Shear thickening in molecular liquids characterized by inverse melting

TL;DR

This study investigates shear thickening in a molecular solution with inverse melting, revealing a shear rate-dependent transition linked to hydrogen bonding, suggesting a common mechanism behind non-Newtonian behavior and inverse melting.

Contribution

It provides the first detailed rheological analysis of inverse melting liquids, connecting shear thickening to hydrogen bond dynamics and proposing a unified mechanism.

Findings

Shear thickening occurs at a critical shear rate following Arrhenius behavior.

The critical shear rate is related to hydrogen bond energy.

A possible link between non-Newtonian rheology and inverse melting is proposed.

Abstract

We studied the rheological behavior of a molecular solution composed of $\alpha$-cyclodextrin, water and 4-methylpyridine, a liquid known to undergo inverse melting, at different temperatures and concentrations. The system shows a marked non-Newtonian behavior, exhibiting the typical signature of shear thickening. Specifically, a transition is observed from a Newtonian to a shear thickening regime at a critical shear rate $\dot{\gamma}_c$. The value of this critical shear rate as a function of T follows an Arrhenius behavior $\dot{\gamma}_c(T)=$ B exp$(E_a/K_BT)$, with an activation energy $E_a$ close to the value of the hydrogen bond energy of the O-H group of the $\alpha$-CD molecules. We argue that the increase of viscosity vs shear rate (shear thickening transition) is due to the formation of hydrogen bonded aggregates induced by the applied shear field. Finally, we speculate on the possible interplay between the non-Newtonian rheology and the inverse melting behavior, proposing a single mechanism to be at the origin of both phenomena.