The flow and evolution of ice-sucrose crystal mushes

TL;DR

This study investigates the rheological behavior of ice-sucrose suspensions, revealing how viscosity relaxes and shear-thins over time, with crystal ripening influenced by flow-induced breakup and aggregation.

Contribution

It provides a detailed analysis of the rheology and crystal evolution in ice-sucrose suspensions, linking experimental results to mechanistic models of sintering and brittle fracture.

Findings

Viscosity relaxes exponentially after shear rate changes.

Shear thinning follows a power-law with exponent -1.76.

Crystal ripening leads to a slow increase in mean crystal size over time.

Abstract

We study the rheology of suspensions of ice crystals at moderate to high volume fractions in a sucrose solution in which they are partially soluble; a model system for a wide class of crystal mushes or slurries. Under step changes in shear rate, the viscosity changes to a new `relaxed' value over several minutes, in a manner well fitted by a single exponential. The behavior of the relaxed viscosity is power-law shear thinning with shear rate, with an exponent of $-1.76 \pm 0.25$, so that shear stress falls with increasing shear rate. On longer timescales, the crystals ripen (leading to a falling viscosity) so that the mean radius increases with time to the power $0.14 \pm 0.07$. We speculate that this unusually small exponent is due to the interaction of classical ripening dynamics with abrasion or breakup under flow. We compare the rheological behavior to mechanistic models based on flow-induced aggregation and breakup of crystal clusters, finding that the exponents can be predicted from liquid phase sintering and breakup by brittle fracture.