Main Results:

• The primary alpha-process in o-terphenyl exhibits frequency-temperature superposition across the entire investigated temperature range, with no change in shape or amplitude.
• An excess wing contribution emerges, causing a flattening of the susceptibility minimum near the glass transition temperature (T(g)).
• A distinct cusplike temperature dependence was determined for the relaxation strength of fast dynamics, with a crossover temperature T(c) = 316 ± 10 K.

Conclusions:

• The study confirms the robustness of frequency-temperature superposition for the primary alpha-process in o-terphenyl.
• The identified crossover temperature for fast dynamics is higher than previously reported due to the absence of extrapolation schemes.
• The findings provide a more complete picture of the dynamic susceptibility and relaxation mechanisms in glass formers.