Yield Stress Fluids Solidifying in Capillary Imbibition

TL;DR

This paper investigates the liquid-to-solid transition of yield stress fluids during capillary imbibition, revealing unexpected flowing behavior below the yield stress and proposing a rheological model to explain it.

Contribution

It introduces a new model capturing the solidification process of yield stress fluids during capillary imbibition, highlighting a universal flowing behavior below the yield stress.

Findings

Yield stress fluids can flow below their yield stress during capillary imbibition.

A rheological model with slip explains the observed behavior.

The behavior is universal across different YSFs.

Abstract

When subjected to an external stress that exceeds the yield stress ($\sigma_\mathrm{Y}$), yield stress fluids (YSFs) undergo a solid-to-liquid transition. Despite the extensive studies, there has been limited attention to the process of liquid-to-solid transition. This work examines the solidification of YSFs through capillary imbibition, easily observed in the processes of wetting, coating, spreading, and wicking. During gradual deceleration of the capillary rise, YSFs display an unexpected flowing behavior, even when subjected to stresses below the $\sigma_\mathrm{Y}$. We propose a model with numerical solutions based on rheological properties of YSFs and slip to capture this unusual, yet universal behavior.