Anomalous decoupling dynamics in glycerol and its nanocolloid with silver nanoparticles

TL;DR

This study investigates the decoupling of rotational and translational dynamics in glycerol and its silver nanoparticle nanocolloid under high pressure, revealing strong decoupling effects and questioning the universality of fractional exponents.

Contribution

It provides new insights into decoupling behavior in ultraviscous glycerol and nanocolloids, especially under high pressure, challenging existing universality assumptions.

Findings

Decoupling exponent S varies with pressure and temperature.

Strong decoupling observed at high pressure in nanocolloid, with S approaching 0.5.

Crossover from coupled to decoupled dynamics occurs at GPa pressures.

Abstract

Orientational and translational decouplings in ultraviscous glass forming glycerol and its nanocolloid based on Ag nanoparticles, as the function of temperature and pressure up to challenging P more than 1.5 GPa, are discussed. The analysis is focused on the fractional Debye-Stokes-Einstein relation FDSE sigma times tau to the power S equals const., where tau and sigma are for the structural relaxation time and electric conductivity are functions of T and P, respectively. For temperature tests in glycerol the clear evidence for the almost coupled exponent S equals 1 was obtained. For the supercooled nanocolloid the crossover to the decoupled domain associated with S equals 0.91 was noted. In super pressed glycerol and the nanocolloid the clear cross over from the domain described by the exponent S equals 1 to S less than 1 appeared on the GPa domain. For the nanocolloid it is associated with particularly strong decoupling, related to S equals 0.5, and occurs at well-defined pressure. This can suggest a possible fluid-fluid transition. Questions related to the validity of the Debye-Stokes tau equals approx. eta over T and Maxwell tau equals approx. eta relations, where eta is for viscosity, are also addressed. Results obtained do not support the recently suggested universality of the fractional exponent describing orientational and translational decoupling.