On the nature of the supercooled liquid state of quadrol.

Abstract

The dynamic behaviour of quadrol (N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine) in its glassy and supercooled liquid states is examined through a combined experimental and computational approach. Owing to its strong hydrogen-bonding capability and stereochemical complexity, quadrol avoids crystallization and exhibits a glass transition close to -30 °C. Dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC) have been employed to probe the α-relaxation, secondary relaxation modes and physical aging phenomena. The α-relaxation shows a marked non-Arrhenius temperature dependence and dominates the dielectric response, either in DRS and TSDC results; additionally, calorimetric and TSDC measurements reveal a strong sensitivity to thermal history and aging conditions. Below Tg, two secondary relaxations become clearly discernible. The faster γ-relaxation, which appears at lowest temperatures, exhibits kinetic features characteristic of localized molecular motions. By contrast, the slower β-relaxation shows a pronounced sensitivity to both aging and water content, signaling a more complex underlying mechanism. The dc electrical conductivity follows a VFTH-like temperature dependence and displays a partially decoupled from the α relaxation. Complementary molecular simulations provide atomistic insight into conformational preferences and hydrogen-bonding environments, offering a microscopic basis for the observed relaxation behaviour. Taken together, these results reinforce the value of quadrol as a model system for probing the interplay between molecular mobility, hydrogen bonding, and dynamic arrest in amorphous organic materials.