Physical ageing studied by a device allowing for rapid thermal equilibration

TL;DR

This study introduces a novel device with rapid thermal equilibration capabilities to investigate the ageing process of organic glasses, revealing a consistent internal clock and simple exponential relaxation at long times.

Contribution

The paper presents a new microregulator device that extends observable ageing times by nearly two orders of magnitude, enabling detailed analysis of structural ageing in organic glasses.

Findings

Existence of an 'inner clock' controlling structural ageing.

Relaxation at long times is simple exponential, not stretched.

No 'expansion gap' observed between relaxation rates after temperature jumps.

Abstract

Ageing of organic glasses to the equilibrium liquid state is studied by measuring the dielectric loss utilizing a microregulator where temperature is controlled by means of a Peltier element. Compared to conventional equipment the new device adds almost two orders of magnitude to the span of observable ageing times. Data for five organic glass-forming liquids are presented. The existence of an "inner clock" is confirmed by a model-free test showing that the ageing of structure is controlled by the same material time that controls the dielectric properties. At long times relaxation is not stretched, but simple exponential, and there is no "expansion gap" between the limits of the relaxation rates following up and down jumps to the same temperature.