Fractional Debye-Stokes-Einstein behaviour in an ultraviscous nanocolloid: glycerol and silver nanoparticles

TL;DR

This study investigates the fractional Debye-Stokes-Einstein behaviour in glycerol and its nanocolloid with silver nanoparticles under high pressure, revealing a transition to strongly decoupled dynamics in the nanocolloid at 1.2 GPa.

Contribution

It demonstrates pressure-induced decoupling in nanocolloids, linking FDSE exponent changes to fragility and activation parameters, advancing understanding of ultraviscous liquid dynamics.

Findings

Decoupling becomes significant at 1.2 GPa in nanocolloid

Pure glycerol shows milder decoupling under pressure

FDSE exponent relates to fragility and activation enthalpy

Abstract

One of hallmark features of glass forming ultraviscous liquids is the decoupling between translational and orientational dynamics. This report presents studies of this phenomenon in glycerol, a canonical molecular glass former, heading for the impact of two exogenic factors: high pressures up to extreme 1.5 GPa and silver (Ag) nanoparticles (NP). The analysis is focused on the fractional Debye-Stokes-Einstein (FDSE) relation $\sigma(T,P)*(\tau(T,P))^S = const$, linking DC electric conductivity $(\sigma)$ and primary $(\alpha)$ relaxation time $(\tau_\alpha)$. In glycerol and its nanocolloid (glycerol with Ag-NP) under atmospheric pressure only the negligible decoupling $(S = 1)$ was detected. However, in the compressed nanocolloid a well-defined transformation (at P = 1.2 GPa) from $S \thickapprox 1$ to the very strongly decoupled dynamics $(S \thickapprox 0.5)$ occurred. For comparison, in pressurized 'pure' glycerol the stretched shift from $S \thickapprox 1$ to $S \thickapprox 0.7$ took place. This report presents also the general discussion of FDSE behavior in ultraviscous liquids, including the new link between FDSE exponent, fragility and the apparent activation enthalpy and volume.