Extreme breakdown of the Einstein relation in liquid water under centrifugation

TL;DR

This study reveals that the Einstein relation fails in water under strong centrifugation, with solute migration significantly slower than predicted, and introduces a new scaling law related to solute density and centrifugation.

Contribution

It uncovers the complete breakdown of the Einstein relation in water under centrifugation and proposes a two-phase model to describe solute behavior and a new scaling law.

Findings

ER breaks down in pure water under centrifugation

Solutes migrate at 5% of predicted speed

A new scaling law relates solute density, acceleration, and transition concentration

Abstract

We present evidence that the Einstein relation (ER) breaks down completely in pure water and dilute aqueous solutions under strong centrifugation fields at 40 oC. Isotopologues (e.g., H2O-18) and solutes migrate at a speed of only 5% of that predicted based on the ER. The ER is restored with the addition of solutes above a transition concentration (ct). We further discovered a new scaling law between the solute's partial molar density, the centrifugal acceleration, and ct, which can be quantitatively described by a two-phase model in analog to the Avrami model for phase transformation. The breakdown may stem from long-range dipole interactions or the hydrogen bond network in water, which are disrupted by the presence of solutes. This report shows that studying transport under centrifugation can be a new strategy to understand fundamental transport properties and complex interactions in liquids.